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Abstract

A three-year chickpea-wheat rotation study was carried in a well-drained sandy soil at National Agricultural Research Centre, Islamabad, to quantify nitrogen fixation by chickpea and determine its residual N effects on soil N-fertility and yield of following wheat crop. The treatments were; continuous wheat without N, continuous wheat with N, chickpea wheat rotation without N (to wheat), chickpea wheat rotation with N (to following wheat), and continuous chickpea. In N treatments, nitrogen was applied to wheat @ 100 kg ha-1. The δ15N of shoot of chickpea and non-nitrogen fixing reference crop (wheat) was used to determine the percentage of chickpea N derived from nitrogen fixation (pfix). The pfix values by chickpea ranged from 70-98%. The total N fixed by chickpea ranged from 64-103 kg N ha-1 in 996/97 and 138 kg ha-1 in 1997/98. After removal of above ground biomass of chickpea at harvest, the average N balance in our study was 38 kg N ha-1 and 35kg N ha-1 after first and second years. Continuous wheat grown without N fertilizer (control) exhausted soil N fertility and produced the least grain yield. Wheat sown after chickpea with N application produced the highest grain yield followed by continuous wheat with N. Chickpea rotation also increased significantly the yield by 11% of following wheat without N treatment. Continuous chickpea crop and its rotation with wheat enhanced N fertility level of the soil. Our results support the strategy of using legumes in rotation with wheat in the arid region for enhancing soil N-supply and increasing wheat yield.

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