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Crop residue management is posing a serious problem in the rice (Oryza sativa)±wheat (Triticum aestivum) cropping system, which is widely practised in the Indian Subcontinent and China, and covers about 22.5 6 10 6 ha. The problem is serious because there is very little turn-around time between rice harvest and wheat sowing. Three practices, namely, residue removal, residue burning and residue incorporation were compared in two ®eld experiments, one with the rice residues and the other with the wheat residues. Results obtained showed that both rice and wheat residues can be safely incorporated without any detrimental eects on the crops of rice or wheat grown immediately after incorporation. Incorporation of crop residue also improved soil fertility status as judged by organic carbon and available phosphorus and potassium contents. Residue incorporation should be preferred over residue burning, which results in the loss of valuable plant nutrients and is both an environmental and a health hazard.

A field experiment was conducted during 2006 and 2007 (June- December) at New Delhi to assess the performance of three cotton hybrids of which two Bt (MRC 6304 & RCH 317) and one non-Bt cotton hybrid LHH 144 (North zone check) in response to nitrogen fertilization (0, 60, 120 and 180 kg ha-1). Based on pooled analysis, both Bt hybrids produced similar seed cotton yield (SCY). Bt hybrid have produced 7.1 bolls/plant (on an average) and bolls 0.48 g heavier than non Bt hybrid LHH 144 that lead to 1.07 t ha-1 higher SCY of Bt hybrids than non-Bt hybrid (1.93 t ha-1). Though the N uptake by cotton hybrids was statistically similar N harvest index (NHI) was higher in Bt hybrid (57.85) as compared to non-Bt hybrid (40.5). The agronomic N use efficiency (ANUE) was highest in MRC 6304 Bt (6.44) and least in LHH 144 non-Bt cotton (3.91). Cotton growth, yield attributes, SCY, and N uptake increased with each successive increase to the highest level of 180 kg ha-1 however, the N response of cotton was quadratic in nature with optimum dose of 173.0 kg ha-1. The NHI decreased with increase in N dose i.e. from the highest of 56.3 in control to the lowest of 48.8 with 180 kg ha-1 N fertilization. ANUE and physiological NUE that was highest with 60 (5.73) and 120 kg N fertilization (17.05), respectively and decreased with further increase in N dose. The cotton hybrid x N interaction effect revealed that Bt cottons have quadratic N response while non-Bt cotton has linear N response. From the economic point of view, Bt hybrids with 120 kg Nha-1 could be optimum dose for cotton cultivation. DOI: http://dx.doi.org/10.3329/sja.v11i1.18389 SAARC J. Agri., 11(1): 121-132 (2013)

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