Effect of sole and conjunctive applications of plant residues and inorganic nitrogen on growth, yield ad N uptake of sorghum.

Abstract

Conjunctive use of organic and inorganic sources of nitrogen is a pragmatic approach for increasing crop productivity while maintaining or improving soil quality. Field experiments were conducted to optimize the conjunctive use of sorghum straw and gliricidia 'loppings with urea for supplying nitrogen to sorghum grown in dryland Alfisols during the kharif seasons of 1994 and 1995 with 13 treatments and 3 replications in a randomized block design. Treatments consisted of 'sole and conjunctive applications of urea and plant residues, viz. sorghum straw and gliricidia loppings to supply N equivalent to the recommended dose of 60 kg her1 to rainfed sorghum. Crop growth, yield and N uptake were recorded. In the initial stages of crop growth, drymatter production Was higher with 100% N through urea treatment, but with the progress of crop age, urea + gliricidia treatments produced equal or greater drymatter and grain yield. Application of sorghum straw caused reduction in drymatter production and grain yield. Nitrogen uptake by the crop also showed similar trends. Nitrogen uptake at maturity was distinctly higher with gliricidia treatments compared to 100% N through urea. Agronomic efficiency and apparent recovery of applied N were higher with gliricidia treatments and lower with sorghum straw at equivalent N level. Negative efficiency and recovery were observed with 100% N through sorghum straw treatment. The results indicate that gliricidia can be used as a source of N to crops, solely or in combination with inorganic N, whereas sorghum straw can not be used as a source of N, even in combination with inorganic N.