Residual effect of blackgram (Phaseolus mungo) in maize (Zea mays)-blackgram cropping sequence in Ultic Hapludalf of Assam

An experiment was conducted during 1997-99 to study residual effect of blackgram (Phaseolus mungo L.) with straw incorporation on the proceeding rainy-season maize (Zea mays L.) in maize-blackgram crop rotation in Ultic Hapludalf in the hill region of Assam. Significant residual effect of blackgram in terms of N and P was recorded in rainy-season maize. Grain yield of rainy-season maize (with blackgram rotation) with 50% recommended N and P ( 30 kg N/ha and 9.7 kg P/ ha) was found to be significantly higher (4 347 kg/ha) than that of sole maize (2 462 kg/ha) with 100% recommended N and P (60 kg N/ha and 19.4 kg P/ha), but at par with that of sole maize at 150% recommended N and P. Residual effect of blackgram on rainy-sea on maize was equivalent to 60 kgN/ha and 17.6 kg P/ha. Higher fertilizer-use efficiency (10.22 kg grain/kg N and P) and productivity (4 288 kg/ha) of rainy-season maize (with blackgram rotation) than that of sole maize (5.79 kg grain/kg NPK and 3 124 kg/ha respectively) were also recorded. Residual effect of blackgram on succeeding maize in terms of P was higher in the second year of crop rotation. Response of maize in terms of grain yield decreased with increase in levels of P in the second year of crop rotation. Benefit : cost ratio as well as fertilizer-use efficiency of rainy-season maize (with blackgram rotation) were highest (5.49 and 13.51 kg grain/kg N and P respectively) with treatment combination of 75% recommended N + 50% recommended P. Blackgram rotation (with straw incorporation) enhanced total N and available P by 202 and 23 kg/ha respectively. In addition, soil pH, organic matter content and water-holding capacity were also enhanced from 6.02 to 6,12, 1.86 to 2.16% and 33.3 to 36.5%, respectively, by blackgram rotation in hill region of Assam.