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Article

Residual Effects of Pig Slurry Fertilization in a Mediterranean Rainfed Cereal System

by
Carlos Ortiz
1,2,
Jaime Boixadera
2 and
Àngela D. Bosch-Serra
2,*
1
Department of Agriculture, Livestock, Fisheries and Food, Generalitat de Catalunya, Av. Alcalde Rovira Roure 191, E-25198 Lleida, Spain
2
Department of Chemistry, Physics, Environmental and Soil Sciences, University of Lleida, Av. Alcalde Rovira Roure 191, E-25198 Lleida, Spain
*
Author to whom correspondence should be addressed.
Agronomy 2024, 14(11), 2552; https://doi.org/10.3390/agronomy14112552
Submission received: 30 September 2024 / Revised: 21 October 2024 / Accepted: 27 October 2024 / Published: 30 October 2024
(This article belongs to the Section Soil and Plant Nutrition)
Browse Figures
Versions Notes

Abstract

:
An increase in nitrogen (N) use efficiency (NUE) in agriculture is a requirement for sustainable development. The reduction in nitrogen inputs might benefit from the residual N of former organic fertilization procedures. A 10 year experiment was established in a rainfed Mediterranean system (barley–wheat rotation). The objective of this experiment was to quantify the N residual effects of a single pig slurry (PS) application at sowing (20, 40, and 80 m3 ha−1) and up to three years later. The mineral N equivalence method was used to compare the grain yield (GY) and the whole-plant N uptake (WPNU) between the slurry fertilized plots (slurries applied in previous years) and annual mineral N fertilized ones (30, 60, 90, 120, and 150 kg N ha−1). From the total N applied with PS, a fraction of, ca., 21% accounted for the residual equivalent mineral N for a total period of three years after the PS application. For the 20 m3 ha−1 rate, the relative residual N based on the GY and WPNU equaled to 89–90% of the applied organic N, respectively. This rate also allowed for an increase in NUE values to above 33%. In semiarid areas, the introduction of residual N when scheduling fertilization is important to reduce N inputs and to increase NUE.

1. Introduction

Nitrogen (N) is a major nutrient in agricultural production, and its sustainable management is a matter of concern. Sustainable management includes the implementation of a circular N economy and the increase in N use efficiency (NUE) as measures to control reactive N losses out of agricultural systems [1]. In 2013, some authors [2] stated that an increase of 50% in the global average NUE, in terms of output/input [3], would reduce the total N input requirement to 108 Tg N year−1. In the case of Europe, the same authors considered that a reduction in N fertilization would be possible, as its average current NUE value for crop/vegetal consumption is 33%. Moreover, the EU Nitrogen Expert Panel considers the range of desired NUE values to be between 50% and 90% [3].
Some European governments are implementing the Farm-to-Fork Strategy [4], which addresses the use of fertilizers and sets forth an ambitious plan to diminish their use by at least 20%. This challenge reinforces the need for an NUE increase, mainly regarding N of organic origin. Organic wastes and their permanence in the economy as a resource are also key aspects of a circular economy [5].
The availability of organic fertilizers from rearing activities is very significant in some European areas. For instance, Spain is the primary pig-producer country of the 27 EU countries at 29.2 million heads, which represents one fifth of the European pig population [6]. Half of this production is concentrated in two Northeastern Spanish regions, Catalonia and Aragon, where slurries are mainly used as fertilizers in cereal crops. Furthermore, these regions hold all of their animal dejection pressure in 14.5% of Spanish cultivated land [7].
Organic fertilizers contain mineral N (mainly ammonium ions), and organic N forms (complex molecules) in different proportions, from 30 to 75% [8]. Mineral fertilizers only contain N in mineral forms. Therefore, the fate of N from mineral fertilizers can be easily predicted using models [9]. However, the evolution of organic N in soil is more difficult to predict due to the different processes controlling N transformations and the quality of the associated organic C [10]. Nitrogen availability to plants from the applied N in the form of organic fertilizers can last different cropping seasons due to the mineralization of the applied organic N [11]. In manure, the composition ratios of organic carbon vs. total N, and ammonium-N (NH4+-N) vs. the organic N ratio, are considered indicators of N availability to plants [12]. Nevertheless, in pig slurries, a significant proportion of NH4+-N is shortly immobilized after application, as it is retained as organic N [13]. This process can mask the potential contribution of slurry applications to the mineral N soil pool in the following cropping seasons. This available mineral N from previous slurry fertilization might be important in rainfed Mediterranean semiarid environments, where water drainage is constrained by low precipitation [14] and, consequently, nitrate leaching. This N contribution (postponed over time) might be important in order to adjust (and reduce) annual N fertilization. Several approaches have been used to estimate its value in manure. The concept of decay series was developed by [11]. It is a method that indicates the amount of available mineral N for the cropping seasons following manure application. However, some authors [15] consider that the decay series underestimate the mineral N fertilizer equivalence values, especially in dryland areas. The recovery method [16], the fertilizer equivalence method [17], and the use of labelled 15-N in manure [18,19] have also been used to describe how N is released over time and its potential availability to plants.
In semiarid environments, despite the potential importance of N availability from PS in the years following its application, there is a lack of information about it under this context. Most authors have worked under Central and Northern European conditions [20] or with irrigation systems [15,16]. Also, many field experiments about residual effects have been performed in manured fields, which make it impossible to observe the consequences of single applications [16]. Additionally, mid-/long-term experiments are needed to estimate the release of N beyond the year of the PS application.
In this context, a mid-term fertilization experiment using pig slurries and lasting for a period of ten years was set up in a field where mineral fertilization had been implemented as the only source of N many years ago. Our hypothesis was that the remineralization of the immobilized organic N from slurry ammonium N, along with the mineralization of the organic N applied with slurries, might release a non-negligible amount of mineral N the following years (up to three) after the slurry application. The N release should positively affect yields and plant N uptake (residual effect). The quantified residual effect might help increase the NUE in these systems.
The objectives of this experiment were (a) to assess the cumulative and residual effects of PS fertilization strategies on yields and whole-plant N uptakes based on equivalent mineral N fertilizer values and (b) to obtain a global NUE.

2. Materials and Methods

The experiment was conducted over a period of ten years, from October 2000 to June 2010, in a semiarid Mediterranean rainfed area, located in Oliola (NE of Spain, 41°52′31″ N, 1°9′8″ E, with an altitude of 440 m a.s.l.).
The annual rainfall (for each cropping season) in the 10 year experimental period ranged from 328 to 565 mm (Figure 1), and 73% of it occurred during the winter cereal growing season (October–June).
The soil is classified as Typic Xerofluvent [21]. At the beginning of the experiment, the upper soil layer (from zero to 0.3 m in depth) had a silty loam texture and a soil pH of 8.2 (1:2.5, soil:distilled water), with a calcium carbonate equivalent content of 300 g kg−1. The soil water retention (from zero to 0.3 m in depth) at −33 kPa was 0.27 cm3 cm−3, and at −1500 kPa, it was 0.17 cm3 cm−3. The electrical conductivity (1:5, soil:distilled water) was below 0.2 dS m−1 at 25 °C, the organic matter content [22] was 15 g kg−1, the available Olsen phosphorus [23] was 17 mg kg−1, and the ammonium acetate extractable potassium (1 mol L−1 and pH = 7) was 76 mg kg−1. Potential soil rooting was higher than 1 m in depth. The initial soil mineral N content (October 2000) was 41 kg of NO3−-N ha−1 from 0 to 0.3 m in depth and 72 kg of NO3−-N ha−1 from 0 to 0.90 m in depth.

2.1. Experimental Design and Agronomic Management

It was ensured that no manure had been applied for a long period of time before the establishment of the trial. Annual crops were sown under rainfed conditions following a typical winter cereal rotation of barley (Hordeum vulgare L.) and wheat (Triticum aestivum L.) plus a one-year fallow period (2007/08). Wheat was sown in the 2002/03, 2005/06, and 2008/09 cropping seasons. Fallow was introduced because of a regulation of the European Common Agricultural Policy, lasting from 1992 to 2008. Winter cereals were sown in early November and harvested at the end of June (Table 1). Cereal straws were annually removed from the field, and the stubble was buried by tillage.
The experiment included a randomized complete block design with nine treatments that were replicated three times. The treatments (Table 2) included three PS doses, four mineral N (MN) doses, and a control (with no N applied). The PS treatments were applied at sowing 20, 40, or 80 m3 ha−1 every four years to account for the residual effects (Table 2). The doses applied always followed geometric progression, with a common ratio of 2. The MN treatments were applied annually at the doses of 30, 60, 90, and 150 kg of N ha−1 at sowing and at cereal tillering, split as follows: 0–30, 30–30, 30–60, and 30–120 kg of N ha−1 (sowing–tillering). Ammonium nitrate (33.5% N) was used as a fertilizer. In the initial three cropping seasons (from 2000–2001 to 2003–2004), the annual doses of PSs were complemented with 60 kg of N ha−1 year−1 as ammonium nitrate (33.5% N) at cereal tillering, according to traditional management practices, but this topdressing fertilization was not included in the following seasons. Experimental mineral fertilizer plots and the control were 12 m long and 7 m wide, and the rest of plots were 20 m long and 12 m wide.
Pig slurry was spread using a conventional splash-plate system, while MN was applied by hand. Both were incorporated into the soil by disc harrowing within 24 h after spreading. The control (no N applied) and MN treatments received 42 kg of P and 89 kg of K ha−1 year−1 at sowing. The total N content of the PS averaged 7.7 g of N kg−1, ranging from 4.7 to 8.9 g of N kg−1 (Table 3). The ratio of NH4+-N/the total N averaged 71%. The averages of the total N applied with slurries in the studied period (eight applications) were 171, 309 and 589 kg of N ha−1 for the slurry rates of 20, 40, and 80 m3 ha−1, respectively. If the 2008/09 season is excluded (application after fallowing), the averages of the total N applied were 181, 327 and 613 kg of N ha−1 for the slurry rates of 20, 40, and 80 m3 ha−1, respectively.
Slurries were annually sampled from each tank and analyzed to quantify the actual amount of N applied [24]. The organic N was obtained as a difference between the total and ammonium N (Table 3). A total amount of 24 slurry samples were analyzed during the 10 year trial.
The grain yield (GY) of each plot was obtained annually with a cereal micro-plot harvester that was 1.5 m wide. The grain yield was adjusted to dry content. The whole-plant biomass was measured by drying at 60 °C. The nitrogen in the grain and in the rest of the plant (WPNU) were determined by the Kjeldahl method [25]. From the grain and plant biomass and their N content, the whole-plant N uptake (WPNU) was quantified.
The grain yield and WPNU response curves were obtained each year for the mineral N.

2.2. Estimation of Mineral N Fertilizer Equivalence in Years Following Slurry Application

The mineral N fertilizer equivalence (MNFE) was calculated in the years following the pig slurry application (for up to three years). Two crop parameters were used: GY and WPNU. For each crop parameter, data from previous slurry fertilized plots were entered into the mineral regression curves, and the fertilizer mineral rate that would have produced the same GY or WPNU values (the MNFE) was determined [26,27]. Mineral N fertilizer equivalents for replications of a given previous slurry treatment were averaged.

2.3. Estimation of Residual Effects

The residual effects in subsequent cropping seasons after the pig slurry application were determined from the GY and the WPNU data and were based on the MNFE method [28]. The relative first-year residual effects (RE1) were measured on non-fertilized plots in the 2002, 2003, 2004, 2006, 2007, and 2010 harvests; the relative second-year residual effects (RE2) in the 2003, 2004, 2005, 2007, and 2009 harvests; and the relative third-year residual effects (RE3) in the 2004, 2005, 2006, 2009, and 2010 harvests (Table 2).
The relative residual effect for a specific fertilization was calculated by dividing the MNFE in each of the three following years after the PS application by the initial total applied N (year of slurry application, year0) and is expressed as a percentage. It was also calculated as the quotient of the MNFE and the initial total amount of organic N applied (year of slurry application, year0).
Thus, RE1 was calculated as the MNFE in year0+1 divided by the total N applied in year0. RE2 was calculated as the MNFE in year0+2 divided by the total N applied in year0. RE3 was calculated as the MNFE in year0+3 divided by the total N applied in year0.

2.4. Nitrogen Use Efficiency

The nitrogen use efficiency (NUE) was estimated for each treatment and year of fertilizer application following the proposal of [3], therefore, according to Equation (1).
NUE = N uptake (kg ha−1)/N applied (kg ha−1)
Nitrogen uptake refers to the WPNU, and N applied refers to the total N applied as a fertilizer.
A progressive and global NUE for N fertilization was calculated including the WPNU in the years following application. In this case, N uptake refers to the WPNU at the year of application (year0) plus the WPNU in the years following initial fertilizer application: first year (year0+1), first plus second year (year0+1+2), and first plus second plus third year (year0+1+2+3). Nitrogen applied always refers to the initial fertilizer application (from which the residual effects are quantified).

2.5. Statistical Analysis

The package SAS v9.4 [29] was used for a statistical analysis. The grain yield and WPNU response curves to mineral N were obtained by applying the polynomial regression model. Data from years without significant differences on yields between mineral fertilization treatments (including the control) were rejected. This decision was supported by a previous analysis of variance using the general lineal model (GLM) procedure.

3. Results

3.1. Grain Yield and Whole-Plant Nitrogen Uptake

In most of the observed years, the GY and WPNU responded positively to the MN annual applications (Table 4). The coefficient of determination (R2) ranged from 0.58 to 0.90 for GY and from 0.51 to 0.91 for WPNU. The grain yield data of 2002/03, 2004/05, 2005/06, and 2008/09 were not used for further MNFE calculations, as no significant differences were found between MN treatments, according to a previous analysis of variance.
Grain yields for specific annual fertilizations with slurries averaged 3.6 Mg ha−1, but they showed a year variability from 1.6 to 5.5 Mg ha−1 (Figure 2). The maximum attained grain yields from 2000/01 to 2009/10 (excluding the fallow season of 2007/08) were 4.4, 4.8, 2.9, 3.8, 1.9, 3.1, 3.0, 6.1, and 7.0 Mg ha−1, respectively. The maximum WPNU, for the same period, was 154, 143, 163, 127, 84, 189, 181, 440, and 259 kg of N ha−1 (Figure 3). Grain yields from the 2002/03, 2004/05, and 2005/06 cropping seasons were not considered in the NUE and further NFRV calculations because of the reduced response of the crop to the added N (Table 4). However, for the WPNU, the data from all cropping seasons were used in further analyses. After the fallow period of 2008/09, no effect of N fertilization was observed on the GY and WPNU.

3.2. Mineral N Fertilizer Equivalence in Years Following Slurry Application

The MNFE values tended to be higher as the rates increased, and they diminished with time (Table 5). This pattern was observed when the results referred to both the GY and WPNU and for the first and second year after the PS application. No clear trend was observed in the third year after fertilization. Moreover, the MNFE varied over the years.
Based on the GY values (Table 5), the MNFE for the first year after the PS application of 80 m3 ha−1 was around 121 kg of N ha−1 in 2001/02, while it was only 55, 69, and 32 in the 2003/04, 2006/07, and 2009/10 cropping seasons, respectively (Table 5). The maximum MNFE value for the second residual year was 40 kg ha−1 in 2006/07 (for 80 m3 ha−1), which doubled the figure obtained in 2003/04. The third-year values of 19 and 35 kg of N ha−1 were obtained in 2003/04 and 2009/10, respectively.
Based on WPNU (Table 5), the MNFE values followed a similar pattern to those of the GY ones, although the figures are slightly lower (Table 5). In the first year, and for the 20, 40, and 80 m3 ha−1 rates, the average MNFE was 14, 29, and 87 kg N ha−1. For the second year after the PS application, and for the same rates, the MNFE average values were 11, 17, and 26 kg of N ha−1, respectively. For the third year, they were 11, 11, and 27 kg of N ha−1, respectively.

3.3. Residual Effects

Residual N effects lasted three years after application, decreasing with time (Table 6). Important variations of the RE values were observed between the cropping seasons related to the previously described variations in the MNFE (Table 5).
Based on the GY values, the RE1 average over the total N (9–10%) or over the organic N (34–39%) was similar between the slurry rates (Table 6). Over the total N, when accounting for RE2, the lowest rate (20 m3 ha–1) attained a 10% value, which was 30% and 60% higher than for the rates of 40 and 80 m3 ha–1, respectively. For RE3, as the obtained values over the total N were low (from 2 to 4%), it was difficult to observe a trend related to slurry rates. If numbers were based on the WPNU or were expressed over organic matter, the figures associated with different rates showed higher variability. However, three years after the slurry application, the recovered N ranged from 18 to 23% of the total N applied and from 65 to 90% of the organic N applied (Figure 4). The lower rate of 20 m3 ha–1 recovered the highest percentage of N, irrespective of the way it was quantified, either over the GY or over the WPNU. However, there is no clear trend of residual effect reduction with increasing application rates (Figure 4).

3.4. Nitrogen Use Efficiencies

The nitrogen use efficiency decreased as the slurry rate increased. It also increased if the residual effect was included (Table 7). Globally, if the cropping season after fallowing (2008/09) was not included, the average NUE (±standard deviation) from the PS application ranged from 0.17 (±0.05) for 80 m3 ha−1 to 0.40 (±0.14) for 20 m3 ha−1. It increased from 0.24 (for 80 m3 ha−1) to 0.61 for 20 m3 ha−1 if the cropping season after fallowing was included (Table 7).

4. Discussion

The NH4+-N composition and the NH4+-N/total N ratio of the PS used in this experiment (Table 3) were included within the range of values found in farms from the northeastern part of Spain [30]. They also match the European Union’s average reported by Menzi [31]. This is a guarantee of the representativeness of their composition.
The grain yields from the 2002/03, 2004/05, and 2005/06 cropping seasons (Figure 2) were constrained by the lack of rainfall during the stem-elongation period of March and April, when the precipitation values amounted to 45, 44, and 26 mm, respectively, which is lower than the average for the area (Figure 1). These seasons can be considered spring-dry (with <70 mm of rainfall). Consequently, maximum yields of 2.5, 1.7, and 3.1 Mg ha–1 were recorded, respectively, for each cropping season. As the carbon storage is reduced in the stems, due to the reduction in carbon assimilation by water stress, less reserves might be remobilized during the grain-filling period, according to Blum [32]. Thus, no fertilization answer was obtained during these seasons, which were, therefore, not included in the RE calculations. This yield constraint linked to spring water availability has already been described in rainfed areas under similar conditions [33].
The average grain yield in this experiment was around 3.5 Mg ha–1, which is lower than in other experiments in temperate areas of Northern Europe, where the RE of slurries has been investigated [19,34]. Despite the low yields and the derived low nutrient uptakes, the results indicate a positive N effect on the GY and WPNU, and polynomial regression models were performed based on mineral N rates (Table 4). The optimal mineral N doses to maximize yields ranged from 79 to 106 kg of N ha−1, although the maximum WPNU value was obtained with higher N fertilizer rates (from 92 to 136 kg of N ha−1). Differences in N requirements can be explained by the development of a vegetative biomass that develops early in the season, which takes advantage of water availability in the winter. However, when rainfall is reduced or absent later in the season, a high biomass may cause water depletion and a lack of water available to the plant during grain filling, leading to a yield reduction [35,36].
In non-fertilized cropping seasons, the MNFE tended to be higher and increased by as much as the previously applied PS rates did (Table 5, Figure 2), as was observed by [24]. This observation reinforces the stated idea about soil N leaching constraints in these systems. However, water and nitrate leaching exist in this area [11,35], as can also be seen from the 2003/04 figures depicting the WPNU (Table 5), which are related to rainfall events (Figure 1 and Figure 3). In these systems, the data also stress the need to adjust fertilization to plant requirements, although this is difficult due to erratic rainfall events (Figure 1). The introduction of catch crops to take advantage of the potential available N at the end of the cropping season is not an option, as it has been argued that water availability is a major limitation for profitable yields.
The relative RE, for the three years following the PS application, in terms of the total MNFE over the total applied N, achieved values of 21%, no matter whether the GY or WPNU was used for such calculations (Table 6 and Figure 4). A few authors have studied the relative RE for a period longer than two years, and their obtained RE figures were lower than those obtained in our research. In fact, [16] obtained accumulated values of 7 to 16% for untreated cattle slurries in a 3 year experiment, and [17] obtained 11–12% in a 4 year experiment. The explanation of our higher relative RE values may be a consequence of the semiarid conditions of our study area, which caused the N to remain in the soil as a result of limited N leaching [11] and the additional burst of nitrification observed after drought periods, during rewetting [9]. Therefore, our results emphasize [17]’s claim that residual N should be determined for specific regional conditions.
The RE1 of 10% (Table 6) matches the 9% and 12% values reported by [28,37], who used the fertilizer equivalence method when applying PS and dairy manure, respectively. A value of 17% was obtained by [37] and the values of 7% and 2.7% by [17,18], respectively. Differences in RE1 between authors can also be explained by the composition of manure, which influences N dynamics. As PS and digested slurries contain more NH4+-N than dairy manure, a lower RE1 value should be expected, as suggested by [16]. Furthermore, RE2 values were also higher than figures found in the literature: 2% [17], 2.3%, [38], and 3% [28]. In addition, RE3 was still noticeable in our experiment, with values of 3% and 5%, based on the GY and WPNU, respectively. Such results are comparable with the ones obtained by [16,17], who obtained RE3 values of 1–4% and 2%, respectively.
When the residual N was expressed with respect to the organic N, it attained values of around 89–90% for GY and WPNU, respectively (20 m3 ha−1 PS rate, Figure 4). Such high values do not fully match those in the current literature. Some authors [13] recovered 3 to 16% of the applied organic N one year after its application, and [17] achieved only 1–16% of the organic N fraction in a 4 year residual period. These important differences may be explained by the Mediterranean conditions of the area in which the present experiment was set up. Therefore, mineral N, which constitutes a higher proportion of the N in PS, may remain in soil for longer than one growing season, as suggested by [39], facilitating immobilization and further remineralization processes. As leaching in these soils occurs only in random years [14], high soil nitrate contents might be also available at sowing from previous single and repeated PS applications [9].
The residual N from PS applications in limited rainfall scenarios must be considered in fertilization schedules. The residual N from the annual recommended rates in the area at the sowing time (ca., 20 m3 ha−1) resulted in ~40 kg of N ha−1 after a 3 year period. This figure coincides with the value of N mineral content, in the upper soil layer, that the extension services in Catalonia recommend for winter cereals at sowing to assure correct plant development until subsequent topdressing [40].
The nitrogen use efficiencies when only the year of slurry application was considered was higher than the EU average (33% [3]) at the two lowest rates of 20 and 40 m3 ha−1 (Table 7). However, for only the lowest rate, NUE attained (in three cropping seasons out of the eight) the desired values higher than 50% and below 90% (Table 7). As a consequence, it might be possible to conclude that these systems are highly inefficient and threaten to contribute to N pollution. Nevertheless, if the N uptake included the WPNU of the year of application and the following one, the lowest rate consistently achieved NUE values higher than 50%. Higher rates can also attain desired NUE values, but it is necessary to add the WPNU data from the second year and/or the third year after slurry application. In this scenario, the N mineralized from organic matter was indirectly included in NUE calculations, but our results on MNFE and RE reinforced the idea that in pig slurry, NUE calculations cannot be constrained to the year of application. In fact, N availability from slurries were delayed over time, as the MNFE and RE values show (Table 5 and Table 6 and Figure 4).
In addition, high NUE values (>100%) after fallowing (the 2008/09 cropping season) not only directly highlighted potential soil mining but also the accumulation of N from organic N mineralization during the fallow period, which should be taken into account in fertilization planning to save N inputs and to increase the global NUE.
The increase in NUE required by the objectives of sustainable development [2] is feasible when pig slurries are used. It also stresses the fallow period as a source of available N for following seasons [9]. The obtained NUE values also matched the desirable NUE figures (between 50 and 90%) outlined by the European Union Nitrogen Expert Panel [3].
Hence, it is necessary to account for the available N that remains in the soil from previous applications and to incorporate other strategies such as biennial applications [41] to avoid overfertilization (mainly after a drought period), minimizing potential nitrate underground water pollution if an erratic heavy rainfall occurs, further maintaining a high global NUE. Additional management measures can be included such as splitting N applications in the springtime using trail hoses to reduce NH3 emissions [42]. Accounting for this residual available N is also important, because excessive N applications might reduce water-use efficiency [43], which is also a key management parameter in semiarid environments.

5. Conclusions

The obtained residual N figures showed variability between years, which is mainly due to annual rainfall variability. For the three rates (20, 40 and 80 m3 ha−1), the highest values were attained during the first year after the slurry application, with an average of, ca., 10–11% of the total applied N, or 36–41% of the applied organic N, based on the GY and WPNU, respectively. They decreased during the following second and third years. The accounted relative residual N, during a period of three years, averaged 21% of the total applied N, whether it was calculated on the basis of the GY or on the WPNU. The latter also accounts for, on average, 77% of the applied organic N.
In semiarid regions, the residual N from previous slurry applications lasts for three years. This should be considered in fertilization schedules in order to adjust N rates and, consequently, in order to increase its efficiency (output/input) value to above 33%.

Author Contributions

Conceptualization, À.D.B.-S. and J.B.; field experiments, À.D.B.-S. and C.O.; formal analysis, C.O.; data curation, À.D.B.-S. and C.O.; original draft preparation, C.O.; writing and editing, À.D.B.-S. and C.O.; supervision, J.B. All authors have read and agreed to the published version of the manuscript.

Funding

This work was supported by the Spanish National Institute for Agricultural Research and Experimentation (MINECO-INIA) through the projects REN01-1590, RTA04-114, RTA2010-126, RTA2013-57-C5-5, and RTA2017-88-C3-3.

Data Availability Statement

Data are available from the corresponding author upon reasonable request.

Acknowledgments

The authors acknowledge the help of E. Carrillo, G. Estudillos, J.C. Grajeda, N. Iglesias, S. Lucha, P. Medina, A. Rovira, J. Torres, and especially that provided by D. Navarro. The authors are grateful to J.M. Pijuan and J.C. Melo for their field assistance and to C. Herrero and M. Antúnez for laboratory assistance. They also thank M.M. Boixadera-Bosch for her edition support. The field maintenance from the Catalan Ministry of Agriculture, Livestock, Fisheries and Food (Generalitat de Catalunya, Catalonia, Spain) is fully acknowledged.

Conflicts of Interest

The authors declare no conflicts of interest.

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Figure 1. Total precipitation from October to September (numbers at the top of each column) and rainfall recorded during the cereal stem elongation period from March to April (numbers below the dashed line) for the 2000/01 to 2009/10 cropping seasons. The dashed line corresponds to the average historical precipitation data for March and April. Data were obtained from an automatic meteorological station located at the study site.
Figure 1. Total precipitation from October to September (numbers at the top of each column) and rainfall recorded during the cereal stem elongation period from March to April (numbers below the dashed line) for the 2000/01 to 2009/10 cropping seasons. The dashed line corresponds to the average historical precipitation data for March and April. Data were obtained from an automatic meteorological station located at the study site.
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Figure 2. Accumulated grain yield for the different pig slurry rates (20, 40, and 80 m3 ha−1) and for the cropping seasons of 2000/01 to 2009/10. The PS abbreviation indicates the year when the pig slurry was applied. No N fertilization was applied in the 2003/04 cropping season. No yield data were available for the 2007/08 cropping season, as the field was maintained under fallow conditions.
Figure 2. Accumulated grain yield for the different pig slurry rates (20, 40, and 80 m3 ha−1) and for the cropping seasons of 2000/01 to 2009/10. The PS abbreviation indicates the year when the pig slurry was applied. No N fertilization was applied in the 2003/04 cropping season. No yield data were available for the 2007/08 cropping season, as the field was maintained under fallow conditions.
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Figure 3. Accumulated whole-plant N uptake (WPNU) for the different pig slurry rates (20, 40, and 80 m3 ha−1) and for the cropping seasons of 2000/01 to 2009/10. The PS abbreviation indicates the year when the pig slurry was applied. No N fertilization was applied in the 2003/04 cropping season. No yield data were available for the 2007/08 cropping season, as the field was maintained under fallow conditions.
Figure 3. Accumulated whole-plant N uptake (WPNU) for the different pig slurry rates (20, 40, and 80 m3 ha−1) and for the cropping seasons of 2000/01 to 2009/10. The PS abbreviation indicates the year when the pig slurry was applied. No N fertilization was applied in the 2003/04 cropping season. No yield data were available for the 2007/08 cropping season, as the field was maintained under fallow conditions.
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Figure 4. Specific pig slurry rates applied (20, 40, and 80 m3 ha−1) and the associated average (n = 7) of the total N (a) or organic N (b) applied (both in dark green color). Recovered residual N in terms of grain yields (first three columns of the figure) or in terms of whole-plant N uptake (last three columns of the figure) for a period of three years after a single pig slurry (PS) application is shown in the light-green columns. The numbers in the white boxes show the relative total N residual effect over the total (a) or the organic (b) N applied and are expressed as a percentage.
Figure 4. Specific pig slurry rates applied (20, 40, and 80 m3 ha−1) and the associated average (n = 7) of the total N (a) or organic N (b) applied (both in dark green color). Recovered residual N in terms of grain yields (first three columns of the figure) or in terms of whole-plant N uptake (last three columns of the figure) for a period of three years after a single pig slurry (PS) application is shown in the light-green columns. The numbers in the white boxes show the relative total N residual effect over the total (a) or the organic (b) N applied and are expressed as a percentage.
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Table 1. Sowing and harvesting crop dates (dd/mm/yryr) during the 10 year experimental period for the different crops.
Table 1. Sowing and harvesting crop dates (dd/mm/yryr) during the 10 year experimental period for the different crops.
Growing Season2000/012001/022002/032003/042004/052005/062006/072007/082008/092009/10
CropBarleyBarleyWheatBarleyBarleyWheatBarleyFallowWheatBarley
Sowing05/11/0008/11/0131/10/0230/10/0316/11/0404/11/0604/11/06-10/11/0803/11/09
Harvest18/06/0128/06/0226/06/0326/06/0401/07/0527/06/0626/06/07-04/07/0901/07/10
Table 2. Annual mineral nitrogen (MN) applied and single pig slurry (PS) 1 treatments at sowing. For the 2001/02 to 2009/10 cropping seasons, the points at which the first-year (RE1), second-year (RE2), and third-year (RE3) residual effects were quantified are highlighted with shaded color areas. The 2007/08 season consisted of fallow (F) without fertilization.
Table 2. Annual mineral nitrogen (MN) applied and single pig slurry (PS) 1 treatments at sowing. For the 2001/02 to 2009/10 cropping seasons, the points at which the first-year (RE1), second-year (RE2), and third-year (RE3) residual effects were quantified are highlighted with shaded color areas. The 2007/08 season consisted of fallow (F) without fertilization.
TreatmentsGrowing Seasons
2000/012001/022002/032003/042004/052005/062006/072007/082008/092009/10
MN 2
(kg of N ha−1)		0 + 300 + 300 + 300 + 300 + 300 + 300 + 30F0 + 300 + 30
30 + 3030 + 3030 + 3030 + 3030 + 3030 + 3030 + 30F30 + 3030 + 30
30 + 6030 + 6030 + 6030 + 6030 + 6030 + 6030 + 60F30 + 6030 + 60
30 + 12030 + 12030 + 12030 + 12030 + 12030 + 12030 + 120F30 + 12030 + 120
PS 3
(m3 ha−1)		20
(284/61)		RE1RE2RE320
(138/41)		RE1RE2F20
(105/27)		RE1
40
(495/117)		RE1RE2RE340
(250/83)		RE1RE2F40
(187/48)		RE1
80
(851/210)		RE1RE2RE380
(534/194)		RE1RE2F80
(424/110)		RE1
020
(179/31)		RE1RE2RE320
(143/41)		RE1FRE320
(119/33)
040
(299/57)		RE1RE2RE340
(312/83)		RE1FRE340
(239/67)
080
(498/108)		RE1RE2RE380
(633/194)		RE1FRE380
(477/133)
0020
(231/66)		RE1RE2RE320
(170/66)		FRE2RE3
0040
(402/132)		RE1RE2RE340
(290/113)		FRE2RE3
0080
(743/264)		RE1RE2RE380
(551/212)		FRE2RE3
1 From 2000–2001 to 2003–2004, annual doses of PS at sowing were complemented with 60 kg of N ha−1 year−1 at topdressing as ammonium nitrate. 2 The applied mineral treatment was ammonium nitrate (33.5% N). The first number indicates the amount of N applied at sowing and the second one, the amount applied at cereal tillering (kg of N ha−1). 3 The numbers in brackets equal the total amount of N applied (kg of N ha−1) and the organic N applied (kg of N ha−1), respectively, in each cropping season.
Table 3. Chemical parameters (over fresh weight) of pig slurry applied from 2000 to 2009 at sowing, except for the 2003/04 cropping season (full residual) and the 2007/08 fallow season.
Table 3. Chemical parameters (over fresh weight) of pig slurry applied from 2000 to 2009 at sowing, except for the 2003/04 cropping season (full residual) and the 2007/08 fallow season.
Parameter20002001200220042005200620082009Mean
pH (1:2.5)8.07.77.88.78.68.38.28.78.3
DM (g kg−1)83351059410978809384
Total N (kg of N m−3)8.34.76.88.88.98.17.36.77.7
NH4+-N (kg of N m−3)6.13.64.26.16.95.05.45.05.4
Organic N (kg of N m−3) 2.21.12.62.72.03.11.91.72.3
Table 4. The grain yield and whole-plant N uptake (kg ha−1) response curves 1 to mineral N fertilization applied in each cropping season (year) as ammonium nitrate (33.5%) at rates ranging from 0 to 150 kg of N ha−1 (x).
Table 4. The grain yield and whole-plant N uptake (kg ha−1) response curves 1 to mineral N fertilization applied in each cropping season (year) as ammonium nitrate (33.5%) at rates ranging from 0 to 150 kg of N ha−1 (x).
YearGrain Yield (kg ha−1)R2Whole-Plant N Uptake (kg ha−1)R2
2000/01Y = 2575.12 + 25.0437x − 0.119107x20.68Y = 65.38 + 1.07x − 0.00438x20.76
2001/02Y = 2708.08 + 26.716x − 0.136887x20.58Y = 56.39 + 0.87x − 0.00326x20.84
2002/03Y = 1765.75 + 15.3512x − 0.0762058x20.61Y = 30.66 + 0.54x − 0.00097x20.83
2003/04Y = 2313.07 + 33.9637x − 0.178394x20.91Y = 65.34 + 0.69x − 0.00269x20.56
2004/05Y = 1215.7 + 11.8717x − 0.0739383x20.69Y = 29.37 + 0.36x − 0.00134x20.64
2005/06Y = 2182.53 + 11.166x − 0.0325398x20.91Y = 67.00 + 0.55x − 0.00202x20.51
2006/07Y = 1921.3 + 31.7152x − 0.201552x20.84Y = 40.76 + 1.21x − 0.00598x20.91
2007/08Fallow period-Fallow period-
2008/09Y = 4599.93 + 30.0266x − 0.164394x20.63Y = 123.41 + 2.23x − 0.01069x20.55
2009/10Y = 3238.4 + 79.0387x − 0.371552x2 0.86Y = 52.93 + 2.27x − 0.01235x20.84
1 All response curves were significant (with p-values of < 0.001).
Table 5. Mineral N fertilizer equivalence (MNFE) values after specific pig slurry (PS) applications at rates of 20, 40, and 80 m3 ha−1 based on grain yield and whole-plant N uptake at different annual harvests and after the first (Yr1), second (Yr2), and third (Yr3) year (harvest) after slurry application.
Table 5. Mineral N fertilizer equivalence (MNFE) values after specific pig slurry (PS) applications at rates of 20, 40, and 80 m3 ha−1 based on grain yield and whole-plant N uptake at different annual harvests and after the first (Yr1), second (Yr2), and third (Yr3) year (harvest) after slurry application.
YearPS RateMNFE Based on Grain Yield 1MNFE Based on Whole-Plant Nitrogen Uptake
 (m3 ha−1)(kg of N ha−1)(kg of N ha−1)
200220042007201020022003200420052006200720092010
Yr12028.72.724.36.522.317.10.0-25.511.9-5.2
4055.820.236.721.939.421.72.6-49.844.7-14.3
80121.354.969.431.7124.646.035.4-240.152.1-23.3
Yr220-11.218.0--14.90.00.0-17.819.8-
40-12.627.2--31.23.314.8-9.326.3-
80-20.840.4--38.00.0Nd-17.346.7-
Yr320-16.1-0.0--0.026.53.5-27.70.0
40-5.6-6.8--0.77.723.4-16.06.2
80-19.3-35.5--6.813.138.9-50.125.1
1 No significant mineral N fertilizer response to the grain yield was observed in the 2002–2003, 2004–2005, 2005–2006, and 2008–2009 cropping seasons. Nd: no data.
Table 6. Relative residual N effects (REs) over the total N and over the organic N (%) of a single pig slurry (PS) application at the rates of 20, 40, and 80 m3 ha−1 and according to the grain yield (GY) 1 and the whole-plant N uptake (WPNU) for the different annual harvests. The RE was calculated for the first (Yr1), the second (Yr2), and the third (Yr3) year after slurry application.
Table 6. Relative residual N effects (REs) over the total N and over the organic N (%) of a single pig slurry (PS) application at the rates of 20, 40, and 80 m3 ha−1 and according to the grain yield (GY) 1 and the whole-plant N uptake (WPNU) for the different annual harvests. The RE was calculated for the first (Yr1), the second (Yr2), and the third (Yr3) year after slurry application.
YearPS RateRE Based on GYRE Based on WPNU
(RE) (m3 ha−1)(%, Over Total N Applied)(%, Over Total N Applied)
2002200420072010Mean20022003200420052006200720092010Mean
Yr12010.11.116.96.78.77.99.60.0-20.89.1-5.68.8
(RE1) 4011.35.012.211.710.07.97.30.6-19.914.9-7.69.7
8013.87.411.08.310.114.49.34.8-42.98.3-6.014.3
Yr220-6.214.7-10.4-5.20.00.0-14.613.2-6.6
(RE2) 40-4.210.8-7.5-6.31.13.7-3.69.1-4.8
80-4.27.8-6.0-4.30.0Nd-3.38.5-4.0
Yr320-5.7-0.02.8--0.014.81.5-19.60.07.2
(RE3) 40-1.1-2.21.7--0.12.66.0-4.62.13.1
80-2.2-6.44.3--0.82.65.2-7.44.54.1
YearPS RateRE Based on GYRE Based on WPNU
(RE)(m3 ha−1)(%, Over the Organic N Applied)(%, Over the Organic N Applied)
2002200420072010Mean20022003200420052006200720092010Mean
Yr12047.13.858.226.533.936.555.60.0-68.731.4-21.935.7
(RE1) 4047.815.445.845.338.633.738.11.8-65.755.9-29.537.4
8055.221.035.932.136.158.442.813.7-141.427.0-23.351.1
Yr220-36.348.3-42.3-24.40.00.0-48.037.8-22.1
(RE2) 40-22.135.6-28.8-26.75.811.7-12.024.3-16.1
80-19.325.5-22.4-16.80.0Nd-10.821.2-12.2
Yr320-26.3-0.013.2--0.086.05.5-67.50.031.8
(RE3) 40-4.8-5.25.0--0.613.418.7-17.15.311.0
80-8.5-16.612.6--3.111.914.7-23.511.813.0
1 No significant mineral N fertilizer response to the grain yield was observed in the 2002/03, 2004/05, 2005/06 and 2008/09 cropping seasons. Nd: no data.
Table 7. Nitrogen use efficiencies (NUEs) for different rates of pig slurry (PS) 1 applied in the cropping season (Yr0). New NUE values, obtained after the first (Yr0+1), second (Yr0+1+2), and third (Yr0+1+2+3) year following the slurry application, are also included 2.
Table 7. Nitrogen use efficiencies (NUEs) for different rates of pig slurry (PS) 1 applied in the cropping season (Yr0). New NUE values, obtained after the first (Yr0+1), second (Yr0+1+2), and third (Yr0+1+2+3) year following the slurry application, are also included 2.
TimePS RateNUEs at Different Harvests
(m3 ha−1)2001200220032004 3200520062007200820092010
Yr0200.280.500.27-0.310.620.32Fallow2.030.50
400.170.370.22-0.220.360.25Fallow1.000.42
800.130.220.13-0.120.180.17Fallow0.730.26
Yr0+120-0.540.691.00-0.831.05Fallow-2.64
40-0.360.530.77-0.570.61Fallow-1.45
80-0.280.330.38-0.350.32Fallow-0.97
Yr0+1+220--0.671.001.65-1.23Fallow1.46-
40--0.450.761.22-0.76Fallow0.85-
80--0.330.45Nd-0.46Fallow0.49-
Yr0+1+2+320---0.841.202.62-Fallow-1.77
40---0.570.861.87-Fallow-1.05
80---0.400.52Nd-Fallow-0.67
1 The N rates for each cropping season are defined in Table 2. 2 The N uptake in the new NUE values include the residual effects on the whole-plant N uptake (WPNU) from the cropping seasons after the slurry application. They are added to the WPNU of the year of application. The nitrogen applied at Yr0 was maintained in the calculations. 3 Nitrogen fertilization was not applied in the 2003–2004 cropping season. Nd: no data.
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Ortiz, C.; Boixadera, J.; Bosch-Serra, À.D. Residual Effects of Pig Slurry Fertilization in a Mediterranean Rainfed Cereal System. Agronomy 2024, 14, 2552. https://doi.org/10.3390/agronomy14112552

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Ortiz C, Boixadera J, Bosch-Serra ÀD. Residual Effects of Pig Slurry Fertilization in a Mediterranean Rainfed Cereal System. Agronomy. 2024; 14(11):2552. https://doi.org/10.3390/agronomy14112552

Chicago/Turabian Style

Ortiz, Carlos, Jaime Boixadera, and Àngela D. Bosch-Serra. 2024. "Residual Effects of Pig Slurry Fertilization in a Mediterranean Rainfed Cereal System" Agronomy 14, no. 11: 2552. https://doi.org/10.3390/agronomy14112552

APA Style

Ortiz, C., Boixadera, J., & Bosch-Serra, À. D. (2024). Residual Effects of Pig Slurry Fertilization in a Mediterranean Rainfed Cereal System. Agronomy, 14(11), 2552. https://doi.org/10.3390/agronomy14112552

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