Management practices of antecedent leguminous and non-leguminous crop residues in relation to winter wheat yields, nitrogen uptake, soil nitrogen mineralization and simple nitrogen balance

Many studies have been conducted in examining the effects of N fertilizers on cereal yields and nitrogen (N) uptake, the effects of different kind of crop residues and their management practices on cereal yield, nitrogen uptake and simple N balance have not been studied extensively. We studied the effects of antecedent leguminous (white clover and field pea) and non-leguminous (perennial ryegrass and winter wheat) crop residues, each subjected to four different residue management practices (ploughed, rotary hoed, mulched and burned) on grain yield, nitrogen uptake by succeeding winter wheat crops, soil N mineralization and simple N balance. Grain yield and N uptake by the first wheat crop were significantly higher under leguminous than non-leguminous residues, following the order of white clover>pea>ryegrass>wheat. Grain yield under the mulched treatment was significantly lower than those of other management treatments due to lower plant population established. While N uptake was significantly lower under rotary hoed and mulched treatments as compared to other treatments, mulching had a positive residual effect on the grain yield of second wheat crop. Similar to grain yield, total soil N mineralization was greater under leguminous residues during the growing period of first wheat crop and was significantly correlated with C/N ratio of the residues. The calculated simple N balance showed that positive N balances occurred under white clover after one wheat crop when N inputs from only crop residue tops was considered. This also occurred even after two wheat crops when total N inputs from crop residues (tops+roots) were considered. However, with pea, the positive N balance occurred only after the first wheat crop when total N input from crop residues (tops+roots) were considered. These calculations demonstrated the important contribution of root-N to the N economy of the cropping system, which was largely ignored in most studies. The burning of residues showed no significant advantage over other residue management treatments. This was also evident from N balance calculations, which showed, in general, N balance was lower or more negative under residue-burned treatment as compared with other treatments. Overall, present results showed that it is beneficial to retain crop residues in the field, even though non-leguminous residues may cause substantial soil N immobilization initially reducing N availability to the first wheat crop, this N eventually became available to subsequent wheat crops and also increase the fertility of soils in the long-term. Thus, N inputs from crop residues are far more beneficial to the cropping system as compared to the burning of crop residues in the field or their removal from the field.