Integrated nitrogen management in rice (Oryza sativa)-wheat (Triticum aestivum) cropping

A field experiment was conducted during 1996-97 and 1997-98 to evaluate the effect of 4 organic sources of nutrients along with 4 levels of N to rice (Oryza sativa L.) and 4 levels of fertilizer N to wheat (Triticum aestivum L. emend. Fiori & Paol.) on the productivity and nutrient removal in rice-wheat system. Grain yields of rice obtained at 40 kg N/ha with green-manuring of Sesbania was similar to that obtained with application of 120 kg N/ha under cowpea [Vigna unguiculata (L.) Walp.] fodder, wheat straw incorporation and the control, indicating a saving of 80 kg N/ha. Application of 120 kg N/ha to wheat grown in Sesbania green-manured rice plots yielded about 0.6 tonne/ha more wheat grain than that only with 120 kg N/ha. However, integrated use of Sesbania green manure along with 120 kg N/ha gave 6.8 tonnes/ha of rice grain and subsequent application of 120 kg N/ha to succeeding wheat crop yielded 4.7 tonnes/ha of wheat grain, thus giving total production of 11.5 tonnes/ha from rice-wheat sequence. At this production level and fertilizer use, rice removed 155.7, 27.7 and 172.4 kg N, P and K/ha and respective values for wheat were 126.2, 24.3 and 140.0 kg/ha, making a total removal of 646.3 kg nutrients (MPK)/ha/annum from rice-wheat system.