RESPONSE OF NITROGEN FERTILIZATION ON BT AND NON-BT COTTON (Gossypium hirsutum) HYBRIDS
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)
Square formation, boll retention, yield and quality parameters of Bt and non-Bt cotton in relation to plant density and NPK levels
A Two year experiment was conducted to study the effect of plant densities and NPK levels on Bt and non-Bt cotton in split plot with four replications. The result shows that non-Bt cotton produced taller plant, more monopodia and sympodia, higher leaf area index (LAI). Whereas, Bt cotton had maximum specific leaf weight (SLW), net assimilation rate (NAR), square formation rate (SFR), fruit production efficiency (FPE), boll retention efficiency (BRE), boll growth rate, yield attributes and thus produced higher seed cotton yield than non-Bt. Bt cotton minimized the boll maturation period and impart earliness in cotton. The Bt cotton enhanced ginning out turn whereas, staple length and micronaire value remained higher in non-Bt. As regards plant density, spacing of 90x60cm recorded more monopodia and sympodia, maximum SLW, NAR, SFR, BRE, picked bolls and seed cotton yield per plant than 90x45cm. On contrary higher plant density under 90x45cm spacing increased plant height, LAI, FPE and seed cotton yield per ha. Each increased level of NPK significantly increased plant height, number of monopodia, sympodia and LAI over lower level. The application of 75:37.5:37.5kg NPK ha significantly increased SLW, NAR, SFR, FPE, BRE, boll growth rate, boll weight, picked bolls, seed cotton yield per ha and augment the lint quality traits like uniformity ratio and micronaire value over lowest level of NPK i.e. 50:25:25kg NPK ha. However, lowest level of NPK improved the lint elongation.
Do slow‐growing species and nutrient‐stressed plants consistently respond less to elevated CO2? A clarification of some issues raised by 
 Poorter 1998 )
Lloyd & Farquhar (1996) addressed the effect of elevated [CO2] on the relationships between photosynthesis, plant growth and their interaction with soil nitrogen availability. Using a quantitative approach the contrasting nature of photosynthetic vs. growth responses to elevated [CO2] was discussed. The importance of genetic and environmental differences in plant respiratory costs was also emphasized. In examining the importance of variation in soil nitrogen availability in modulating [CO2]±growth relationships it was concluded, contrary to the widely held assumption at the time, that plant growth enhancements in response to elevated CO2 concentrations were `nearly as often as not greater under low nutrient conditions' (Lloyd & Farquhar 1996; p. 8). A simple model of plant growth in relation to carbon and nitrogen availability accounting for this observation was then presented. In passing, likely effects of higher respiratory costs in slower growing plants on their growth response to elevated [CO2] were also mentioned. Recently Poorter (1998) has suggested that the model of Lloyd & Farquhar (1996) is `not supported by the available data' and that `plant growth at low nutrient supply or high CO2 concentrations is not constrained by C-availability'. Here we show why some of the issues and hypotheses advanced in his paper may be ̄awed.