| In China, the planting area percentage of transgenic insect-resistant cotton has exceeded 70% in total cotton planting area. Although the yield of transgenic insect-resistant cotton is high, premature senescence caused by potassium deficiency occurs frequently and results in low yields. The potash reserves of China are penurious. Subsequently, China imports a large quantity of K fertilizers every year. Farmers are not active to adding potassium fertilizer with high price. As an important renewable resource, straw contains abundant potassium which can replenish soil potassium. In production, the yield of wheat straw and cotton residue is 9000 and 7500 kg ha-1 in Yangtze River Valley, respectively. Therefore, application rates of wheat straw in cotton season were designated as 0,4500 and 9000 kg ha-1 (W0, W4500, W9000), and those of cotton residue in wheat season were designated as 0,3750 and 7500 kg ha-1 (C0, C3750, C7500). Finally, there were nine crop residue incorporation treatments without organic K fertilizer applied in the wheat-cotton rotation system, by the processes of independent assortment of wheat straw and cotton residue. Additionally, two independent K fertilizer treatments without crop residue incorporation were designated as 150 and 300 kg K2O ha-1 (K150 and K300), with potassium sulfate (50% K2O) applied as basal fertilizer in cotton season, and they were not applied in wheat season. This research studied crop yield formation, soil microbial activity and soil physical and chemical properties in wheat-cotton rotation system. The research results should provide a theoretical basis for effects of consecutive crop residue incorporation to soil on ecological mechanisms of cotton yield formation in the wheat-cotton rotation system and define the optimal potassium fertilization amount and fertilization method of transgenic insect-resistant cotton.The main results were as follows:1 The lint yield in the treatments with consecutive crop residue incorporation and potassium fertilization had a highly significant simple linear correlation with available potassium concentration.The consecutive crop residue incorporation treatments and potassium fertilization could improve lint yield, boll number and boll weight significantly and had no effect on lint percentage. Moreover, the consecutive crop residue incorporation treatments increased water-soluble organic carbon, available potassium concentrations, decreased NH4+-N, NO3--N concentrations, and had no influence on soil organic matter, total nitrogen, and available phosphate concentrations. Additionally, the potassium fertilization treatments increased available potassium concentrations, decreased available nitrogen concentration, and had no effect on water-soluble organic carbon, available phosphate concentrations. The lint yield in the treatment with consecutive crop residue incorporation and potassium fertilization had a highly significant simple linear correlation with available potassium concentration. Furthermore, lint yield increased with total potassium uptake increasing.2 The crop residue incorporation treatments increased soil potassium concentrations, decrease soil potassium depletion, and accelerated apparent potassium balance between soil and cropThe cotton residue incorporation treatments increased significantly wheat yield, total biomass and total K uptake. Additionally, application of wheat straw and K fertilization could significantly improved seed cotton yield, total biomass and total K uptake year by year. The W9000C7500 treatment could increase crop yield similar as the K300 treatment. Cross 3-yr apparent K balance, the W9000C7500 treatment had a positive balance at Nanjing, and a least negative balance at Dafeng. Therefore, the crop residue incorporation treatments increased soil potassium concentrations, decrease soil potassium depletion, and accelerated apparent potassium balance between soil and crop.3 Consecutive crop residue incorporation on soil could increase soil K concentrations with various forms, decrease soil K fixation capacity and rate and improve the non-exchangeable K release.Compared with cotton residue incorporation, Wheat straw incorporation could increase soil K concentrations with various forms more significantly, decrease soil K fixation capacity and rate and improve the non-exchangeable K release. The K fertilization could improve soil K condition as well. The W9000C7500 treatment had the similar effect on soil K condition as K150 and K300. Based on the variation of soil available K, consecutive crop residue incorporation could totally or partly replace K fertilizer in wheat-cotton rotation system.4 Consecutive crop residue incorporation improved the amounts of bacterial physiological groups and the activities of soil enzymes which took part in carbon, nitrogen, phosphor, potassium cycle and microbial biomass in the wheat-cotton rotation systemCompared with potassium fertilization treatments, the consecutive crop residue incorporation treatments improved the amounts of bacterial physiological groups and the activities of soil enzymes which took part in carbon, nitrogen, phosphor, potassium cycle, significantly. Wheat straw incorporation treatments had positive effects on improving soil microbial activities, however, cotton residue incorporation treatments had negative effects on organic phosphorus-decomposing bacteria amount and phosphatase activity. Generally, the consecutive crop residue incorporation treatments improved the microbial activity and the percentage of available nutrient in soil total nutrient, promoted decomposing soil organic matter and soil nutrient to be absorbed and used by crop.Overall, consecutive crop residue incorporation could totally or partly replace K fertilizer in wheat-cotton rotation system, which improved soil potassium concentrations, potassium uptake by cotton and lint yield of insect-resistent transgenic cotton. Additionally, it improved soil microbial biomass and percentage of soil available nutrient in soil total nutrient. |
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