G. Subba Reddy

Prediction of nitrogen availability in soil after crop residue incorporation

Controlled study was conducted with five farm-based organic residues to predict the expected nitrogen availability with time, based on N concentration and C/N ratio of the residues under two moisture availability situations. Two kg of red loamy sand soil representing Alfisol and related soil was incubated with the residues to supply 40 kg N ha−1 at 28 ± 1°C at field capacity (FC) and 50% FC moisture conditions. Results obtained indicated that N content in soil released from residues increased with the time allowed for decomposition reactions at both FC and 50% FC moisture regimes. Relatively higher amount of N release was observed in case of legume residues like mungbean (Vigna radiata),L. leucocephala and perennial pigeonpea (Cajanus cajan), although the rate of N release was more with low N concentration residues. Sorghum stover with C/N ratio of 72.1 resulted in immobilization of N upto 90 days. Nitrogen release was higher at FC than 50% FC. The critical N concentrations of the residues at which N neither released nor immobilized decreased with the length of incubation. At 50% FC the critical concentrations were higher than at FC.

Green leaf manuring as an alternative nitrogen source for castor bean on marginal soils of India

Chemical fertilizers are used only in a limited way under dry farming conditions in India because of their high cost and the risk of crop failures due to drought Several alternative strategies are being evaluated to reduce the cost of supplying N to castor bean without adversely affecting yield. We report the results of a two-year study on the possible replacement of fertilizer nitrogen by green leaves from Leucaena leucocephala for production of castor beans on a low fertility Alfisol Bean yield and dry matter production were significantly higher when 50 kg N/ha was applied as green leaves compared with 50 kg N/ha as urea. Among substitution levels, 37.5 kg N/ha as green leaves at planting followed by 12.5 kg N/ha as urea at 45 days after planting was found to be the most effective combination. Across all the substitution levels, addition of nitrogen as green leaves at planting was found to be better than application at 45 days after planting. Nutrient and water use efficiencies were higher when the N was applied as green leaves compared to urea. Nitrogen use efficiency was higher for green leaves than for urea under limited rainfall conditions. The overall data indicated that 75 percent of the fertilizer N requirement of castor bean can be supplied by leaves of Leucaena leucocephala when applied at planting .