Nitrogen Balance for Pulse Crops in Rotation with Spring Wheat
US Department of Agriculture, Agricultural Research Service, Northern Plains Agricultural Research Laboratory, 1500 North Central Avenue, Sidney, MT 59270, USA
Agronomy 2026, 16(4), 463; https://doi.org/10.3390/agronomy16040463
Submission received: 29 January 2026
/
Revised: 12 February 2026
/
Accepted: 13 February 2026
/
Published: 16 February 2026
(This article belongs to the Special Issue Nitrogen Cycling and Efficient Utilization Mechanisms in Agricultural Field Ecosystems)
Abstract
Pulse crops, having the capacity for biological nitrogen (N) fixation, rarely receive N fertilizers, but information is scarce on N balance for pulse crops or pulse crop-spring wheat (Triticum aestivum L.) rotations. The objective of the study was to evaluate N balance based on N inputs and outputs and soil N sequestration rate for pulse crops and pulse crop-spring wheat rotations from 2021 to 2024 in the US northern Great Plains. Pulse crops (chickpea [Cicer arietinum L.], lentil [Lens culinaris Medik.], and pea [Pisum sativum L.]) were rotated with spring wheat to form four crop rotations (chickpea–spring wheat, lentil-spring wheat, pea–spring wheat, and spring wheat–spring wheat). Total N input from N fertilization, biological N fixation, soil N mineralization, crop seed, and precipitation was 9–27% greater for pea than for other crops and greater for pea–spring wheat than chickpea–spring wheat and continuous spring wheat. Total N output from grain N removal, ammonia volatilization, denitrification, plant senescence, leaching, surface runoff, and gaseous emissions was 20–62% greater for spring wheat than pulse crops. Nitrogen sequestration rate at 0–15 cm was 89% greater for spring wheat than lentil and 106–107% greater for pea-spring wheat and spring wheat–spring wheat than lentil–spring wheat. Nitrogen balance was 215–356% greater for chickpea and pea than lentil and spring wheat and 114–118% greater for chickpea–spring wheat and pea–spring wheat than lentil–spring wheat. Greater N input increased N surplus for pea or pea-spring wheat, and greater N output increased N deficit for spring wheat or spring-spring wheat compared to lentil or lentil–spring wheat, indicating that pea alone or in rotation with spring wheat reduced N loss to the environment by increasing soil N storage compared to continuous spring wheat.
1. Introduction
Nitrogen fertilization is needed to enhance crop yields and quality to feed the growing population and nourish lives, but it can also pollute the environment, which results in significant risks to human and animal health and ecosystems [1,2], causing more than $157 billion damage [3]. This is because crops can take up only 40 to 60% of applied N [4,5,6], resulting in the significant accumulation of soil residual N (NO3-N + NH4-N), which can be lost to the environment through leaching, denitrification, volatilization, surface runoff, soil erosion, and gaseous emissions [7,8,9,10]. Such losses can range from 20 to 55% of the total N input [11,12,13,14]. Soil acidification from the accumulation of soil residual N can also degrade soil fertility and health [15,16]. Accumulation of soil residual N and N loss to the environment can be reduced either by decreasing N fertilization rate or by increasing N-use efficiency [8,10,17,18]. Because of the biological N fixation, pulse crops alone or in rotations with nonlegumes can reduce the accumulation of soil residual N and N loss to the environment because pulse crops receive little or no N fertilizer [19,20,21].
Nitrogen balance is the difference between total N input, total N output, and annual soil N sequestration rate [10,21,22]. Total N input involves inputs from N fertilization, irrigation water, dry and wet (snow and rain) depositions from the atmosphere, biological N fixation, soil N mineralization, non-symbiotic N fixation, and crop seeds [8,10,17]. Total N output involves outputs from crop grain and/or biomass harvest and N losses to the environment through leaching, denitrification, volatilization, surface runoff, soil erosion, and gaseous emissions [7,8,9,10]. The unharvested portion of N in plant components, such as N in crop residue and roots, can convert either into labile fractions (NH4-N and NO3-N) that become available to plants or to nonlabile fractions, such as organic N, which is stored in the soil. Additionally, N is also mineralized from soil organic matter that becomes available to plants. Nitrogen sequestration rate refers to the annual change in soil total N between final and initial soil N levels. Nitrogen balance shows dominant processes of N flows in the agroecosystems, measures agronomic performance and environmental sustainability [10,22], and is a robust measure of N loss to the environment [23]. Neutral N balance can be achieved by matching N inputs and outputs in space and time while maintaining or increasing crop yields [24].
As application of N fertilizers to crops and mineralization of soil organic matter and crop residue result in the accumulation of soil residual N, N fertilization rates are usually adjusted for crops by deducting soil residual N from desired N rates to reduce the negative consequences on soil health and environmental quality [8,10,18]. Because it takes a long time to determine N mineralization from soil organic matter during the crop growing season, it is estimated that about 1% of soil organic N to a depth of 30 cm is mineralized every year, depending on soil temperature and water content, residue addition (fresh or old residue), and soil organic matter [5,6]. Because of the difficulty and complexity of measuring values for some N inputs and outputs, these values are usually estimated from the literature, which adds uncertainty to the calculation of N balance [4,10,17,21].
Cropping systems can variably affect N balance. Kehoe et al. [25] found that N balance was negative for pea, which did not receive N fertilizer due to biological N fixation. Groffman et al. [26] reported that N balance was positive for the fertilized cropping system but negative for the unfertilized system. In contrast, some researchers [10,20,27] demonstrated that legume-based cropping systems have neutral or positive N balance due to legume N fixation and reduced N fertilization rate to succeeding nonlegume crops in the rotation compared with nonlegume monocropping, which has negative N balance. Sainju et al. [21] observed that N balance was near neutral for barley (Hordeum vulgare L.)–pea rotation due to greater N input and reduced N loss compared to negative N balance for continuous barley, which showed greater N loss and lower N input.
Studies on N balance for pulse crops and pulse crop–nonlegume rotations need further exploration due to the complex nature of biological N fixation, N losses to the environment, and adjustment of N fertilization rates to succeeding nonlegume crops in the rotation. This study examined N balance for pulse crops and spring wheat following spring wheat in the crop rotation and pulse crop–spring wheat rotations by taking into account of total N input and output and N retention in the soil from 2021 to 2024 in the US northern Great Plains. The research questions were: (1) Do pulse crops have N surplus compared to spring wheat? (2) Do pulse crop–spring wheat rotations have neutral or positive N balance compared to continuous spring wheat? It was hypothesized that (1) pulse crops would have positive N balance compared to spring wheat due to greater total N input compared to total output and (2) that pulse crop–spring wheat rotations would have neutral or positive N balance due to reduced N fertilization rate to spring wheat and N loss to the environment compared to continuous spring wheat. The objective of the study was to examine total N inputs and outputs, N sequestration rate, and N balance for pulse crops and spring wheat following spring wheat in the rotation, and pulse crop–spring wheat rotations from 2021 to 2024 in dryland cropping systems in the US northern Great Plains.
2. Materials and Methods
2.1. Experimental Details
The experiment was performed from 2021 to 2024 in Sidney (48° 33′ N, 104° 50′ W), Montana, USA. The experimental site has a mean (30 yr average) annual air temperature of 7 °C and an annual precipitation of 341 mm. The site had soil classified as Williams loam (fine-loamy, mixed, superactive, frigid, Typic Argiustolls), with 350 g kg−1 sand, 325 g kg−1 silt, 325 g kg−1 clay, 13.2 g kg−1 organic matter, and 7.2 pH at the 0 to 20 cm depth. The site was under conventional tillage with continuous spring wheat for 10 yr before the initiation of the experiment.
Three pulse crops (chickpea, lentil, and pea), along with a control (spring wheat), were grown in rotation with spring wheat to establish four crop rotations: chickpea–spring wheat, lentil–spring wheat, pea–spring wheat, and spring wheat–spring wheat. Each crop rotation had both phases of crops occurring in each year. All crops and crop rotations were arranged in a randomized block design with four replications. The plot size was 15 × 6 m.
Using a no-till drill, all crops were planted to a depth of 3.8 cm under the no-till condition from late April to early May 2021–2024. Seeding rate for chickpea (cv. Orion) was 200 kg ha−1, lentil (cv. Maxum red) was 70 kg ha−1, pea (cv. Majoret) was 180 kg ha−1, and spring wheat (cv. Vida) was 80 kg ha−1, with each row spaced 20 cm. Chickpea seeds were inoculated with Rhizobium ciceri, and lentil and pea seeds were inoculated with Rhizobium leguminosarum before planting. At seeding, P fertilizer as monoammonium phosphate at 11 kg P ha−1 and K fertilizer as muriate of potash at 27 kg K ha−1 were banded to all crops, 5 cm to the side and 5 cm below seeds every year. At the same time, pulse crops received N fertilizer from monoammonium phosphate at 5 kg N ha−1, and spring wheat received a banded application of N fertilizers from urea and monoammonium phosphate at 100 kg N ha−1. Because of the presence of soil residual NO3-N due to N supplied from N fertilizers and mineralization of crop residue and soil organic matter, N fertilization rate for spring wheat was adjusted to soil NO3-N content to a depth of 60 cm determined in the autumn of the previous year. Therefore, desired N fertilization rate for spring wheat included both soil and fertilizer N. The actual amount of N fertilizer applied for spring wheat varied from 52 kg N ha−1 in 2022 to 73 kg N ha−1 in 2021 (Table 1). Crops were grown under rainfed conditions without irrigation. All crops received recommended doses of herbicides and pesticides before, during, and after crop growth [28].
Two days before grain harvest from late July to mid-August each year, plant samples were collected from four 1 m rows randomly outside yield rows in each plot. These were separated into straw and grain, and straw yield was determined by oven-drying straw at 70 °C for 3 d. Grain yield was determined by harvesting grains with a plot combine from an area of 11.0 × 1.5 m after oven-drying a subsample at 70 °C for 7 d. After grain harvest, crop residue was returned to the soil. A sample of oven-dried straw and grain was ground to 1 mm, and N concentrations in straw and grain were determined by the dry combustion method using a C and N analyzer (LECO, St. Joseph, MI, USA). Nitrogen content in straw and grain N removal was calculated by multiplying straw and grain yields by their N concentrations.
2.2. Soil Sampling for the Measurement of Root Biomass and Total Nitrogen
After crop harvest in August 2021–2024, soil samples for the measurement of root biomass N were collected from the 0–120 cm depth from four locations randomly within a plot using a hydraulic probe (5 cm inside diameter) mounted in a truck. The soil cores were divided into five depth intervals (0–15, 15–30, 30–60, 60–90, and 90–120 cm), placed in plastic bags, and stored at 4 °C until root separation from the soil. About 10 g of root-free soil samples at 0–15 cm was separated from each soil core to determine soil N mineralization, as shown below. The rest of the soil samples from the cores were placed in 0.5 mm sieves in a hydropneumatic elutriator and washed with water for 2 hr until all silt and clay particles were removed [29]. The remaining roots and sand particles were transferred to a 500 mL beaker containing 300 mL distilled water. Floated coarse and fine roots in the water were picked with tweezers. Roots from four locations within a plot were composited by depth, and root biomass was determined after oven-drying roots at 70 °C for 3 d. Nitrogen concentration in root biomass was determined using a C and N analyzer as above, after grinding roots to 1 mm. Nitrogen content in root biomass at a depth was determined by multiplying root biomass by N concentration. Root biomass N at 0–120 cm was determined by adding biomass N from individual depth layers.
The root-free soil samples at 0–15 cm from four plots were composited, from which 10 g soil was oven -dried at 110 °C for 24 hr to determine soil bulk density by dividing the weight of the oven dried soil by the volume of the core. The rest of the samples were air- dried and ground to 2 mm. Nitrogen concentration in the soil was determined using a C and N analyzer as above, after further grinding a portion of the subsample to 0.5 mm. Soil total N was calculated by multiplying N concentration by the bulk density and the thickness of the soil layer. Soil N mineralization was calculated by multiplying soil total N by 0.01 (1% of soil total N) [5]. It was considered that soil N mineralization calculated for samples after crop harvest in August each year would represent N mineralization for the whole year.
Because of the variations in the date of soil sampling, soil total N determined in the above soil samples could not be used to determine soil N sequestration rate. As a result, a separate set of soil samples was collected at 0–15 cm from five locations randomly within a plot using the hand probe (2.5 cm inside diameter) in April 2021 and October 2024 to determine soil N sequestration rate. A subsample (10 g) from each soil core was oven -dried at 110 °C for 24 hr, from which soil bulk density was calculated by dividing the weight of the oven-dried soil by the volume of the core. The remaining samples were composited, air- dried, and ground to 2 mm. Nitrogen concentration in these samples was determined using a C and N analyzer as above. Soil total N was calculated by multiplying N concentration by the bulk density and the thickness of the soil layer. Nitrogen sequestration rate was calculated by dividing the difference in soil total N between October 2024 and April 2021 by the number of years (4.5).
2.3. Nitrogen Balance
Total N input was calculated as:
where Na = N fertilizer amount, Nb = biological N fixation, Nc = soil N mineralization, Nd = atmospheric N deposition, Ne = crop seed N, and Nf = non-symbiotic N fixation. Biological N fixed by pulse crops (Nb) was calculated as:
where 0.7 is the conversion factor, assuming that 70% of N is fixed by pulse crops and 30% is taken up from the soil [4,10,17]. The biological N fixation for spring wheat was considered zero. The soil N mineralization (Nc) was estimated as 1% of soil total N [5,6] at 0–15 cm. The atmospheric N deposition (Nd) included both wet (rain and snow) and dry (absorption of ammonia and other compounds by the soil from the atmosphere) depositions and was estimated as 7 kg N ha−1 yr−1 for all crops, crop rotations, and years [4,10,30]. The crop seed N (Ne) was calculated by multiplying the seeding rate by N concentration. The non-symbiotic N fixation (Nf) by blue-green algae and free-living soil bacteria was estimated as 5 kg N ha−1 for all crops, crop rotations, and years [10,30,31].
Total N input = Na + Nb + Nc + Nd + Ne + Nf
Nb = 0.7 × (straw N + grain N + root biomass N [0 − 120 cm])
Total N output was calculated as:
where Ng = crop grain N removal, Nh = ammonia volatilization, Ni = denitrification loss, Nj = plant senescence loss, Nk = leaching loss, Nl = gaseous (NO, N2O, and NO2) emissions, and Nm = surface runoff loss. Ammonia volatilization (Nh) was estimated as 15% of applied N fertilizer [4,32]. Nitrogen loss from denitrification (Ni) was estimated as 13% of total N applied from N fertilizer and atmospheric N deposition after deducting ammonia volatilization, considering that denitrification loss of biologically fixed N was negligible [4,31]. Nitrogen loss from plant senescence (Nj) was calculated as 5% of aboveground biomass N (straw N + grain N) [4,30]. Nitrogen leaching loss (Nk) for the semiarid region was estimated as 10 kg N ha−1 yr−1 for spring wheat and 12 kg N ha−1 yr−1 for pulse crops [10,33]. Nitrogen losses from gas emissions (Nl) and surface runoff (Nm) were estimated as 1.5% and 1.0% of applied N fertilizer, respectively [10,34,35].
Total N output = Ng + Nh + Ni + Nj + Nk + Nl + Nm
Nitrogen balance [29] was calculated as:
Nitrogen balance = Total N input − total N output ± N sequestration rate
Nitrogen sequestration rate was considered positive when N was gained in the soil from April 2021 to October 2024 and negative when N was lost. A positive N balance indicated N surplus and a negative N balance indicated N deficit in the agroecosystem. The N balance was used to evaluate the performance of the agroecosystem and environmental sustainability due to N inputs, outputs, and retention in the soil. Because some N input and output values were estimated from the literature for the calculation of N balance, the uncertainty in N balance was shown as the standard deviation of the mean values.
The N loss to the environment/total N input ratio (Nle) was calculated as:
Nle (%) = (Total N output − Ng) × 100/total N input
2.4. Statistical Data Analysis
Data for N inputs, N outputs, soil total N, N sequestration rate, and N balance for a crop rotation were calculated by averaging values for crop phases within the rotation in a year. Data for crop (pulse crop or spring wheat following spring wheat in the rotation) or crop rotation were analyzed using the MIXED procedure of SAS (SAS/STAT 15.2) after checking for homogeneity of variance and normal distribution [36]. Crop or crop rotation was considered as the fixed effect, replication as the random effect, and year as the repeated measure variable for data analysis. Means and interactions were separated byusing the least square means test when significant [36]. Differences were considered statistically significant at p ≤ 0.05, unless otherwise stated.
3. Results
3.1. Nitrogen Inputs
3.1.1. Nitrogen Fertilizer Amount
The N fertilizer amount was significantly affected by crop, year, and crop × year interaction (Table 1). Nitrogen fertilizer amount was similar for pulse crops in all years, because monoammonium phosphate supplied N at 5 kg N ha−1 while applying as a P fertilizer to all crops. However, N fertilizer amount was greater for spring wheat than pulse crops in all years. Nitrogen fertilizer amount was greater in 2021 and lower in 2022 than in other years.
Nitrogen fertilizer amount was also significantly affected by crop rotation and crop rotation × year interaction (Table 1). In 2021, N fertilizer amount was 87% greater for spring wheat–spring wheat than pulse crop–spring wheat rotations. In 2023, N fertilizer amount was 85–118% greater for spring wheat–spring wheat than pulse crop–spring wheat rotations. There was no significant difference in N fertilizer amount among crop rotations in 2022 and 2024. Averaged across years, N fertilizer amount was 76–91% greater for spring wheat–spring wheat than pulse crop-spring wheat rotations.
3.1.2. Biological Nitrogen Fixation
Biological N fixation was significantly affected by crop, year, and crop × year interaction (Table 1). Biological N fixation was 25–30% greater for chickpea and pea than lentil in 2022. In 2023, biological N fixation was 19% greater for lentil than pea. In 2024, biological N fixation was 189–208% greater for lentil and pea than chickpea. Averaged across years, biological N fixation was 9–37% greater for pea than chickpea and lentil. Absence of N fixation resulted in zero biological N fixation for spring wheat. Averaged across crops, biological N fixation was greater in 2024 than in other years.
Biological N fixation was also significantly affected by crop rotation and crop rotation × year interaction (Table 1). In 2022, biological N fixation was 25–31% greater for chickpea–spring wheat and pea–spring wheat than lentil–spring wheat. In 2023, biological N fixation was 19% greater for lentil–spring wheat than chickpea–spring wheat. In 2024, biological N fixation was 189–208% greater for lentil–spring wheat and pea–spring wheat than chickpea–spring wheat. Averaged across years, biological N fixation was 26–37% greater for lentil–spring wheat and pea–spring wheat than chickpea–spring wheat.
3.1.3. Soil Nitrogen Mineralization
Soil N mineralization was significantly affected by year, but crop, crop rotation, crop × year, and crop rotation × year interactions were not significant (Table 2). Soil N mineralization ranged from 24.2 kg N ha−1 for lentil in 2022 to 34.6 kg N ha−1 for spring wheat in 2024. Similarly, soil N mineralization ranged from 24.3 kg N ha−1 for lentil–spring wheat in 2023 to 33.9 kg N ha−1 for spring wheat–spring wheat in 2021. Averaged across crops and crop rotations, soil N mineralization was greater in 2021 and 2023 than in 2022 and 2024.
3.1.4. Crop Seed Nitrogen
Crop seed N was significantly affected by crop, crop rotation, crop × year, and crop rotation × year interactions (Table 2). In all years, crop seed N was 152–236% greater for chickpea and pea than lentil and spring wheat. Similarly, crop seed N was 80–118% greater for chickpea–spring wheat and pea–spring wheat than lentil–spring wheat and spring wheat–spring wheat.
3.1.5. Total Nitrogen Input
Total N input was significantly affected by crop, crop rotation, year, crop × year, and crop rotation × year interactions (Table 3). Total N input was 11% greater for pea than lentil in 2021. In 2022, total N input was 21–47% greater for chickpea and pea than lentil and spring wheat. In 2023, total N input was 17–18% greater for lentil and pea than spring wheat. In 2024, total N input was 30–85% greater for pea than chickpea, lentil, and spring wheat. Averaged across years, total N input was 10–27% greater for pea than other crops.
Total N input was 8–9% greater for pea–spring wheat and spring wheat–spring wheat than lentil–spring wheat in 2021 (Table 3). In 2022, total N input was 25–26% greater for chickpea–spring wheat and pea–spring wheat than spring wheat–spring wheat. In 2024, total N input was 22–37% greater for lentil–spring wheat and pea–spring wheat than chickpea–spring wheat and spring wheat–spring wheat. Averaged across years, total N input was 9–13% greater for pea–spring wheat than chickpea–spring wheat and spring wheat–spring wheat. Averaged across crops and crop rotations, total N input was lower in 2022 than in other years.
3.2. Nitrogen Outputs
3.2.1. Crop Grain Nitrogen Removal
Crop grain N removal was significantly affected by crop, crop rotation, year, crop × year, and crop rotation × year interactions (Table 4). Crop N removal was 40% greater for spring wheat than lentil in 2022. In 2023, crop N removal was 33–58% greater for spring wheat than pulse crops. In 2024, crop N removal was 310–351% greater for lentil, pea, and spring wheat than chickpea. Mean crop N removal across years was 15–53% greater for spring wheat than chickpea and lentil.
In crop rotations, crop N removal was 51–77% greater for lentil–spring wheat, pea–spring wheat, and spring wheat–spring wheat than chickpea–spring wheat in 2024. There was no significant difference in crop N removal among crop rotations from 2021 to 2023. Averaged across years, crop N removal was 17–21% greater for lentil–spring wheat and pea–spring wheat than chickpea–spring wheat. Averaged across crops and crop rotations, crop N removal was lower in 2021 than in other years.
3.2.2. Nitrogen Losses to the Environment
Nitrogen losses from ammonia volatilization, denitrification, leaching, gaseous emissions, and surface runoff were greater for spring wheat than pulse crops or greater for spring wheat–spring wheat than pulse crop–spring wheat rotations in all years (Table 4, Table 5, Table 6 and Table 7). Nitrogen loss from plant senescence was 40–49% greater for chickpea, pea, and spring wheat than lentil in 2022 (Table 5). In 2023, N loss from plant senescence was 30–55% greater for spring wheat than pulse crops. In 2024, N loss from plant senescence was 271–318% greater for lentil, pea, and spring wheat than chickpea. Averaged across years, N loss from plant senescence was 16–51% greater for pea and spring wheat than chickpea and lentil. For crop rotations, N loss from plant senescence was 44–54% greater for lentil–spring wheat and spring wheat–spring wheat than chickpea–spring wheat in 2023. In 2024, N loss from plant senescence was 84–103% greater for lentil–spring wheat, pea–spring wheat, and spring wheat–spring wheat than chickpea–spring wheat. There was no significant difference in N loss from plant senescence among crop rotations in 2021 and 2022. Mean N loss from plant senescence across years was 16–23% greater for lentil–spring wheat and pea–spring wheat than chickpea–spring wheat. Averaged across crops and crop rotation, N loss from plant senescence was lower in 2021 than in other years.
The N loss to the environment/total N input ratio (Nle) was 13–18% greater for spring wheat than pulse crops in 2021 and 2023 (Table 7). In 2022, Nle was 2% greater for lentil than chickpea and pea and 17–19% greater for spring wheat than pulse crops. In 2024, Nle was 5–6% greater for chickpea than lentil and pea and 16–21% greater for spring wheat than pulse crops. Averaged across crops, Nle was 12% greater for chickpea than lentil and pea and 16–18% greater for spring wheat than pulse crops. Averaged across crops, Nle was lower in 2021 than in other years. For crop rotations, Nle did not vary among crop rotations in any year (Table 7). The Nle varied from 22% for pea–spring wheat in 2021 to 34% for spring wheat–spring wheat in 2022 and 2024. Mean Nle across years was 8–9% greater for spring–spring wheat than pulse crop–spring wheat rotations.
3.2.3. Total Nitrogen Output
Total N output was significantly affected by crop, year, and crop × year interaction (Table 3). In 2021, total N output was 27–28% greater for spring wheat than chickpea and lentil. In 2022, total N output was 31–47% greater for chickpea, pea, and spring wheat than lentil. In 2023, total N output was 52–66% greater for spring wheat than pulse crops. In 2024, total N output was 164–244% greater for lentil, pea, and spring wheat than chickpea. Averaged across years, total N output was 27–34% greater for lentil and pea than chickpea and 20–63% greater for spring wheat than pulse crops.
For crop rotations, total N output was significantly affected by year, but crop rotation and crop rotation × year interaction were not significant (Table 3). Total N output ranged from 82.0 kg N ha−1 for lentil–spring wheat in 2021 to 150.8 kg N ha−1 for pea–spring wheat in 2024. Averaged across crops and crop rotations, total N output was lower in 2021 than in other years.
3.3. Nitrogen Sequestration Rate
Soil total N at 0–15 cm at the initiation of the experiment in April 2020 was similar among crops and crop rotations due to five core samples taken from each plot and then composited into one sample to determine N concentration (Table 8). However, soil total N in October 2024 was significantly affected by crop or crop rotation. In 2024, soil total N was 3% greater for pea than lentil or greater for pea–spring wheat than lentil–spring wheat. Soil total N increased from 2020 to 2024, which resulted in a small soil N gain for pea or pea–spring wheat. In contrast, soil total N decreased during the same period that resulted in N loss for other crops and crop rotations. However, N sequestration rate at 0–15 cm was 89–126% greater for pea and spring wheat than lentil. Similarly, N sequestration rate was 93–107% greater for pea–spring wheat and spring wheat–spring wheat than lentil–spring wheat.
3.4. Nitrogen Balance
Nitrogen balance was significantly affected by crop, year, and crop × year interaction (Table 9). Nitrogen balance was 89–90% greater for pea and spring wheat than chickpea in 2021. In 2022, N balance was 149–194% greater for chickpea than lentil and spring wheat. In 2023, N balance was 246% greater for pea than spring wheat. In 2024, N balance was 126–227% greater for chickpea than other crops. Averaged across years, N balance was 76–78% greater for chickpea and pea than lentil and 127–227% greater for pulse crops than spring wheat. The coefficient of variation for N balance for crops ranged from 3% for chickpea in 2023 to 20% for pea in 2021.
Nitrogen balance was also significantly affected by crop rotation, year, and crop rotation × year interaction (Table 9). In 2021, N balance was 166% greater for pea–spring wheat than lentil–spring wheat. In 2023, N balance was 118% greater for chickpea–spring wheat than lentil–spring wheat. In 2024, N balance was 102–103% greater for chickpea–spring wheat than lentil–spring wheat and spring wheat–spring wheat. Averaged across years, N balance was 114–118% greater for chickpea–spring wheat and pea–spring wheat than lentil–spring wheat. Averaged across crops and crop rotations, N balance was greater in 2021 than in other years. The coefficient of variation for N balance for crop rotations ranged from 7% for pea–spring wheat in 2021 to 32% for chickpea–spring wheat in 2023.
4. Discussion
4.1. Nitrogen Inputs
Because of the capacity to fix N biologically, N fertilizers are not usually applied to pulse crops. However, application of monoammonium phosphate as a P fertilizer supplied a small and similar dose of N fertilizer (5 kg N ha−1) to pulse crops in all years (Table 1). Higher N fertilization rate, however, increased the amount of N fertilizer applied to spring wheat compared to pulse crops. Application of N fertilizer to spring wheat also increased N fertilization rate for pulse crop–spring wheat rotations compared to pulse crops alone, but these were lower than spring wheat–spring wheat rotation due to a greater amount of N fertilizer applied for spring wheat. Lower soil residual NO3-N content resulted in a greater amount of N fertilizer applied for spring wheat in 2022 than in other years.
The greater above- and belowground biomass N resulted in increased biological N fixation for chickpea and pea than lentil in 2022 (Table 1). However, lentil performed better due to favorable weather conditions, resulting in greater biological N fixation for this pulse crop than chickpea in 2023. A devastating disease infestation decreased chickpea yield, thereby decreasing biological N fixation for chickpea more than lentil and pea in 2024. Overall, higher shoot and root N resulted in greater biological N fixation for lentil and pea than chickpea. The increased N fixation for pulse crops also showed greater biological N fixation for chickpea–spring wheat and pea–spring wheat than lentil–spring wheat in 2022, greater N fixation for lentil–spring wheat than pea–spring wheat in 2023, and greater N fixation for lentil–spring wheat and pea-spring wheat than chickpea–spring wheat in 2024. Greater straw and grain N uptake for lentil and pea than chickpea was reported by Sainju [28]. Lower growing season (April–August) precipitation decreased biomass yield and, therefore, reduced biological N fixation in 2021 (154 mm) compared to other years (203–252 mm).
Similar levels of soil total N resulted in the non-significant difference in soil N mineralization among crops and crop rotations in all years (Table 2). However, lower soil total N decreased soil N mineralization in 2022 and 2024 compared to other years. Higher seeding rates increased crop seed N for chickpea and pea compared to lentil in all years, as N concentration in pulse crop seeds was not different. Similarly, higher seeding rate and/or N concentration increased crop seed N for chickpea and pea compared to spring wheat in all years. This resulted in greater crop seed N for chickpea–spring wheat and pea–spring wheat than lentil–spring wheat and spring wheat–spring wheat rotations in all years.
Increased biological N fixation increased total N input for pea compared to lentil in 2021, for chickpea and pea compared to lentil in 2022, and for pea compared to chickpea and lentil in 2024 (Table 3). Greater biological N fixation relative to the amount of N fertilizer applied increased total N input for pulse crops compared to spring wheat from 2022 to 2024, except for chickpea in 2024, as the amount of N fertilizer applied for pulse crops was minor. This also increased the overall total N input for pea compared to lentil and chickpea and increased for pulse crops compared to spring wheat. Similarly, greater biological N fixation and the amount of applied N fertilizer increased total N input for pea–spring wheat and spring wheat–spring wheat compared to lentil-spring wheat in 2021, for chickpea–spring wheat and pea–spring wheat compared to spring wheat–spring wheat in 2022, and for lentil–spring wheat and pea–spring wheat compared to other crop rotations in 2024. Decreased biological N fixation and the amount of N fertilizer applied to spring wheat also reduced total N input in 2022 compared to other years.
4.2. Nitrogen Outputs
Similar levels of grain yield and/or N concentration probably resulted in the non-significant difference in crop N removal among pulse crops in all years, except for chickpea in 2024, when a severe disease infestation reduced grain yield and, therefore, crop N removal (Table 4). Overall, pea and lentil removed more N than chickpea. However, greater crop N removal for spring wheat than lentil in 2022, greater removal than pulse crops in 2023, and greater removal than chickpea in 2024 was likely due to increased crop yield stemming from higher N fertilizer rate, although grain N concentration was lower. Increased grain N removal for spring wheat compared to pulse crops due to higher N fertilization rate was also reported by several researchers [37,38]. Because of greater N removal by spring wheat, crop N removal was not significantly different among pulse crop–spring wheat and spring wheat–spring rotations in all years, except in 2024, when lower N removal by chickpea reduced crop N removal for chickpea–spring wheat compared to other crop rotations. Lower grain yields due to decreased growing season precipitation reduced crop N removal in 2021 compared to other years.
Nitrogen losses to the environment due to ammonia volatilization, denitrification, leaching, surface runoff, and gaseous emissions were similar among pulse crops because N fertilization rate was similar among pulse crops (Table 1, Table 4, Table 5, Table 6 and Table 7). It was not known how much of the biological N fixation from these processes was lost, as measurements of these parameters were beyond the scope of this study, and estimated values were not available in the literature. As a result, these losses were considered minor. However, greater N losses for spring wheat than pulse crops were probably due to higher N fertilization rate. This also resulted in greater N losses for spring wheat–spring wheat than pulse crop–spring wheat rotations. Increased crop N removal resulted in greater N loss due to plant senescence for chickpea, pea, and spring wheat than lentil in 2022, greater for spring wheat than pulse crops in 2023, and greater for lentil, pea, and spring wheat than chickpea in 2024 (Table 5). Similarly, increased crop N removal resulted in greater N loss due to plant senescence for lentil–spring wheat and spring wheat–spring wheat than chickpea–spring wheat in 2023 and greater for lentil–spring wheat, pea–spring wheat, and spring wheat–spring wheat than chickpea–spring wheat in 2024.
The greater crop N removal increased total N output for spring wheat compared to pea and lentil in 2021, for chickpea, pea, and spring wheat compared to lentil in 2022, for spring wheat compared to pulse crops in 2023, and for lentil, pea, and spring wheat compared to chickpea in 2024 (Table 3), as N outputs from other processes were smaller. Overall, chickpea had the lowest, but spring wheat had the highest total N output compared to other crops. Higher total N output from spring wheat resulted in the non-significant difference in total N output among crop rotations in all years. Lower crop N removal reduced total N output in 2021 compared to other years.
Nitrogen loss to the environment through various processes out of total N input (Nle) ranged from 13% for pea in 2024 to 34% for spring wheat in 2022 and 2024 (Table 7). When accounting for both crop phases in a rotation, N loss ranged from 22% for pea–spring wheat in 2021 to 34% for spring wheat–spring wheat in 2022 and 2024. These values are lower than environmental N losses of 20–55% of the total N input for various cropping systems reported in the literature [11,12,13,14]. Variations in soil and climatic factors and management practices may have resulted in differences in Nle among cropping systems in various regions. Limited precipitation, lower rates of N fertilizer applied to small grains and pulse crops compared to other cereal crops, and dryland cropping systems without irrigation may have resulted in lower Nle values for this study compared to other cropping systems, which received higher N fertilization rates, adequate irrigation supply, and abundant precipitation. While increased N loss relative to total N output may have increased Nle for lentil compared to chickpea and pea in 2022 and for chickpea compared to lentil and pea in 2024, higher N fertilization rate likely increased Nle for spring wheat compared to pulse crops in all years. This resulted in the non-significant difference in Nle among crop rotations, although spring wheat–spring wheat had greater Nle than pulse crop–spring wheat rotations. This indicates that N fertilization to crops is one of the greatest sources of N loss to the environment.
4.3. Nitrogen Sequestration Rate
Changes in soil total N at 0–15 cm in October 2024 among crops and crop rotations were moderate, resulting in small values of N sequestration rate over a 4.5 yr period (Table 8). The greater soil total N for pea than lentil in 2024 was probably due to increased crop residue N returned to the soil, as biological N fixation was greater for pea than lentil (Table 1). It has been reported that straw N content is greater for pea than lentil [28]. Increased crop residue N returned to the soil can enhance soil total N [11,27,39]. This may have resulted in greater soil total N at 0–15 cm for pea–spring wheat than lentil–spring wheat in 2024 (Table 1). A reduction in soil total N from 2020 to 2024 resulted in negative N sequestration rates for crops and crop rotations, except for pea and pea–spring wheat, which had positive N sequestration rates due to increased soil total N in 2024 compared to 2021. Greater soil total N in 2024 may have resulted in higher N sequestration rates for pea and spring wheat than lentil and greater for pea–spring wheat and spring wheat–spring wheat than lentil–spring wheat.
4.4. Nitrogen Balance
Uncertainty in the values of some parameters for N inputs and outputs led to coefficient of variations for N balance ranging from 3 to 32% for crops and crop rotations (Table 9). These values are lower than 8–53% reported for dryland cropping systems in western North Dakota, USA, and western Canada [8,10,21]. Differences in soil and climatic conditions may have resulted in various coefficient of variation for N balance between this study and those in North Dakota and western Canada. Soils were mostly sandy loam to silt loam in North Dakota and western Canada compared to loam in this study. North Dakota and western Canada also receive 50 mm more precipitation than eastern Montana, USA. Coarse soil texture and higher precipitation may have resulted in greater N loss to the environment and, therefore, higher uncertainty in N balance values for studies conducted in North Dakota and western Canada than the site in this study. Variability in estimated values of N inputs can range from 5% for atmospheric N deposit to 50% for N outputs for environmental N losses [4,30].
Increased total N input and output led to greater N balance for pea and spring wheat than chickpea in 2021, but greater N input than output resulted in higher N balance for pea than spring wheat in 2023, because soil N sequestration rate was minimal among crops (Table 3, Table 8, and Table 9). Greater total N input but similar total N output resulted in higher N balance for chickpea than lentil and spring wheat in 2022. In contrast, lower total N input and output led to higher N balance for chickpea than other crops in 2024. Overall, this resulted in greater N balance for chickpea and pea than lentil and spring wheat. The positive N balance for pulse crops compared to the negative balance for spring wheat shows that pulse crops can result in N surplus compared to N deficit for spring wheat, and that chickpea and pea can have greater N surplus than lentil. Most of the N added to the soil from biological N fixation was probably retained more in the agroecosystems for pulse crops than spring wheat, where most of the N added from N fertilizers may have lost to the environment. The results were also concurrent for pulse crop–spring wheat rotations in the sense that chickpea–spring wheat and pea–spring wheat had positive N balances compared to other crop rotations and that these rotations had greater N balances than lentil–spring wheat. The results imply that chickpea and pea alone or in rotation with spring wheat reduced N loss to the environment by increasing N storage in crop residue and soil compared to continuous spring wheat. Our results are similar to those reported by numerous researchers [10,17,20,27] who observed that legume-based crop rotations showed neutral or positive N balance due to greater biological N fixation and lower N fertilization rate compared to continuous nonlegume cropping. Greater total N input than total output also resulted in a higher N balance in 2021 than in other years. Reduced crop N removal due to lower precipitation likely decreased total N output relative to total N input, resulting in higher N balance in 2021 than other years.
The N balance values of −25 kg N ha−1 for spring wheat to 32 kg N ha−1 for pea or −20 kg N ha−1 for lentil–spring wheat to 4 kg N ha−1 for pea–spring wheat rotations were between the values of −39 to to 45 kg N ha−1 of N balance reported for dryland cropping systems by various researchers in US, Canada, and Europe [10,17,19,40,41,42]. Several researchers [42,43] have suggested that most of N balance occurred at the expense of changes in soil total N, which was highly variable among cropping systems. In this study, most of the N balance occurred due to the differences in total N input and output because N sequestration rates remained minor, except for lentil or lentil–spring wheat rotation.
5. Conclusions
The results of this study showed that chickpea and pea had N surplus compared to N deficit for spring wheat or near neutral N balances for chickpea–spring wheat and pea–spring wheat compared to negative N balances for other crop rotations. This was due to greater total N input compared to total N output for pea or lower total N input and output for chickpea compared to lentil and spring wheat, as N sequestration rates were minor for crops and crop rotations. The proportion of N loss to the environment to total N input was greater for spring wheat than pulse crops, indicating a greater N loss for spring wheat, probably due to higher N fertilization rate. Chickpea and pea alone or in rotation with spring wheat can result in N surplus compared to N deficit for continuous spring wheat, indicating lower N loss to the environment for pulse crops. Crop rotations that include legumes, such as pulse crops, not only can reduce N fertilization rate for subsequent crops by increasing biological N fixation but also decrease environmental impacts by reducing N leaching and gaseous N loss. As a result, future studies on pulse crops–spring wheat rotations should include pulse crops, such as chickpea and pea, to reduce N loss to the environment and sustain crop production. Because of the uncertainty of some N inputs and output parameters, further long-term studies in other locations may be needed to accurately determine N balance under dryland pulse crop–nonlegume rotations.
Funding
The funding for this project was provided by USDA-ARS, Pulse Crop Health Initiative (No. 3032-05-10).
Data Availability Statement
Data is contained within the article.
Acknowledgments
I sincerely acknowledge the help and support provided by Michael Johnson, Chloe Turner-Meservy, and Wayne Adkins for field plot management and for Chloe Turner-Meservy, Nancy Webb, Courtney Hoffman, Dora Alvarez, Magaret Duffy, and Connie Tabbert for data collection in the field and analysis in the laboratory. I also acknowledge funding for this project from USDA-ARS, Pulse Crop Health Initiative (No. 3032-05-10). Mention of trade names or commercial products in this publication is solely for the purpose of providing specific information and does not imply recommendation or endorsement by the USDA. The USDA is an equal opportunity employer.
Conflicts of Interest
The author declare no conflict of interest.
References
- Erisman, J.W.; Galloway, J.N.; Seitzinger, S.; Bleeker, A.; Dise, N.B.; Petrescue, A.M.R.; Leach, A.M.; de Vries, W. Consequences of human modification of the global nitrogen cycle. Philos. Trans. R. Soc. B 2013, 368, e20130116. [Google Scholar] [CrossRef]
- Lee, J.; Necpalova, M.; Francesca, J.; Johan, S. Simulation of a regional soil nitrogen balance in Swiss croplands. Nutr. Cycl. Agroecosyst. 2020, 118, 9–22. [Google Scholar] [CrossRef]
- Sabota, M.A.; Ketterings, Q.M.; Compton, J.E.; McCrackin, M.I.; Singh, S. Cost of reactive nitrogen release from human activities to the environment in the U.S. Environ. Res. Lett. 2015, 10, e025006. [Google Scholar] [CrossRef]
- Meisinger, J.J.; Randall, G.W. Estimating nitrogen budgets for soil-crop systems. In Managing Nitrogen for Groundwater Quality and Farm Profitability; Follett, R.F., Ed.; Soil Science Society of America: Madison, WI, USA, 1991; pp. 85–124. [Google Scholar] [CrossRef]
- Schepers, J.S.; Mosier, A.R. Accounting for nitrogen in nonequilibrium soil-crop systems. In Managing Nitrogen for Groundwater Quality and Farm Profitability; Follett, R.F., Ed.; Soil Science Society of America: Madison, WI, USA, 1991; pp. 125–137. [Google Scholar] [CrossRef]
- Wang, C.; Dannenmann, M.; Meier, R.; Butterbach-Bahl, K. Inhibitory and side effects of acetylene and sodium chlorate on gross nitrification, gross ammonification, and soil-atmosphere exchange of N2O and CH4 in acidic to neutral montane grassland soil. Eur. J. Soil Biol. 2014, 65, 7–14. [Google Scholar] [CrossRef]
- Smil, V. Nitrogen in crop production: An account of global flows. Glob. Biogeochem. Cycle 1999, 13, 647–662. [Google Scholar] [CrossRef]
- Janzen, H.H.; Beauchemin, K.A.; Bruinsma, Y.; Campbell, C.A.; Desjardins, R.L.; Ellert, B.H.; Smith, E.C. The fate of nitrogen in agroecosystems: An illustration using Canadian estimates. Nutr. Cycl. Agroecosyst. 2003, 67, 85–102. [Google Scholar] [CrossRef]
- Eickhout, B.; Bouwman, A.P.; van Zeijts, H. The role of nitrogen in world food production and environmental sustainability. Agric. Ecosyst. Environ. 2006, 116, 4–14. [Google Scholar] [CrossRef]
- Ross, S.M.; Izaurralde, R.C.; Janzen, H.H.; Robertson, J.A.; McGill, W.B. The nitrogen balance of three long-term agroecosystems on a boreal soil in western Canada. Agric. Ecosyst. Environ. 2008, 127, 241–250. [Google Scholar] [CrossRef]
- Bremer, E.; Janzen, H.H.; Ellert, B.H.; McKenzie, R.H. Carbon, nitrogen, and greenhouse gas balance in an 18-year cropping system. Soil Sci. Soc. Am. J. 2011, 75, 1493–1502. [Google Scholar] [CrossRef]
- Gardner, J.B.; Drinkwater, L.E. The fate of nitrogen in grain cropping systems: A meta-analysis of 15N field experiments. Ecol. Appl. 2009, 19, 2167–2184. [Google Scholar] [CrossRef] [PubMed]
- Rong, Y.; Shiyang, C. Nitrogen losses in desert oasis agroecosystem in China estimated using a nitrogen balance approach. Soil Sci. Plant Nutr. 2021, 67, 197–205. [Google Scholar] [CrossRef]
- Zheng, M.M.; Zheng, H.; Wu, Y.X.; Xiao, X.; Du, Y.H.; Xu, W.H.; Lu, F.; Wang, K.K.; Ouyang, Z.Y. Changes in nitrogen budget and potential risk to the environment over 20 years in the agroecosystem of Haihe Basin, China. J. Environ. Sci. 2015, 28, 195–202. [Google Scholar] [CrossRef]
- Franzluebbers, A.J. Integrated crop-livestock systems in the southeastern USA. Agron. J. 2007, 99, 361–372. [Google Scholar] [CrossRef]
- Herrero, M.; Thorton, P.K.; Notenbaert, A.M.; Wood, S.; Masangi, S.; Freeman, H.A.; Bossio, D.; Dixon, J.; Peters, M.; van de Steeg, J.; et al. Smart investments in sustainable food productions: Revisiting mixed crop-livestock systems. Science 2010, 327, 822–825. [Google Scholar] [CrossRef]
- Pieri, L.; Ventura, F.; Vignudelli, M.; Rossi, P. Nitrogen balance in a hilly semi-agricultural watershed in northern Italy. Ital. J. Agron. 2011, 6, 67–75. [Google Scholar] [CrossRef]
- Sainju, U.M.; Stevens, W.B.; Caesar-Tonthat, T.; Montagne, C. Nitrogen dynamics affected by management practices in croplands transitioning from conservation reserve program. Agron. J. 2014, 106, 1677–1689. [Google Scholar] [CrossRef]
- Drinkwater, L.E.; Wagoneer, P.; Sarrantonio, M. Legume-based cropping systems have reduced carbon and nitrogen losses. Nature 1998, 396, 262–265. [Google Scholar] [CrossRef]
- Novelli, L.E.; Caviglia, O.P.; Jobbagy, E.G.; Sadras, V.O. Diversified crop sequences to reduce soil nitrogen mining in agroecosystems. Agric. Ecosyst. Environ. 2023, 341, e108208. [Google Scholar] [CrossRef]
- Sainju, U.M.; Ghimire, R.; Pradhan, G.P. Improving dryland cropping system nitrogen balance with no-tillage and nitrogen fertilization. J. Plant Nutrit. Soil Sci. 2019, 182, 374–384. [Google Scholar] [CrossRef]
- Watson, C.A.; Atkinson, D. Using nitrogen budgets to indicate nitrogen-use efficiency and losses from whole farm systems: A comparison of three methodological approaches. Nutr. Cycl. Agroecosyst. 1999, 53, 259–267. [Google Scholar] [CrossRef]
- McLellan, E.L.; Cassman, K.G.; Eagle, A.J.; Woodbury, P.B.; Sela, S.; Tonitto, C.; Marjerison, R.D.; van Es, H.M. The nitrogen balancing act: Tracking the environmental perspective of food production. Bioscience 2018, 68, 194–203. [Google Scholar] [CrossRef] [PubMed]
- Snyder, C.S.; Davidson, E.A.; Smith, P.; Venterea, R.T. Agriculture: Sustainable crop and animal production to help mitigate nitrous oxide emissions. Curr. Opin. Environ. Sustain. 2014, 9, 46–54. [Google Scholar] [CrossRef]
- Kehoe, E.; Rubio, G.; Salvagiotti, F. Biological nitrogen fixation in pea and vetch: Contribution and belowground structures to the partial nitrogen balance. Field Crops Res. 2024, 316, 109514. [Google Scholar] [CrossRef]
- Groffman, P.M.; House, G.J.; Hendrix, P.F.; Scott, D.E.; Crossley, D.A., Jr. Nitrogen cycling as affected by interaction of components in a Georgia Piedmont agroecosystem. Ecology 1986, 67, 80–87. [Google Scholar] [CrossRef]
- Blessler, A.; Blesh, J. A grass-legume cover crop maintains nitrogen inputs and nitrous oxide flushes from an organic agroecosystem. Ecosphere 2023, 14, e4428. [Google Scholar] [CrossRef]
- Sainju, U.M. Growth, yield, and quality of pulse crops and succeeding spring wheat in the rotation. Agron. J. 2025, 117, e70224. [Google Scholar] [CrossRef]
- Smucker, A.J.M.; McBurney, S.L.; Srivastava, A.K. Quantitative separation of roots from compacted soil profile by hydropneumatic elutriation system. Agron. J. 1982, 74, 500–503. [Google Scholar] [CrossRef]
- Sainju, U.M. Determination of nitrogen balance in agroecosystems. MethodsX 2017, 4, 199–208. [Google Scholar] [CrossRef]
- Stevenson, F.J. Origin and distribution of nitrogen in soils. In Nitrogen in Agricultural Soils; Stevenson, F.J., Ed.; Agronomy Monograph; Soil Science Society of America: Madison, WI, USA, 1982; Volume 22, pp. 1–42. [Google Scholar] [CrossRef]
- Migliorati, M.D.A.; Bell, M.J.; Grace, P.R.; Rowlings, D.W.; Scheer, C.; Strazzabosco, A. Assessing agronomic and environmental implications of different N fertilization strategies in subtropical grain cropping systems on Oxisols. Nutr. Cycl. Agroecosyst. 2014, 100, 369–382. [Google Scholar] [CrossRef]
- Delgado, J.A.; Shaffer, M.J.; Lal, H.; McKinney, S.P.; Gross, C.M.; Cover, H. Assessment of nitrogen losses to the environment with a Nitrogen Trading Tool (NTT). Comp. Electron. Agric. 2008, 63, 193–206. [Google Scholar] [CrossRef]
- Legg, J.O.; Meisinger, J.J. Soil nitrogen budgets. In Nitrogen in Agricultural Soils; Stevenson, F.J., Ed.; Agronomy Monograph; Soil Science Society of America: Madison, WI, USA, 1982; Volume 22, pp. 503–566. [Google Scholar] [CrossRef]
- Intergovernment Panel on Climate Change (IPCC). Climate Change 2014: Synthesis Report. Contribution of Working Groups I, II and III to the Fifth Assessment Report of the Intergovernmental Panel on Climate Change; IPCC: Geneva, Switzerland, 2014. [Google Scholar] [CrossRef]
- Littell, R.C.; Milliken, G.A.; Stroup, W.W.; Wolfinger, R.D.; Schabenberger, O. SAS for Mixed Models; SAS Inst. Inc.: Cary, NC, USA, 2016. [Google Scholar] [CrossRef]
- Lenssen, A.W.; Johnson, G.D.; Carlson, G.R. Cropping sequence and tillage system influences annual crop production and water use in semiarid Montana, USA. Field Crops Res. 2007, 100, 32–43. [Google Scholar] [CrossRef]
- Miller, P.R.; Bekkerman, A.; Jones, C.A.; Burgess, M.H.; Holmes, J.A.; Engel, R.E. Pea in rotation with wheat reduced uncertainty of economic returns in southwest Montana. Agron. J. 2015, 107, 541–550. [Google Scholar] [CrossRef]
- Sainju, U.M. Tillage, cropping sequence, and nitrogen fertilization influence dryland soil nitrogen. Agron. J. 2013, 105, 1253–1263. [Google Scholar] [CrossRef]
- Poudel, D.D.; Horwath, W.R.; Mitchell, J.P.; Temple, S.R. Impact of cropping systems on soil nitrogen storage and loss. Agric. Syst. 2001, 68, 253–268. [Google Scholar] [CrossRef]
- Davis, R.L.; Patton, J.J.; Teal, R.K.; Tang, Y.; Humphreys, M.T.; Mosali, J.; Girma, K.; Lawles, J.W.; Moges, S.M.; Malapati, A.; et al. Nitrogen balance in the Magruder plots following 109 years in continuous winter wheat. J. Plant Nutr. 2003, 8, 1561–1580. [Google Scholar] [CrossRef]
- Karrison, L.O.T.; Andren, O.; Katterer, T.; Mattison, I. Management effects on topsoil carbon and nitrogen in Swedish long-term experiments: Budget calculations with and without humus pool dynamics. Eur. J. Agron. 2003, 20, 137–147. [Google Scholar] [CrossRef]
- Korsaeth, A.; Eltun, R. Nitrogen mass balances in conventional, integrated, and ecological cropping systems and the relationship between balance calculations and nitrogen runoff in an 8-year field experiment in Norway. Agric. Ecosyst. Environ. 2000, 79, 199–214. [Google Scholar] [CrossRef]
Table 1.
Effect of pulse crop, spring wheat, pulse crop–spring wheat rotation, and year on the N fertilizer amount applied to spring wheat (Na) and biological N fixation (Nb). Sources of variance are CO, crop; RT, crop rotation; and YR, year.
Table 1.
Effect of pulse crop, spring wheat, pulse crop–spring wheat rotation, and year on the N fertilizer amount applied to spring wheat (Na) and biological N fixation (Nb). Sources of variance are CO, crop; RT, crop rotation; and YR, year.
| Crop | N Fertilizer Amount (Na) (kg N ha−1) --------------------------------------------------------- | Biological N Fixation (Nb) (kg N ha−1) ------------------------------------------------------------ | ||||||||
|---|---|---|---|---|---|---|---|---|---|---|
| 2021 | 2022 | 2023 | 2024 | Mean | 2021 | 2022 | 2023 | 2024 | Mean | |
| Chickpea | 5b a | 5b | 5b | 5b | 5b | 54.9a | 83.7a | 69.1b | 36.0b | 60.9c |
| Lentil | 5b | 5b | 5b | 5b | 5b | 56.7a | 64.0b | 82.3a | 104.1a | 76.8b |
| Pea | 5b | 5b | 5b | 5b | 5b | 65.3a | 80.2a | 77.3ab | 110.9a | 83.4a |
| Spring wheat | 73a | 52a | 67a | 69a | 65a | 0.0b | 0.0c | 0.0c | 0.0c | 0.0d |
| Significance | p values-------------------------------------------------------------------------------------------------------------- | |||||||||
| CO | <0.001 | <0.001 | ||||||||
| YR | <0.001 | <0.001 | ||||||||
| CO × YR | <0.001 | <0.001 | ||||||||
| Crop rotation | ||||||||||
| Chickpea–spring wheat | 39b b | 30 | 39b | 39 | 37b | 27.4a | 41.8a | 34.6b | 18.0b | 30.5b |
| Lentil–spring wheat | 39b | 26 | 34b | 37 | 34b | 28.4a | 32.0b | 41.1a | 52.1a | 38.4a |
| Pea–spring wheat | 39b | 29 | 33b | 38 | 35b | 32.6a | 40.0a | 38.7ab | 55.4a | 41.7a |
| Spring wheat–spring wheat | 73a | 50 | 72a | 65 | 65a | 0.0b | 0.0c | 0.0c | 0.0c | 0.0c |
| Significance | p values-------------------------------------------------------------------------------------------------------------- | |||||||||
| RT | 0.005 | 0.005 | ||||||||
| YR | 0.464 | 0.857 | ||||||||
| RT × YR | 0.009 | 0.009 | ||||||||
a Numbers followed by different letters within a column in a set are significantly different at p ≤ 0.05 by the least square means test. b Amount of N fertilizer applied to spring wheat following pulse crops.
Table 2.
Effect of pulse crop, spring wheat, pulse crop–spring wheat rotation, and year on soil N mineralization at the 0–15 cm depth (Nc) and crop seed N (Ne). Sources of variance are CO, crop; RT, crop rotation; and YR, year.
Table 2.
Effect of pulse crop, spring wheat, pulse crop–spring wheat rotation, and year on soil N mineralization at the 0–15 cm depth (Nc) and crop seed N (Ne). Sources of variance are CO, crop; RT, crop rotation; and YR, year.
| Crop | Soil N Mineralization (Nc) (kg N ha−1) --------------------------------------------------------- | Crop Seed N (Ne) (kg N ha−1) ------------------------------------------------------------ | ||||||||
|---|---|---|---|---|---|---|---|---|---|---|
| 2021 | 2022 | 2023 | 2024 | Mean | 2021 | 2022 | 2023 | 2024 | Mean | |
| Chickpea | 31.8 | 24.6 | 31.2 | 27.6 | 28.8 | 6.8a a | 6.8a | 6.8a | 6.8a | 6.8a |
| Lentil | 32.8 | 24.2 | 30.4 | 24.5 | 27.9 | 2.7b | 2.7b | 2.7b | 2.7b | 2.7b |
| Pea | 31.9 | 25.5 | 31.8 | 26.8 | 29.0 | 7.4a | 7.4a | 7.4a | 7.4a | 7.4a |
| Spring wheat | 32.0 | 24.6 | 32.1 | 34.6 | 28.3 | 2.2b | 2.2b | 2.2b | 2.2b | 2.2b |
| Significance | p values-------------------------------------------------------------------------------------------------------------- | |||||||||
| CO | 0.642 | <0.001 | ||||||||
| YR | <0.001 | 1.000 | ||||||||
| CO × YR | 0.689 | <0.001 | ||||||||
| Crop rotation | ||||||||||
| Chickpea–spring wheat | 31.8 | 23.8 | 31.4 | 26.6 | 28.4 | 4.5a | 4.5a | 4.5a | 4.5a | 4.5a |
| Lentil–spring wheat | 25.2 | 31.4 | 24.3 | 33.3 | 27.8 | 2.5b | 2.5b | 2.5b | 2.5b | 2.5b |
| Pea–spring wheat | 33.3 | 25.1 | 32.6 | 24.9 | 29.0 | 4.8a | 4.8a | 4.8a | 4.8a | 4.8a |
| Spring wheat–spring wheat | 33.9 | 24.8 | 31.1 | 25.5 | 28.8 | 2.2b | 2.2b | 2.2b | 2.2b | 2.2b |
| Significance | p values-------------------------------------------------------------------------------------------------------------- | |||||||||
| RT | 0.264 | <0.001 | ||||||||
| YR | <0.001 | 1.000 | ||||||||
| RT × YR | 0.318 | <0.001 | ||||||||
a Numbers followed by different letters within a column in a set are significantly different at p ≤ 0.05 by the least square means test.
Table 3.
Effect of pulse crop, spring wheat, pulse crop-spring wheat rotation, and year on total N input and output. Sources of variance are CO, crop; RT, crop rotation; and YR, year.
Table 3.
Effect of pulse crop, spring wheat, pulse crop-spring wheat rotation, and year on total N input and output. Sources of variance are CO, crop; RT, crop rotation; and YR, year.
| Crop | Total N Input (kg N ha−1) --------------------------------------------------------- | Total N Output (kg N ha−1) ------------------------------------------------------------ | ||||||||
|---|---|---|---|---|---|---|---|---|---|---|
| 2021 | 2022 | 2023 | 2024 | Mean | 2021 | 2022 | 2023 | 2024 | Mean | |
| Chickpea | 110.4ab a | 132.0a | 124.1ab | 87.4d | 113.5c | 72.9b | 111.9a | 94.8b | 43.3b | 80.7c |
| Lentil | 109.2b | 107.9b | 132.4a | 148.3b | 124.4b | 72.5b | 85.4b | 110.0b | 142.4a | 102.6b |
| Pea | 121.6a | 130.1a | 133.5a | 162.0a | 136.8a | 78.9ab | 108.6a | 103.3b | 114.5a | 108.9b |
| Spring wheat | 119.2ab | 90.1c | 112.8b | 107.8c | 107.5d | 92.6a | 125.3a | 157.2a | 148.9a | 131.0a |
| Significance | p values-------------------------------------------------------------------------------------------------------------- | |||||||||
| CO | <0.001 | <0.001 | ||||||||
| YR | <0.001 | <0.001 | ||||||||
| CO × YR | <0.001 | <0.001 | ||||||||
| Crop rotation | ||||||||||
| Chickpea–spring wheat | 114.7ab | 112.1a | 120.9 | 100.1b | 112.0b | 82.6 | 120.5 | 123.2 | 95.6 | 105.5 |
| Lentil–spring wheat | 112.0b | 97.6ab | 120.5 | 127.3a | 114.4ab | 82.0 | 108.6 | 138.4 | 147.1 | 119.0 |
| Pea–spring wheat | 121.8a | 110.9a | 120.5 | 134.7a | 122.0a | 85.6 | 115.5 | 137.0 | 150.8 | 122.2 |
| Spring wheat–spring wheat | 121.1a | 89.0b | 117.3 | 104.7b | 108.0b | 94.6 | 117.8 | 139.8 | 138.8 | 122.8 |
| Significance | p values-------------------------------------------------------------------------------------------------------------- | |||||||||
| RT | 0.036 | 0.081 | ||||||||
| YR | 0.002 | <0.001 | ||||||||
| RT × YR | 0.022 | 0.123 | ||||||||
a Numbers followed by different letters within a column in a set are significantly different at p ≤ 0.05 by the least square means test.
Table 4.
Effect of pulse crop, spring wheat, pulse crop–spring wheat rotation, and year on crop N removal (Ng) and ammonia volatilization (Nh). Sources of variance are CO, crop; RT, crop rotation; and YR, year.
Table 4.
Effect of pulse crop, spring wheat, pulse crop–spring wheat rotation, and year on crop N removal (Ng) and ammonia volatilization (Nh). Sources of variance are CO, crop; RT, crop rotation; and YR, year.
| Crop | Crop N Removal (Ng) (kg N ha−1) --------------------------------------------------------- | Ammonia Volatilization (Nh) (kg N ha−1) ------------------------------------------------------------ | ||||||||
|---|---|---|---|---|---|---|---|---|---|---|
| 2021 | 2022 | 2023 | 2024 | Mean | 2021 | 2022 | 2023 | 2024 | Mean | |
| Chickpea | 55.3 | 92.4ab a | 76.1b | 27.0b | 62.7c | 0.8b | 0.8b | 0.8b | 0.8b | 0.8b |
| Lentil | 55.1 | 67.6b | 90.8b | 121.3a | 83.7b | 0.8b | 0.8b | 0.8b | 0.8b | 0.8b |
| Pea | 60.9 | 89.6ab | 84.3b | 123.3a | 89.4ab | 0.8b | 0.8b | 0.8b | 0.8b | 0.8b |
| Spring wheat | 57.5 | 94.4a | 120.6a | 112.3a | 96.3a | 11.0a | 7.7a | 10.0a | 10.4a | 9.8a |
| Significance | p values-------------------------------------------------------------------------------------------------------------- | |||||||||
| CO | <0.001 | <0.001 | ||||||||
| YR | <0.001 | <0.001 | ||||||||
| CO × YR | <0.001 | <0.001 | ||||||||
| Crop rotation | ||||||||||
| Chickpea–spring wheat | 56.5 | 94.6 | 95.5 | 68.9b | 78.3b | 5.9 | 4.6 | 5.8 | 5.9 | 5.5b |
| Lentil–spring wheat | 55.6 | 84.9 | 110.5 | 118.5a | 92.8a | 5.9 | 4.0 | 5.1 | 5.5 | 5.1b |
| Pea–spring wheat | 58.7 | 90.1 | 109.3 | 121.1a | 95.3a | 5.9 | 4.4 | 4.9 | 5.7 | 5.2b |
| Spring wheat–spring wheat | 59.2 | 87.5 | 102.9 | 103.1a | 88.7ab | 11.0 | 7.5 | 10.8 | 9.8 | 9.8a |
| Significance | p values-------------------------------------------------------------------------------------------------------------- | |||||||||
| RT | 0.039 | 0.005 | ||||||||
| YR | <0.001 | 0.389 | ||||||||
| RT × YR | 0.033 | 0.999 | ||||||||
a Numbers followed by different letters within a column in a set are significantly different at p ≤ 0.05 by the least square means test.
Table 5.
Effect of pulse crop, spring wheat, pulse crop–spring wheat rotation, and year on N loss due to denitrification (Ni) and plant senescence (Nj). Sources of variance are CO, crop; RT, crop rotation; and YR, year.
Table 5.
Effect of pulse crop, spring wheat, pulse crop–spring wheat rotation, and year on N loss due to denitrification (Ni) and plant senescence (Nj). Sources of variance are CO, crop; RT, crop rotation; and YR, year.
| Crop | Denitrification N Loss (Ni) (kg N ha−1) --------------------------------------------------------- | Plant Senescence N Loss (Nj) (kg N ha−1) ------------------------------------------------------------ | ||||||||
|---|---|---|---|---|---|---|---|---|---|---|
| 2021 | 2022 | 2023 | 2024 | Mean | 2021 | 2022 | 2023 | 2024 | Mean | |
| Chickpea | 1.5b a | 1.5b | 1.5b | 1.5b | 1.5b | 3.1 | 5.0a | 4.2b | 1.7b | 3.5c |
| Lentil | 1.5b | 1.5b | 1.5b | 1.5b | 1.5b | 3.1 | 3.5b | 5.0b | 6.6a | 4.5b |
| Pea | 1.5b | 1.5b | 1.5b | 1.5b | 1.5b | 3.9 | 4.9a | 4.9b | 7.1a | 5.2a |
| Spring wheat | 9.0a | 6.6a | 8.3a | 8.5a | 8.0a | 3.3 | 5.2a | 6.5a | 6.3a | 5.3a |
| Significance | p values-------------------------------------------------------------------------------------------------------------- | |||||||||
| CO | <0.001 | <0.001 | ||||||||
| YR | <0.001 | <0.001 | ||||||||
| CO × YR | <0.001 | <0.001 | ||||||||
| Crop rotation | ||||||||||
| Chickpea–spring wheat | 5.3 | 4.3 | 5.2 | 5.3 | 5.0b | 3.2 | 5.2 | 3.9b | 3.2b | 4.4b |
| Lentil–spring wheat | 5.3 | 3.8 | 4.7 | 5.0 | 4.7b | 3.2 | 4.5 | 6.0a | 6.5a | 5.1a |
| Pea–spring wheat | 5.3 | 4.2 | 4.5 | 5.1 | 4.7b | 3.6 | 5.0 | 5.0ab | 6.1a | 5.4a |
| Spring wheat–spring wheat | 9.0 | 6.4 | 8.9 | 8.1 | 8.1a | 3.4 | 4.9 | 5.6a | 5.9a | 4.9ab |
| Significance | p values-------------------------------------------------------------------------------------------------------------- | |||||||||
| RT | 0.005 | 0.013 | ||||||||
| YR | 0.381 | <0.001 | ||||||||
| RT × YR | 0.999 | 0.017 | ||||||||
a Numbers followed by different letters within a column in a set are significantly different at p ≤ 0.05 by the least square means test.
Table 6.
Effect of pulse crop, spring wheat, pulse crop–spring wheat rotation, and year on N loss due to leaching (Nk) and gas emissions (Nl). Sources of variance are CO, crop; RT, crop rotation; and YR, year.
Table 6.
Effect of pulse crop, spring wheat, pulse crop–spring wheat rotation, and year on N loss due to leaching (Nk) and gas emissions (Nl). Sources of variance are CO, crop; RT, crop rotation; and YR, year.
| Crop | Leaching N Loss (Nk) (kg N ha−1) --------------------------------------------------------- | Gaseous N Loss (Nl) (kg N ha−1) ------------------------------------------------------------ | ||||||||
|---|---|---|---|---|---|---|---|---|---|---|
| 2021 | 2022 | 2023 | 2024 | Mean | 2021 | 2022 | 2023 | 2024 | Mean | |
| Chickpea | 10.0b a | 10.0b | 10.0b | 10.0b | 10.0b | 0.1b | 0.1b | 0.1b | 0.1b | 0.1b |
| Lentil | 10.0b | 10.0b | 10.0b | 10.0b | 10.0b | 0.1b | 0.1b | 0.1b | 0.1b | 0.1b |
| Pea | 10.0b | 10.0b | 10.0b | 10.0b | 10.0b | 0.1b | 0.1b | 0.1b | 0.1b | 0.1b |
| Spring wheat | 12.0a | 12.0a | 12.0a | 12.0a | 12.0a | 1.10a | 0.78a | 1.00a | 1.05a | 0.98a |
| Significance | p values-------------------------------------------------------------------------------------------------------------- | |||||||||
| CO | <0.001 | <0.001 | ||||||||
| YR | <0.905 | <0.001 | ||||||||
| CO × YR | <0.001 | <0.001 | ||||||||
| Crop rotation | ||||||||||
| Chickpea–spring wheat | 11.0 | 11.0 | 11.0 | 11.0 | 11.0a | 0.6 | 0.5 | 0.6 | 0.6 | 0.6b |
| Lentil–spring wheat | 11.0 | 11.0 | 11.0 | 11.0 | 11.0a | 0.6 | 0.4 | 0.5 | 0.6 | 0.5b |
| Pea–spring wheat | 11.0 | 11.0 | 11.0 | 11.0 | 11.0a | 0.6 | 0.5 | 0.5 | 0.6 | 0.5b |
| Spring wheat–spring wheat | 12.0 | 12.0 | 12.0 | 12.0 | 10.0b | 1.1 | 0.8 | 1.1 | 1.0 | 1.0a |
| Significance | p values-------------------------------------------------------------------------------------------------------------- | |||||||||
| RT | 0.005 | 0.003 | ||||||||
| YR | 1.000 | 0.392 | ||||||||
| RT × YR | 1.000 | 0.999 | ||||||||
a Numbers followed by different letters within a column in a set are significantly different at p ≤ 0.05 by the least square means test.
Table 7.
Effect of pulse crop, spring wheat, pulse crop–spring wheat rotation, and year on N loss due to surface runoff (Nm) and N loss to the environment/total N input ratio (Nle). Sources of variance are CO, crop; RT, crop rotation; and YR, year.
Table 7.
Effect of pulse crop, spring wheat, pulse crop–spring wheat rotation, and year on N loss due to surface runoff (Nm) and N loss to the environment/total N input ratio (Nle). Sources of variance are CO, crop; RT, crop rotation; and YR, year.
| Crop | Surface Runoff N Loss (Nm) (kg N ha−1) --------------------------------------------------------- | Nle (%) ------------------------------------------------------------ | ||||||||
|---|---|---|---|---|---|---|---|---|---|---|
| 2021 | 2022 | 2023 | 2024 | Mean | 2021 | 2022 | 2023 | 2024 | Mean | |
| Chickpea | 0.1b a | 0.1b | 0.1b | 0.1b | 0.1b | 15.9b | 15.0c | 15.0b | 18.7b | 16.1b |
| Lentil | 0.1b | 0.1b | 0.1b | 0.1b | 0.1b | 16.0b | 16.7b | 14.6b | 14.1c | 15.4c |
| Pea | 0.1b | 0.1b | 0.1b | 0.1b | 0.1b | 15.0b | 15.0c | 14.4b | 13.3c | 14.4d |
| Spring wheat | 0.7a | 0.5a | 0.7a | 0.7a | 0.6a | 29.4a | 34.1a | 32.3a | 34.3a | 32.5a |
| Significance | p values-------------------------------------------------------------------------------------------------------------- | |||||||||
| CO | <0.001 | <0.001 | ||||||||
| YR | <0.001 | <0.001 | ||||||||
| CO × YR | <0.001 | <0.001 | ||||||||
| Crop rotation | ||||||||||
| Chickpea–spring wheat | 0.4 | 0.4 | 0.4 | 0.4 | 0.4b | 22.7 | 24.8 | 23.5 | 26.1 | 24.3b |
| Lentil–spring wheat | 0.4 | 0.4 | 0.4 | 0.4 | 0.4b | 23.2 | 25.4 | 23.8 | 24.4 | 24.2b |
| Pea–spring wheat | 0.4 | 0.4 | 0.4 | 0.4 | 0.4b | 21.9 | 24.4 | 23.6 | 24.2 | 23.5b |
| Spring wheat–spring wheat | 0.7 | 0.5 | 0.7 | 0.7 | 0.7a | 29.1 | 33.8 | 31.6 | 33.8 | 32.0a |
| Significance | p values-------------------------------------------------------------------------------------------------------------- | |||||||||
| RT | 0.004 | 0.012 | ||||||||
| YR | 0.408 | 0.596 | ||||||||
| RT × YR | 0.999 | 1.000 | ||||||||
a Numbers followed by different letters within a column in a set are significantly different at p ≤ 0.05 by the least square means test.
Table 8.
Effect of pulse crop and spring wheat, pulse crop–spring wheat rotation, and year on soil total N and N sequestration rate at the 0–15 cm depth.
Table 8.
Effect of pulse crop and spring wheat, pulse crop–spring wheat rotation, and year on soil total N and N sequestration rate at the 0–15 cm depth.
| Crop | Soil Total N (kg N ha−1) ---------------------------------------- | N Sequestration Rate (kg N ha−1 yr−1) | |
|---|---|---|---|
| April 2020 | October 2024 | ||
| Chickpea | 2688 | 2671ab a | −3.8ab |
| Lentil | 2688 | 2621b | −14.9b |
| Pea | 2688 | 2705a | 3.8a |
| Spring wheat | 2688 | 2681ab | −1.6a |
| p value | 0.013 | 0.031 | |
| Crop rotation | |||
| Chickpea–spring wheat | 2688 | 2672ab a | −3.6ab |
| Lentil–spring wheat | 2688 | 2621b | −14.9b |
| Pea–spring wheat | 2688 | 2693a | 1.1a |
| Spring wheat–spring wheat | 2688 | 2685ab | −1.0a |
| p value | 0.021 | 0.022 | |
a Numbers followed by different letters within a column in a set are significantly different at p ≤ 0.05 by the least square means test.
Table 9.
Effect of pulse crop and spring wheat, pulse crop–spring wheat rotation, and year on N balance. Sources of variance are CO, crop; RT, crop rotation; and YR, year.
Table 9.
Effect of pulse crop and spring wheat, pulse crop–spring wheat rotation, and year on N balance. Sources of variance are CO, crop; RT, crop rotation; and YR, year.
| Crop | N Balance (kg N ha−1) ------------------------------------------------------------------------------------------------------------------ | ||||
|---|---|---|---|---|---|
| 2021 | 2022 | 2023 | 2024 | Mean | |
| Chickpea | 3.9 (±0.5)b | 46.4 (±8.0)a | −4.4 (±0.1)ab | 70.3 (±6.9)a | 29.0 (±5.3)a |
| Lentil | 10.8 (±3.6)ab | 18.6 (±3.8)b | −3.5 (±0.3)ab | 1.9 (±0.3)b | 7.0 (±1.9)b |
| Pea | 36.8 (±7.3)a | 35.0 (±5.4)ab | 24.4 (±4.8)a | 31.1 (±5.2)b | 31.9 (±4.2)a |
| Spring wheat | 37.6 (±2.9)a | −49.6 (±5.0)c | −33.4 (±5.0)b | −55.3 (±5.0)c | −25.1 (±6.2)c |
| Significance | p values-------------------------------------------------------------------------------------------------------- | ||||
| CO | <0.001 | ||||
| YR | 0.042 | ||||
| CO × YR | <0.001 | ||||
| Crop rotation | |||||
| Chickpea–spring wheat | 28.4 (±4.0)ab | −12.1 (±2.5) | −6.0 (±1.9)a | 0.8 (±0.2)a | 2.8 (±0.2)a |
| Lentil–spring wheat | 15.1 (±3.0)b | −25.6 (±5.7) | −32.9 (±5.3)b | −34.7 (±5.7)b | −19.6 (±3.3)b |
| Pea–spring wheat | 40.1 (±2.8)a | −0.7 (±0.1) | −12.7(±3.1)ab | −12.3 (±2.1)ab | 3.6 (±0.2)a |
| Spring wheat–spring wheat | 34.9 (±1.3)ab | −20.6 (±3.4) | −14.1 (±3.1)ab | −25.7 (±3.7)b | −6.4 (±0.9)ab |
| Significance | p values-------------------------------------------------------------------------------------------------------- | ||||
| RT | 0.025 | ||||
| YR | <0.001 | ||||
| RT × YR | 0.017 | ||||
Numbers followed by different letters within a column in a set are significantly different at p ≤ 0.05 by the least square means test.
Disclaimer/Publisher’s Note: The statements, opinions and data contained in all publications are solely those of the individual author(s) and contributor(s) and not of MDPI and/or the editor(s). MDPI and/or the editor(s) disclaim responsibility for any injury to people or property resulting from any ideas, methods, instructions or products referred to in the content. |
© 2026 by the author. Licensee MDPI, Basel, Switzerland. This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY) license.
Share and Cite
MDPI and ACS Style
Sainju, U.M. Nitrogen Balance for Pulse Crops in Rotation with Spring Wheat. Agronomy 2026, 16, 463. https://doi.org/10.3390/agronomy16040463
AMA Style
Sainju UM. Nitrogen Balance for Pulse Crops in Rotation with Spring Wheat. Agronomy. 2026; 16(4):463. https://doi.org/10.3390/agronomy16040463
Chicago/Turabian StyleSainju, Upendra M. 2026. "Nitrogen Balance for Pulse Crops in Rotation with Spring Wheat" Agronomy 16, no. 4: 463. https://doi.org/10.3390/agronomy16040463
APA StyleSainju, U. M. (2026). Nitrogen Balance for Pulse Crops in Rotation with Spring Wheat. Agronomy, 16(4), 463. https://doi.org/10.3390/agronomy16040463
Note that from the first issue of 2016, this journal uses article numbers instead of page numbers. See further details here.
