EFFECT OF IRRIGATION ON NUTRIENT BALANCE IN RICE (ORYZA-SATIVA)-BASEDCROP SEQUENCES

An experiment was conducted during 1986-87 and 1987-88 at Pusa to eval uate the irrigation requirements of different rice (Oryza sativa L.)-b ased crop sequences. There was a positive gain in nitrogen and potassi um in all the crop sequences at different levels of winter and summer irrigations but phosphorus balance was negative. Maximum nitrogen bala nce was recorded under rice-gram (Cicer arietinum L.)-greengram (Phase olus radiatus L.) (128 kg N/ha) cropping sequence, whereas maximum pot assium balance was under rice-maize (Zea mays L.)-blackgram (P. mungo L.) (184 kg K/ha). Phosphorus-balance sheet showed a loss in all the c rop sequences. Maximum loss of phosphorus was recorded under rice-pota to (Solanum tuberosum L.)-greengram (-214 kg P/ha) sequence.