Effect of organic matter supplementation on nitrogen transformations in soils. II. Nitrogen balance and yield.

Under controlled laboratory conditions, the effect of the application of uncomposted plant materials (sawdust and maize stalks) or horns and hooves (narrow C/N ratio) on soil nitrogen and plant growth was investigated. From nitrogen balance calculations it was found that the addition of the wide C/N ratio materials alone either increased soil nitrogen through N2-fixation or lessened nitrogen loss through denitrification. Although such materials resulted in the immobilisation of mineral nitrogen, no nitrogen starvation symptoms were noted on the growing plants. Negative nitrogen balances were usually obtained when soils received mineral nitrogen fertilizers either alone or together with maize stalks or supplemented with the narrow C/N ratio organic material.