Abstract
Excessive nitrate leaching represents a potential groundwater contamination. This study was carried out in an experiment area located in the city of Piracicaba/SP- Brazil, on a sandy-clayey loam soil. The objective was to evaluate internal drainage and nitrate leaching at the depth of 0.80 m in a crop succession, using 15N-labeled ammonium sulfate, in two split N applications. Evaluations were based on two corn crops, the first grown during the 2003/2004 cropping season, and the second in the 2004/2005 season, and on a black oat crop grown during the off-season. Treatments consisted of a single 120 kg N ha-1 rate, in the form of labeled (15N) ammonium sulfate, and two split N applications at 30-90 and 60-60 kg N ha-1. The fertilizer was applied in previously-defined subplots, in the first corn cultivation only (2003/04 cropping season). Evaluations included: soil physical and water content characterization; water flux density in the soil, and nitrate leaching at a 0.80 m depth; nitrogen in the soil solution derived from the fertilizer and 15N recovery by the soil solution at the end of the corn and black oat crop cycles. Loss by leaching in the 1st corn cultivation was approximately 96 and 68 kg ha-1 nitrate, for treatments with 60 kg ha-1 and 30 kg N ha-1 applied at seeding, respectively, of which only 3 and 1 kg ha-1 were from the nitrogen fertilizer.
Highlights
Leaching is the translocation of soluble salts that occurs via a descending flux of water in the soil profile (Kiehl, 1987)
In studies on N fertilization (20 and 200 kg N ha-1) in corn with two types of management was verified that, during 30 years of simulation, nitrate losses by leaching were higher in plots where the residues were removed from the soil, when compared with plots where residues were returned to the soil (Gollany et al, 2005)
A precipitation increase of 41 mm occurred in the 2nd corn cultivation in relation to the 1st (Figure 2), this did not imply greater crop development
Summary
Leaching is the translocation of soluble salts that occurs via a descending flux of water in the soil profile (Kiehl, 1987). Years of 1978 and 1999, and observed that in 78% of the experiments conducted in different soils and crops, fertilized on average with a rate of 92 kg N ha-1, the total N losses by leaching were small, 1.26 kg N ha-1, on average. N losses by leaching can be controlled by splitting the application of nitrogen fertilizers, especially during high precipitation periods. In studies on N fertilization (20 and 200 kg N ha-1) in corn with two types of management (harvested residues or returned residues) was verified that, during 30 years of simulation, nitrate losses by leaching were higher in plots where the residues were removed from the soil, when compared with plots where residues were returned to the soil (Gollany et al, 2005). The amount of N lost by leaching varies significantly depending on the N rate, fertilizer application method, amount of rainfall, and soil properties (Kiehl, 1987)
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