Pig slurry versus mineral fertilization on corn yield and nitrate leaching in a Mediterranean irrigated environment

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Abstract

Over the last 20 years, in many regions of Spain, there has been an intensification of pig production. Most of the resulting pig slurry (PS) is applied to agricultural fields and so it is important to determine the availability of nitrogen for the crops and to assess the risk of adverse environmental effects such as nitrate leaching. The effects of a single application of three different doses of PS: 50, 100 and 150 m3 ha−1, were compared with a control mineral treatment in an irrigated Mediterranean environment. Development and crop yield of corn and the amount of nitrate leached were evaluated during 3 years in a Typic Xerofluvent soil. No significant differences for aboveground biomass, corn yield and nitrogen plant uptake were observed between the different fertilization schemes. Nitrate concentrations in the soil solution at the 0.9–1.2 m depth were higher for the control treatment (44.7 mg NO3N l−1) than for the slurry treatments (ranging from 19.9 to 28.0 mg NO3N l−1), indicating a higher susceptibility to nitrate leaching for the control mineral treatment. The high unaccounted losses in the N budget for the slurry treatments and the unexpectedly decrease in the ratio between nitrate leaching and applied nitrogen with increased N doses proves that there is a need to examine the slurry N cycle in the soils with especial emphasis in the immobilization of ammonium slurry in Mediterranean conditions.

Introduction

After Germany, Spain is the second European country in swine population (22.4 million heads in 2000), representing 18% of the total production in the European Union, with a strong growth of more than 40% over the last 10 years. Northeast Spain (Cataluña and Aragon) is clearly one of the main regions of intensive pig production in Spain, with 40% of Spain's total swine population, representing one of the most important economic and social sectors for these regions.

For many years farmers have spread pig slurry (PS) on farmland mainly as a means of waste disposal, using high spread rates with a significant risk to environmental pollution. Thus PS should be considered an important potential source of nitrogen (N) in these areas with high swine population. Of course, manure nutrient behaviour must be known in order to design the efficient management application practices that are essential to improve the economics of crop production as well as to minimise its adverse impact on water and soil quality. Many studies indicate that adequate PS applications can achieve satisfactory yields, substituting mineral fertilizers partially or completely (Brechin and McDonald, 1994, Petersen, 1996, Zebarth et al., 1996, Jensen et al., 2000). But, N losses due to inadequate PS management can contribute to nitrate (NO3) contamination of groundwater and reduce the profit margin (Sieling et al., 1998). Moreover, many studies have shown that there is an increased risk of NO3 leaching when soils receive high levels of liquid manure (Nielsen and Jensen, 1990, Beckwith et al., 1998, Jensen et al., 2000). It has been observed, however, that PS applied at adequate rates leach smaller or similar amounts of NO3 than when using mineral fertilizers (Beauchamp, 1986, Dı́ez et al., 2001).

Most studies on the use of PS as fertilizer have been carried out on northern European countries where soils and climatic conditions are very different from those found in Mediterranean areas. However, crop N requirements and the processes involved in the N cycle are sensitive to soil properties, climatic conditions and management practices (Zebarth et al., 1996).

Also, the risk of NO3 contamination increases with irrigation. But irrigation is absolutely necessary for the profitable production of crops such as corn in most regions of Northeast Spain. The risk of nitrate contamination is further increased by surface irrigation, generally shown to be inefficient (Faci et al., 2000), and a method widely used in the region.

So, the objectives of this study have been to evaluate the effect of different PS doses in comparison to a control mineral N treatment on, (1) the development and yield of a maize crop, (2) the evolution of inorganic N concentrations in the soil, (3) the amount of NO3 leached, and (4) the N budget of the system in a Mediterranean surface irrigated environment.

Section snippets

Field experiment

The study was conducted on the experimental farm of the Agronomic Research Service of the Government of Aragon in Zaragoza, on a Typic Xerofluvent, silty clay loam-textured soil (Table 1) during the years 1996–1998 in a corn crop. The climate of the area is semiarid (Fig. 1) with high temperatures during the summer, low precipitations (350 mm annual average 1982–2002), and high winds which produce elevated evapotranspirative demand. Precipitations were higher than average during the period

Crop yield and development

No significant differences were observed between the different treatments for the number of plants and ears and the plant height. Average grain yield for all treatments was higher (Table 4) in 1996 than in 1997 and 1998 due to differences in weather conditions during those years (Fig. 1). These differences were also observed in other experiments running at the same time on the same experimental farm (Saad, 1999). No differences in corn yield and aboveground biomass were detected in each year of

Conclusions

PS application to corn, whether complemented (PS1) or not (PS2 and PS3) with mineral N had the same crop development, yield and plant N uptake as the mineral fertilizer treatment (T0) for the 3 years of the experiment. In Mediterranean environments the fertilizer value of PS is considered similar to that of inorganic fertilizers.

Nitrate leaching in the mineral treatment was equal or higher than in the slurry treatments indicating that slurry nitrogen does not contribute more than mineral

Acknowledgements

The authors thank Miguel Izquierdo and Jesus Gaudó for field management assistance. This study was funded by the Spanish Institute of Agricultural Research and Technology (INIA), Project SC95-031.

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