Field experiment was conducted in an experimental soil belonging to Kalathur series in Cauvery Delta in the rice-rice-pulse system to evaluate the influence of Optimum Nutrient Treatment evolved on the basis of nutrient sorption studies and experimental soil initial analysis, on the yield in rice and to study the subsequent residual effect of the imposed treatments on the yield of blackgram. The results of the experiment revealed that considerable amounts of residual N, P and K were left in the soil due to application of N, P and K fertilizers to the kwuvai and thaladi season rice crops. This was evidenced in the enhancement of grain and haulm yields of blackgram due to N or P or K fertilization. Zn omission from the ONT did not attain statistical significance in its influence on blackgram yield. Blanket fertilizer application reduced the yield of nutrients. Economics of fertilization also revealed the usefulness of the optimum nutrient treatment over the blanket recommendation.
