The introduction of transgenic cotton (Bt-cotton) for controlling bollworms has resulted in increased production; however, the residual effects of mulches from Bt-cotton are poorly understood. Therefore, the current study evaluated the impact of Bt and non-Bt cotton mulches on soil properties, weed dynamics and yield of winter crops sown after cotton. Three different winter crops, i.e., wheat (Triticum aestivum L.), canola (Brassica napus L.) and Egyptian clover (Trifolium alexandrinum L.) and two mulch types, i.e., Bt mulch (obtained from Bt-cotton cultivars, i.e., 'CIM-616' and 'GH-Mubarik') and non-Bt mulch (obtained from non-Bt cultivars, i.e., 'CIM-620' and 'N-414') were included in the study. The mulches were applied at a rate of 2 t ha-1 before planting the winter crops. The Bt and non-Bt mulches differentially affected soil properties, weed dynamics and productivity of winter crops. The non-Bt mulches decreased the soil bulk density and penetration resistance, while increased the soil porosity. Wheat crop increased the soil porosity, pH, available N and soil organic matter content. Overall, non-Bt mulches improved the productivity of winter crops compared with Bt mulches. The toxins released by Bt mulches lowered the weed density; however, it negatively influenced soil properties (bulk density and available nitrogen) and productivity of winter crops. Therefore, appropriate crop rotation measures may be opted for the soils cultivated with Bt-cotton to conserve soil and achieve yield sustainability for the crops sown after cotton. Nonetheless, non-Bt mulches can be used for improving soil properties and productivity of winter crops.

Nitrogen (N) is one of the major limitations to crop productivity. Therefore, a field study was conducted to examine the impacts of N application strategies: N 1 -20% of N at sowing through broadcast + 79% N at mid-season through fertigation + 1% of N at flowering through foliar application, N 2 -40% of N at sowing through broadcast + 59% of N at mid-season through fertigation + 1% of N at flowering through foliar, N 3 -60% of N at sowing through broadcast + 39% of N at mid-season through fertigation + 1% of N at flowering through foliar, N 4 -80% of N at sowing through broadcast + 19% of N at mid-season through fertigation + and 1% of N at flowering through foliar and N 5 -100% of N at sowing through broadcast, on the productivity of maize hybrids (H) single cross-6142 (H 1 ) and double cross-4444 (H 2 ) over a 2-year period, 2010-2011. During both years, N strategies and maize hybrids differed significantly for all the observed traits of yield and quality. The highest biological yield (16.99-17.62 t ha -1 ) and grain yield (6.83-7.16 t ha -1 ) were recorded by using the strategy N 3 . Similar trends were also observed for other traits except the grain oil content which was the maximum (3.38-3.98%) at N 5 . However, in both years, maximum biological yield (14.83-15.69 t ha -1 ) and grain yield (5.01-6.02 t ha -1 ) were evident in H 1 . the interactive effect of H 1 × N 3 gave maximum biological yield (17.55-20 t ha -1 ) and grain yield (7.53-8.83 t ha -1 ). In 2010 and 2011, the highest net income (1220-1272 USD ha -1 ) and benefit cost ratio (2.52-2.56) was also attained at H 1 × N 3 . In conclusion, our results suggested that maize productivity (grain yield up to 5.01-6.02 t ha -1 ) could be improved on economic basis (benefit cost ratio up to 2.52-2.56) by growing the single cross hybrid-6142 (H 1 ) with N application strategy N 3 .

Cotton (Gossypium hirsutum L.) is an important fiber crop in Pakistan with significant economic importance. Transgenic, insect-resistant cotton (carrying a gene from Bacillus thuringiensis (Bt)) was inducted in the cotton-based cropping systems of Pakistan during 2002, and is now sown in >90% of cotton fields in the country. However, concerns are rising that Bt cotton would decrease the productivity of winter crops (sown after cotton), leading to decreased system productivity. This two-year field study determined the impacts of transgenic (Bt) and non-transgenic (non-Bt) cotton genotypes on the productivities of winter crops (i.e., wheat, Egyptian clover, and canola), and the overall productivities of the cropping systems including these crops. Four cotton genotypes (two Bt and two non-Bt) and three winter crops (i.e., wheat, Egyptian clover, and canola) were included in the study. Nutrient availability was assessed after the harvest of cotton and winter crops. Similarly, the yield-related traits of cotton and winter crops were recorded at their harvest. The productivities of the winter crops were converted to net economic returns, and the overall economic returns of the cropping systems with winter crops were computed. The results revealed that Bt and non-Bt cotton genotypes significantly (p < 0.05) altered nutrient availability (N, P, K, B, Zn, and Fe). However, the yield-related attributes of winter crops were not affected by cotton genotypes, whereas the overall profitability of the cropping systems varied among the cotton genotypes. Economic analyses indicated that the Bt cotton–wheat cropping system was the most profitable, with a benefit–cost ratio of 1.55 in the semi-arid region of Pakistan. It is concluded that Bt cotton could be successfully inducted into the existing cropping systems of Pakistan without any decrease to the overall productivity of the cropping system.