The effect of cotton, maize, wheat and alfalfa residues on soil ammonium and nitrate concentrations

This study was conducted to investigate the effects of crop residues on mineral nitrogen rates of soil using four crop residues of cotton، maize، wheat and alfalfa، urea treatment (90 kg/ha) and control based on completely randomized block design with four replications. N fertilizer (urea) was added to residues، in terms of C/N ratio and calculation of nitrogen factor، before incorporating them into the soil to eliminate immobilization. Values of nitrate and ammonium were measured in different stages including tillering، stem elongation، booting، anthesis and physiological ripening. Total N released from alfalfa and wheat residues were 74. 66 and 68. 23 kg/ha، respectively. Total N mineralized from crop residues was not significant compared with urea treatment. In stage by stage analyses، the lowest and the highest values of total N were obtained in anthesis and booting stages، respectively. Total mineralized N released from crop residues and urea treatment was not significant. Totally، results revealed that if the trend of N releasing time from residues was matched with crop demand pattern، crop residues could be considered as an appropriate source for providing nitrogen.