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Article

The Application of Slow-Release Nitrogen Combined with Soil Conditioner Under the Impact of Alkaline Salinity in Alfalfa Cultivation and Soil Improvement

by
Ping Liu
1,*,
Bo Wu
2,
Zichao Zhao
1,
Guoliang Wang
2 and
Zhaohui Liu
1,*
1
State Key Laboratory of Nutrient Use and Management, Key Laboratory of Agro-Environment of Huang-Huai-Hai Plain, Ministry of Agriculture and Rural Affairs, Institute of Agricultural Resources and Environment, Shandong Academy of Agricultural Sciences, Jinan 250100, China
2
Institute of Leisure Agriculture, Shandong Academy of Agricultural Sciences, Jinan 250100, China
*
Authors to whom correspondence should be addressed.
Agronomy 2025, 15(4), 923; https://doi.org/10.3390/agronomy15040923
Submission received: 10 March 2025 / Revised: 5 April 2025 / Accepted: 7 April 2025 / Published: 10 April 2025
(This article belongs to the Special Issue Responses of Forage Crops to Environmental Stresses and Stress Alleviating Strategies)
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Versions Notes

Abstract

:
Water-based resin-coated controlled-release fertilizer (CRF) is valued for its safety, environmental benefits, and water absorption/retention properties. To improve the productivity of alfalfa (Medicago sativa L.) and the soil quality in coastal saline–alkali land at the Yellow River Delta, in this work, we carried out field experiments to study how the application of CRF (water-based resin-coated urea) and soil conditioner, both developed in-house, affected the alfalfa harvest and the soil properties. The following five treatments were tested from 2022 to 2023: T0, no fertilization; T1, urea with P&K fertilizers; T2, CRF with P&K fertilizers; T3, urea, P&K fertilizers, and soil conditioner; T4, CRF, P&K fertilizers, and soil conditioner. The results showed that the simultaneous application of CRF and soil conditioner (i.e., T4) had the most obvious effect on improving the yield and quality of alfalfa. In 2022, T4 had 6.3% higher total alfalfa yield than T0. In 2023, T4 had 14.2% and 8.4% higher total alfalfa yield than T0 and T1, respectively. The alfalfa from T4 had higher crude protein content and relative feeding value (RFV), lower acid detergent fiber (ADF) and neutral detergent fiber (NDF) content. The combined application of CRF and soil conditioner reduced the salinity of the surface soil and increased the soil organic matter, available nitrogen, and phosphorus at the 0~40 cm layer. Therefore, the application of soil conditioner and CRF can improve the use of coastal saline–alkali land for the cultivation of alfalfa.

1. Introduction

Saline–alkali land, also known as salt-affected soil, is characterized by high concentrations of soluble salts and exchangeable sodium [1]. Such land is detrimental to plant growth as its poor structure and low permeability hinder the uptake of water and nutrients [2]. It is found on every continent and under almost all climatic conditions, although it is more prevalent in arid and semi-arid regions compared to humid areas [3]. In China, saline–alkali land amounts to about 37 million hectares, of which approximately 5 million hectares are coastal saline–alkali land [4]. The province of Shandong has abundant coastal saline–alkali land, mainly in the Yellow River Delta. Soil salinization is serious at the Yellow River Delta because of the low terrain, the poor drainage, the lateral infiltration of the Yellow River water, and the infiltration of seawater [5]. The province has been very active in the reclamation and utilization of the affected soils to boost agricultural productivity, and the successful reclamation projects have led to significant improvements in crop yields and economic returns for local farmers [6].
Alfalfa (Medicago sativa L.) is a high-quality perennial leguminous forage plant with high yield, high nutritional value, and wide adaptability [7]. With deep root systems, copious tillers, and extensive ground coverage, it can significantly reduce ground transpiration and surface water evaporation, thereby effectively reducing the saline–alkali content of the cultivated layer [8]. Planting alfalfa on saline–alkali soil not only has economic and ecological benefits but also efficiently utilizes and improves the land [9,10], but such land tends to produce alfalfa at lower yield with poorer quality [11]. Since alfalfa is a high-yield forage that can be harvested 2 to 5 times a year, it takes away much more nutrients from the soil than other forage crops. Kelling [12] estimated that, assuming an annual alfalfa yield of 10~15 t, each year, alfalfa removes 30~56 kg ha−1 of nitrogen, 26~40 kg ha−1 of phosphorus, and 200~270 kg ha−1 of potassium from the soil (the nitrogen fixation characteristics of alfalfa were already considered in the calculation). Hence, without proper fertilization, alfalfa cultivation will reduce soil fertility and productivity, especially for salinized soil that has low fertility and poor structure [13].
By regulating the dissolution rate of nutrients through physical and chemical means, such as coating, encapsulation, adding inhibitors, hydrogel integration, etc., controlled-release fertilizers (CRFs) supply nutrients to crops according to the demands at various growth stages [14]. Compared to traditional chemical fertilizers, CRFs reduce the volatilization of ammonium nitrogen and the leaching and denitrification of nitrate nitrogen [15]. They enhance crop yield and mitigate environmental problems related to the large-scale application of traditional chemical fertilizers, including nitrogen loss, soil nutrient imbalance, and water pollution [16]. Because they release nutrients slowly, CRFs have less impact on the soil salinity [17,18]. At present, CRFs are widely used in growing food and cash crops (e.g., wheat, rice, and cotton) in saline–alkali lands, but they have limited use in forage production [19,20,21]. Agriculture in these problematic environments is seriously restricted by shallow groundwater levels, high mineralization, and high soil salinity. A soil conditioner is a substance used to enhance the physical, chemical, and biological properties of soil, making it more suitable for plant growth without focusing primarily on nutrient provision. The application of soil conditioner is an effective measure to address these issues [22,23], but the efficacy of different types of conditioners varies greatly [24,25]. Suitable soil conditioners need to be developed according to the causes and characteristics of the challenging regions and screened accordingly.
Water-based resin-coated CRF uses water as a solvent or dispersant during the film-forming process, which eliminates the need for solvent recovery. With its features of safety, environmental friendliness, and water absorption/retention, it has emerged as a significant focus of CRF research in recent years [15]. In this study, alfalfa was grown on the coastal saline–alkali land of the Yellow River Delta, and the impact of CRF (water-based resin-coated urea) and soil conditioner, both developed in-house, on crop yield, crop quality, and soil amelioration was examined. The results could provide theoretical and technical support for improving alfalfa productivity and soil quality at coastal saline–alkali lands.

2. Materials and Methods

2.1. Test Site

The test was carried out at the Yellow River Delta modern agriculture experimental demonstration base of Shandong Academy of Agricultural Sciences (36°18′ N, 118°37′ E). The area is in the warm temperate zone and has a semi-humid continental monsoon climate with four distinct seasons. The annual temperature is 11.7~12.6 °C, the annual sunshine is 2590~2830 h, and the frost-free period is 211 days. The annual precipitation is 530~630 mm, 70% of which occurs in the summer, and the annual evapotranspiration is 750~2400 mm. The area features salinized tidal soil with uneven distribution of salinity and fertility. The soil was tested in layers of 20 cm because the tilling layer (the soil surface formed by long-term cultivation) is generally 15~20 cm thick and is clearly distinguished from the underlying layers. Table 1 lists the basic physicochemical properties of the 0~20 cm and 20~40 cm soil layers before the test.

2.2. Experimental Design

The CRF (water-based resin-coated urea) was developed in-house as follows: The solution of water-resistant resin in the acrylic monomer was mixed with a hydrogel containing modified cellulose, and emulsifier, crosslinking agent, and initiator were added. High-speed shear emulsification was performed to give a homogeneous emulsion, referred to as the water-based resin-coated emulsion. The emulsion was evenly sprayed onto the surface of large urea granules using a drum coating machine, and the coated granules were dried in a fluidized bed to develop a solidified film, thus giving the water-based resin-coated urea. The CRF had a nitrogen content of 43%. Other fertilizers used in this study included urea (44% N), calcium superphosphate (16%P2O5), and potassium sulfate (50%K2O), which were all purchased from Shikefeng Chemical Co., Ltd. (Linyi, China). The soil conditioner was developed in-house and contained 50% dry fermented cow dung, 20% biochar, 10% humic acid, 10% vermiculite, and 10% fermented bacterial residues. Biochar was purchased from Shandong Xiangba New Energy Co., Ltd. (Linyi, China), and the main raw materials were crop stalks and peanut shells. The other 4 ingredients were purchased from Shandong Yunhanda Agricultural Technology Co., Ltd. (Jinan, China). Its chemical properties were as follows: pH, 7.13; N content, 0.38%; P content (P2O5), 0.04%; K content (K2O), 2.39%; and organic matter, 32.16%.
The experiments adopted a completely randomized block design with three replications, and each plot (6 m × 10 m) was separated from its neighbor by 1 m. The alfalfa variety WL440 was sown in the spring of 2020 at a row spacing of 30 cm. The following five treatments were applied from 2022 to 2023: T0, no fertilization; T1, urea with P&K fertilizers; T2, CRF with P&K fertilizers; T3, urea, P&K fertilizers, and soil conditioner; T4, CRF, P&K fertilizers, and soil conditioner. The dosage of the fertilizers was 75-75-75 N/P2O5/K2O kg ha−1, and the dosage of the soil conditioner was 4500 kg ha−1.
During the green-up of alfalfa (on 16 March 2022 and 18 March 2023), ditches (18~20 cm depth) were dug in each plot between neighboring rows, and the fertilizers (along with the conditioner, if applicable) were mixed thoroughly and spread at the bottom evenly. The ditches were then backfilled, and spray irrigation was applied the next day. Fertilizers and conditioners were applied only once a year in the spring.

2.3. Harvest

Alfalfa was harvested 3 times in 2022 and 4 times in 2023 in the flowering stage, on 22 May, 3 August, and 16 October in 2022 (referred to as H1, H2, and H3) and, on 12 May, 20 July, 6 September, and 22 October in 2023 (referred to as H1, H2, H3, and H4). The stubble height was 5 cm. The fresh weight of the plants at the center of each plot (1 m2: 1.0 m × 1.0 m) was measured immediately after each harvest, and randomly chosen fresh grass (about 400 g) was brought back to the laboratory, baked at 105 °C for 30 min in an oven to kill the green, and then maintained at 65 °C until constant weight. The dry–fresh ratio was calculated to determine the hay yield per unit area. The dried alfalfa was kept for further analysis.

2.4. Forage Analysis

The dried alfalfa was finely ground and passed through a 1 mm sieve before analysis. The crude protein content was determined using the Kjeldahl method [26]. The neutral detergent fiber (NDF) and the acid detergent fiber (ADF) were determined using the Van Soest method [27]. The dry matter (DDM) and dry matter intake (DMI) were calculated from NDF and ADF, and the relative feed value (RFV) was estimated [28]:
DDM = 88.9 − 0.779 × ADF
DMI = 120/NDF
RFV = DMI × DDM/1.29

2.5. Soil Analysis

After the last harvest of 2023, soil samples were collected at 20, 40, and 60 cm depth between alfalfa rows using the core method. At each plot, for each soil layer, one specimen was collected at the center, and two specimens were collected at opposing corners, and, then, the three specimens were thoroughly mixed. After removing plant roots and debris, a portion of the fresh soil (about 150 g) was analyzed. The fresh soil was air-dried and passed through a 1 mm sieve, and the soil salinity (SS), soil organic matter (SOM), pH, available N (AN), available P (AP), and available K (AK) were determined according to the methods described by Bao [29].

2.6. Statistical Analysis

All data were analyzed using SPSS 22.0 and visualized using Sigma Plot 15.0. Mean values were compared using Duncan’s multiple range test. The effects of CRF and soil conditioner on alfalfa yield and soil properties were tested by one-way analysis of variance (ANOVA). The Pearson correlations between the alfalfa yield and the soil physicochemical properties were determined. Differences between groups were considered statistically significant when p < 0.05.

3. Results

3.1. Alfalfa Yield

Table 2 lists the alfalfa yield during the experiment. In 2022, the application of fertilizers and/or soil conditioners improved the alfalfa yield to some extent, but no significant difference in the alfalfa yield was found among the four treatments (T1~T4) for all three harvests (H1~H3). For H1, all four treatments had a significantly higher alfalfa yield than T0. For H2, T2 and T4 had a significantly higher alfalfa yield than T0. For H3, T1~T4 were not distinguishable from T0 in alfalfa yield. Compared to T0, T4 had significantly higher total alfalfa yield in 2022, and the increase was 6.3%.
The impacts of the fertilizers and soil conditioner were more pronounced in 2023. For H1, T1~T4 had a higher alfalfa yield than T0. For H2, T2~T4 had a higher alfalfa yield than T0, but T1 was indistinguishable from T0. For H3, T2 and T4 had a higher alfalfa yield than T0 and T1, and T4 had a higher alfalfa yield than T3. For H4, T4 had a higher alfalfa yield than T0. Compared to T0, the total alfalfa yield of 2023 increased significantly at T2, T3, and T4, by 9.1%, 10.0%, and 14.2%, respectively. In addition, T4 had a significantly higher (8.4%) alfalfa yield than T1.

3.2. Alfalfa Quality

Figure 1 shows that the crude protein was indistinguishable among treatment groups except for the following: H3 in 2022, where T0 had a significantly lower level of crude protein than T1~T4, H1 in 2023, where both T0 and T1 had significantly lower levels of crude protein than T3 and T4 (T0, 15.6%; T1,15.7%; T3, 17.3%; T4, 17.2%), and H2 in 2023, where T0 had a significantly lower level of crude protein than T3 and T4 (T0, 16.3%; T3, 17.9%; T4, 17.7%).
For both 2022 and 2023, both NDF and ADF were statistically indistinguishable among groups at each harvest (Figure 1). Within each group, H2 always had the lowest NDF and ADF (Figure 1), as well as the highest RFV (Figure 2). At H2, compared to T0 and T1, T4 had 10.4% and 5.8% higher RFVs in 2022, and 10.0% and 8.4% higher RFVs in 2023, respectively. In addition, for H4 of 2023, T4 had 12.0% higher RFVs than T0 and a 10.7% higher RFV than T1.

3.3. Soil Characteristics

Table 3 shows the properties of the soil samples collected after H4 in 2023. There was no statistically significant difference in pH across treatments or soil layers. The SS always increased with soil depth. For the surface soil (0~20 cm), T1 had 22.1%, 18.2%, and 20.5% higher SS than T0, T3, and T4, respectively. The SS dropped with the application of the soil conditioner, as T3 had 15.6% less SS than T1, and T4 had 12.4% less SS than T2.
Within each soil layer, there was no statistically significant difference in SOM among different groups, although compared to T0, T3 and T4 had 4.6% and 5.6% higher SOM in the 0~20 cm layer and 4.5% and 4.3% higher SOM in the 20~40 cm layer (Table 4). Within each group, SOM decreased with soil depth.
The AN, AP, and AK all decreased with soil depth (Table 4). For the 0~20 cm and 20~40 cm layers, T3 and T4 always had significantly higher AP than other treatments. For the 0~20 cm layer, T3 had 68.8% more AP than T1 and 120.2% more AP than T0, and T4 had 43.8% more AP than T2 and 125.6% more AP than T0. For the 20~40 cm layer, T3 had 33.3% more AP than T1 and 63.5% more AP than T0, and T4 had 41.9% more AP than T2 and 77.1% more AP than T0.
For AN, the only statistically significant difference existed between T4 and T0 in the 20~40 cm layer, where the former was 27.1% higher. For all soil layers, T1~T4 had significantly higher AK than T0, but there was no statistically significant difference among the four treatment groups themselves.

3.4. Correlation Between Alfalfa Yield and Soil Properties

Figure 3 shows that the alfalfa yield was correlated significantly positively with the SOM (p = 0.031) of the surface soil (0~20 cm layer) and the AP of all three soil layers. It was also correlated significantly positively (p = 0.012) with the AN of the 40~60 cm soil layer and highly significantly positively (p = 0.002) with the AN of the 20~40 cm soil layer. It was negatively correlated with the SS of the surface soil (0~20 cm layer), although without statistical significance (p = 0.909). The SOM was correlated strongly with the soil nutrients within and across soil layers.

4. Discussion

4.1. Effect of CRF on Alfalfa Yield

Many studies have suggested that fertilization can increase the yield of alfalfa [30,31,32]. Wang et al. [33] found that N fertilization significantly improves the alfalfa yield at the first two cuttings in the first year. Elgharably and Benes [34] suggested that, in cultivating alfalfa, N fertilization helps to alleviate salt stress and improve the biomass production of shoots. The present study had similar findings. In both 2022 and 2023, routine fertilization significantly increased the alfalfa yield of the first harvest, although it had little impact on the subsequent harvests. In contrast, CRF significantly enhanced the alfalfa yield in all but the last harvest. The CRF used in this study is water-based resin-coated urea fabricated in our lab, which, according to our previous studies, can gradually release nitrogen into the soil over 180 days [15]. Water-based resin can realize nitrogen release even when the soil has low water content because of its good hydrophilicity and water absorption ability. Thus, compared to urea, CRF has a more lasting influence, and it can still supply nutrients to the crop long after it has been applied. This sustained provision of nutrients thus improves the alfalfa yield of later harvests because nutrients are absorbed and utilized over extended periods. In this way, CRF improves both the utilization rate of nitrogen and the total (annual) yield of alfalfa. Li et al. [7] reported similar findings for saline–alkali reclamation areas at the Yellow River Delta. They found that, while quick-acting fertilizers give better alfalfa yield in the short term, CRF increases the yield by up to 22% on a yearly basis, as it promotes the branching and root development of alfalfa.

4.2. Effect of CRF with Soil Conditioner on Alfalfa Yield and Quality

The application of the soil conditioner in addition to fertilizers further improved the alfalfa yield and quality. For both 2022 and 2023, the alfalfa yield was the highest for T4 (CRF with soil conditioner) and the second highest for T3 (urea with soil conditioner). Fertilization on its own (T1~T4 vs. T0) had little impact on the nutritional quality of alfalfa, since its only influence was to significantly increase the crude protein content for H3 of 2022. However, when the soil conditioner was also applied (T3 vs. T1 and T4 vs. T2), the crude protein increased significantly in H1 and H2 of 2023. In both 2022 and 2023, T4 always had the lowest ADF and NDF and the highest RFV. Crude protein, NDF, and ADF are important indicators of the nutritional value of forage [35,36]. The livestock tends to eat less when NDF is high and has poorer digestion when ADF is high. The RFV is a comprehensive reflection of NDF and ADF, and the forage has higher nutritional value when its RFV is high [37]. Therefore, in this work, the application of the soil conditioner not only increased the yield but also improved the nutritional value of the alfalfa. The increase in alfalfa quality may be related to the improvement of the saline–alkali soil by the conditioner, as discussed below.

4.3. Amelioration of Saline–Alkali Soil with the Combined Application of CRF and Soil Conditioner

The combined use of CRF and soil conditioner improved the SOM, AN, and AP of the 0~40 cm soil and reduced the SS of the surface soil (0~20 cm). In fact, significant positive correlations existed between alfalfa yield and SOM, AN, and AP, and significant negative correlation existed between alfalfa yield and SS.
In the soil conditioner, the fermented cow dung, fermented bacterial residues, biochar, and humic acid were all excellent sources of organic materials. The organic matter content of the soil conditioner was 32.16%. The SOM improved significantly after the soil conditioner was applied for two consecutive years. The SOM is a basic parameter of soil fertility, and it significantly affects the water retention capacity, the nutrient supply capacity, and the buffering capacity of the soil [38,39]. For saline–alkali soil, a higher SOM content can improve the soil structure, reduce ground evaporation, promote salt leaching, inhibit rising salinity, and promote soil microbial activity, all of which contribute to the optimization of water, fertility, and salt [40,41]. The reduction in salinity may also be related to the characteristics of biochar in the conditioner. The surface of biochar is rich in ions like Ca2+ and Mg2+, and they can exchange the Na+ adsorbed in the soil colloid to reduce the amount of sodium salt in the soil and thus reduce SS [42,43]. In addition, the vermiculite in the soil conditioner has a porous structure and good swelling properties, and it is beneficial to water absorption, moisture retention, and air permeation [44]. It can absorb the soluble salts in the soil to reduce SS.
The increase in AN and AP can be attributed to the following reasons. First, the slow release of N by the CRF reduced the volatilization of ammonium N and the leaching loss of nitrate N [45]. Second, the addition of the soil conditioner reduced the SS and improved the quality of the saline–alkali land, thus promoting the transformation of soil nutrients (e.g., N and P) and improved their effectiveness [46]. The soil nutrients also experienced less leaching loss as they could be adsorbed better [23]. Some studies reported that the application of biochar in saline–alkali lands can effectively increase the SOM and the AP. For example, Tang et al. [47] found that, after 5% biochar was applied to saline–alkali land for 50 days, the SOM and AP increased 353.96% and 232.09%, respectively. They suggested that biochar enhances the adsorption of phosphate through electrostatic attraction, precipitation, anion exchange, etc. Third, the AN and AP increased also because the soil conditioner itself contained some nutrients. The different treatments had relatively little impact on the AK of the soil because the soil was rich in K, and all fertilization schemes applied the same level of K. For all treatment groups, during alfalfa growth, AK was always at a relatively high level.

5. Conclusions

Alfalfa was grown in the coastal saline–alkali land of the Yellow River Delta, and different land management practices were tested. While using urea as the nitrogen fertilizer only improved the yield of the first harvest in each year, using CRF (water-based resin-coated urea) as the nitrogen fertilizer improved the yield throughout the year except in the last harvest. Compared to urea, CRF provided nitrogen in a more sustained manner. Using soil conditioner together with CRF further improved the alfalfa yield and the alfalfa quality. The combined application of CRF and soil conditioner reduced the SS of the surface soil (0~20 cm) and increased the SOM, AN, and AP of the 0~40 cm soil layer. Hence, the application of soil conditioner and CRF could improve the soil properties of the coastal saline–alkali land at the Yellow River Delta and enhance alfalfa productivity. Further research is needed to develop CRF with longer release time such that the fertilizer can match the demand for nutrients throughout the growing seasons of alfalfa, elucidate the optimal application strategies of the soil conditioner, and reveal the biomolecular mechanisms relevant to the soil conditioner.

Author Contributions

Conceptualization, P.L. and Z.L.; data curation, P.L.; formal analysis, B.W.; investigation, P.L., B.W., Z.Z. and G.W.; methodology, B.W.; resources, P.L., Z.Z. and G.W.; supervision, Z.L.; validation, P.L. and Z.L.; writing—original draft, P.L.; writing—review and editing, Z.L. All authors have read and agreed to the published version of the manuscript.

Funding

This work was funded by the National Key Research and Development Program of China (2021YFD1900903), the National Natural Science Foundation of China (32272227), the Key R&D Program of Shandong Province, China (2024SFGC0405), the Earmarked Fund for CARS (CARS-34) and Agricultural Science and Technology Innovation Project of Shandong Academy of Agricultural Sciences (CXGC2025C04).

Data Availability Statement

The datasets used and/or analyzed during the current study are available from the corresponding author upon reasonable request.

Conflicts of Interest

The authors declare no conflicts of interest.

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Figure 1. The nutritional quality of alfalfa. Vertical bars represent standard deviation. Different lowercase letters above the data bars of the same color indicate statistically significant differences (p < 0.05). ADF, acid detergent fiber; NDF, neutral detergent fiber. T0, no fertilization; T1, urea with P&K fertilizers; T2, controlled-release fertilizer (CRF) with P&K fertilizers; T3, urea, P&K fertilizers, and soil conditioner; T4, CRF, P&K fertilizers, and soil conditioner. H1, the first harvest; H2, the second harvest; H3, the third harvest; and H4, the fourth harvest.
Figure 1. The nutritional quality of alfalfa. Vertical bars represent standard deviation. Different lowercase letters above the data bars of the same color indicate statistically significant differences (p < 0.05). ADF, acid detergent fiber; NDF, neutral detergent fiber. T0, no fertilization; T1, urea with P&K fertilizers; T2, controlled-release fertilizer (CRF) with P&K fertilizers; T3, urea, P&K fertilizers, and soil conditioner; T4, CRF, P&K fertilizers, and soil conditioner. H1, the first harvest; H2, the second harvest; H3, the third harvest; and H4, the fourth harvest.
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Figure 2. The relative feed value (RFV) of alfalfa. Vertical bars represent standard deviation. T0, no fertilization; T1, urea with P&K fertilizers; T2, controlled-release fertilizer (CRF) with P&K fertilizers; T3, urea, P&K fertilizers, and soil conditioner; T4, CRF, P&K fertilizers, and soil conditioner. H1, the first harvest; H2, the second harvest; H3, the third harvest; and H4, the fourth harvest.
Figure 2. The relative feed value (RFV) of alfalfa. Vertical bars represent standard deviation. T0, no fertilization; T1, urea with P&K fertilizers; T2, controlled-release fertilizer (CRF) with P&K fertilizers; T3, urea, P&K fertilizers, and soil conditioner; T4, CRF, P&K fertilizers, and soil conditioner. H1, the first harvest; H2, the second harvest; H3, the third harvest; and H4, the fourth harvest.
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Figure 3. Correlation between soil physicochemical factors and alfalfa yield. The numbers at the end of the labels denote the soil layer as follows: 1, 0~20 cm soil layer; 2, 20~40 cm soil layer; 3, 40~60 cm soil layer. AY, alfalfa yield; SS, soil salinity; SOM, soil organic matter; AN, available nitrogen; AP, available phosphorous; and AK, available potassium.
Figure 3. Correlation between soil physicochemical factors and alfalfa yield. The numbers at the end of the labels denote the soil layer as follows: 1, 0~20 cm soil layer; 2, 20~40 cm soil layer; 3, 40~60 cm soil layer. AY, alfalfa yield; SS, soil salinity; SOM, soil organic matter; AN, available nitrogen; AP, available phosphorous; and AK, available potassium.
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Table 1. Basic physical and chemical properties of the soil before the experiment.
Table 1. Basic physical and chemical properties of the soil before the experiment.
Soil LayerpHBulk Density
(g cm−3)		SOM †
(g kg−1)		Salinity
(g kg−1)		EC †
(µS cm−1)		Available N
(mg kg−1)		Available P
(mg kg−1)		Available K
(mg kg−1)
0~20 cm9.191.2910.461.5231249.6410.24132.67
20~40 cm9.171.327.722.6390735.188.02106.67
† SOM, soil organic matter; EC, soil electrical conductivity.
Table 2. Effects of fertilizer and soil conditioner treatment on alfalfa yield.
Table 2. Effects of fertilizer and soil conditioner treatment on alfalfa yield.
YearTreatmentT0 §T1 §T2 §T3 §T4 §
2022H1 †4020 ± 90.8 b4294 ± 103.9 a4269 ± 89.7 a4308 ± 98.2 a4284 ± 86.7 a
H2 †2742 ± 95.2 b2826 ± 99.2 ab2903 ± 85.1 a2853 ± 80.9 ab2922 ± 82.3 a
H3 †2126 ± 103.5 a2145 ± 98.4 a2163 ± 92.8 a2225 ± 96.8 a2242 ± 87.2 a
Total8889 ± 280.6 b9265 ± 289.8 ab9335 ± 253.9 ab9386 ± 273.3 ab9448 ± 247.9 a
2023H1 †3625 ± 131.5 b3977 ± 160.1 a3917 ± 126.5 a4110 ± 162.6 a4079 ± 160.1 a
H2 †3242 ± 158.1 b3484 ± 194.2 ab3599 ± 95.6 a3650 ± 217.8 a3776 ± 146.7 a
H3 †3325 ± 109.0 c3343 ± 55.3 c3635 ± 141.5 ab3481 ± 66.8 bc3794 ± 89.9 a
H4 †2134 ± 177.3 b2188 ± 102.0 ab2296 ± 175.5 ab2313 ± 116.3 ab2445 ± 73.4 a
Total12,326 ± 556.0 c12,992 ± 483.2 bc13,447 ± 533.8 ab13,553 ± 533.6 ab14,077 ± 421.3 a
§ Values are expressed as mean ± SD (Unit: kg ha−1). Different lowercase letters in the same row indicate significant differences (p < 0.05) among treatments. T0, no fertilization; T1, urea with P&K fertilizers; T2, controlled-release fertilizer (CRF) with P&K fertilizers; T3, urea, P&K fertilizers, and soil conditioner; T4, CRF, P&K fertilizers, and soil conditioner. † H1, the first harvest; H2, the second harvest; H3, the third harvest; and H4, the fourth harvest.
Table 3. Soil pH and salinity after treatment for two years.
Table 3. Soil pH and salinity after treatment for two years.
Soil LayerT0 §T1 §T2 §T3 §T4 §
pH0~20 cm8.49 ± 0.22 a8.76 ± 0.18 a8.64 ± 0.07 a8.67 ± 0.09 a8.72 ± 0.13 a
20~40 cm8.94 ± 0.21 a8.84 ± 0.10 a8.87 ± 0.17 a8.71 ± 0.28 a8.88 ± 0.15 a
40~60 cm9.01 ± 0.22 a8.77 ± 0.17 a8.88 ± 0.19 a9.02 ± 0.07 a8.76 ± 0.20 a
Salinity
(g kg−1)		0~20 cm1.54 ± 0.11 b1.88 ± 0.17 a1.78 ± 0.16 ab1.59 ± 0.10 b1.56 ± 0.18 b
20~40 cm1.91 ± 0.15 a2.13 ± 0.20 a2.05 ± 0.21 a2.03 ± 0.30 a1.95 ± 0.24 a
40~60 cm2.27 ± 0.33 a2.49 ± 0.19 a2.40 ± 0.16 a2.34 ± 0.31 a2.29 ± 0.25 a
§ Values are expressed as mean ± SD. Different lowercase letters in the same row indicate significant differences (p < 0.05) among treatments. T0, no fertilization; T1, urea with P&K fertilizers; T2, controlled-release fertilizer (CRF) with P&K fertilizers; T3, urea, P&K fertilizers, and soil conditioner; and T4, CRF, P&K fertilizers, and soil conditioner.
Table 4. Soil organic matter and nutrient contents after treatment for two years.
Table 4. Soil organic matter and nutrient contents after treatment for two years.
Soil LayerT0 §T1 §T2 §T3 §T4 §
SOM
(g kg−1)		0~20 cm9.12 ± 0.23 a9.20 ± 0.36 a9.29 ± 0.33 a9.54 ± 0.28 a9.63 ± 0.34 a
20~40 cm6.18 ± 0.51 a6.44 ± 0.31 a6.39 ± 0.05 a6.46 ± 0.23 a6.45 ± 0.35 a
40~60 cm3.74 ± 0.58 a3.73 ± 0.47 a3.77 ± 0.45 a3.79 ± 0.42 a3.80 ± 0.49 a
Available N
(mg kg−1)		0~20 cm59.64 ± 1.50 a58.42 ± 3.54 a60.06 ± 3.70 a65.18 ± 7.84 a67.62 ± 5.27 a
20~40 cm38.76 ± 2.13 b43.64 ± 5.79 ab46.83 ± 4.79 ab47.77 ± 5.02 ab49.27 ± 5.54 a
40~60 cm25.81 ± 3.94 a26.13 ± 4.17 a26.69 ± 4.05 a27.11 ± 4.32 a27.22 ± 2.56 a
Available P
(mg kg−1)		0~20 cm3.32 ± 1.14 b4.33 ± 0.80 b5.21 ± 1.30 ab7.31 ± 1.31 a7.49 ± 1.41 a
20~40 cm3.23 ± 0.65 b3.96 ± 0.26 b4.03 ± 0.30 b5.28 ± 0.39 a5.72 ± 0.85 a
40~60 cm3.07 ± 0.66 a3.76 ± 0.56 a3.87 ± 0.59 a3.95 ± 0.89 a4.00 ± 0.89 a
Available K
(mg kg−1)		0~20 cm92.67 ± 8.74 b124.67 ± 5.51 a120.67 ± 12.01 a118.67 ± 10.26 a128.33 ± 7.51 a
20~40 cm63.67 ± 5.13 b94.00 ± 12.49 a89.33 ± 10.44 a87.00 ± 7.23 a96.00 ± 5.29 a
40~60 cm39.00 ± 5.00 b60.67 ± 5.13 a58.67 ± 2.08 a56.67 ± 7.37 a62.00 ± 8.72 a
§ Values are expressed as mean ± SD. Different lowercase letters in the same row indicate significant differences (p < 0.05) among treatments. T0, no fertilization; T1, urea with P&K fertilizers; T2, controlled-release fertilizer (CRF) with P&K fertilizers; T3, urea, P&K fertilizers, and soil conditioner; and T4, CRF, P&K fertilizers, and soil conditioner.
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Liu, P.; Wu, B.; Zhao, Z.; Wang, G.; Liu, Z. The Application of Slow-Release Nitrogen Combined with Soil Conditioner Under the Impact of Alkaline Salinity in Alfalfa Cultivation and Soil Improvement. Agronomy 2025, 15, 923. https://doi.org/10.3390/agronomy15040923

AMA Style

Liu P, Wu B, Zhao Z, Wang G, Liu Z. The Application of Slow-Release Nitrogen Combined with Soil Conditioner Under the Impact of Alkaline Salinity in Alfalfa Cultivation and Soil Improvement. Agronomy. 2025; 15(4):923. https://doi.org/10.3390/agronomy15040923

Chicago/Turabian Style

Liu, Ping, Bo Wu, Zichao Zhao, Guoliang Wang, and Zhaohui Liu. 2025. "The Application of Slow-Release Nitrogen Combined with Soil Conditioner Under the Impact of Alkaline Salinity in Alfalfa Cultivation and Soil Improvement" Agronomy 15, no. 4: 923. https://doi.org/10.3390/agronomy15040923

APA Style

Liu, P., Wu, B., Zhao, Z., Wang, G., & Liu, Z. (2025). The Application of Slow-Release Nitrogen Combined with Soil Conditioner Under the Impact of Alkaline Salinity in Alfalfa Cultivation and Soil Improvement. Agronomy, 15(4), 923. https://doi.org/10.3390/agronomy15040923

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