The effect of crop residues on soil nitrogen dynamics and wheat yield

Abstract

The effects of different kinds of crop residues on cereal yield and nitrogen uptake have not been studied. A two-year (2008-2010) field experiment was aimed to study the effect of four crop (cotton, alfalfa, wheat and maize) residues with different C:N ratios and compare them with pure urea and a control treatment, on soil N concentration (as nitrate + ammonia) and total N accumulation in the leaves and stem of wheat (cv. N8019, a high N-demanding cultivar). For this purpose, immobilization was avoided by adding N as urea to residues based on their C:N ratio and nitrogen index, which was established at 90 Kg N.ha -1 . Soil and plant nitrogen were measured in six phenological stages. The maximum yield difference between residues and the control treatment was 1.7 ton ha -1 in the alfalfa residue. The highest nitrate and ammonia concentration in the soil (74.1 kg ha -1 ), the greatest consistency between nitrate and ammonia release with crop demand (from tillering to stem elongation) and the highest increase in yield per 1 kg of added N (29.14 kg grain ha -1 kg -1 N) also characterized the alfalfa residue. Overall, treatments had affected wheat grain yield, leaf area index and 1000-grain weight, but did not affect grain number spike -1 . The highest grain yield (7.25 ton ha -1 ) and 1000-grain weight (50.36 g) were also obtained when alfalfa residue was applied, although all residues resulted in higher yield than the control plot. Wheat residues did not perform well compared to other residues. Since other residues performed worse than alfalfa but performed better than the wheat residue, their use in the field should be carefully considered.