Matching Cultivation Techniques of Transgenic Hybrid Cotton Varieties 2
3. Balanced Fertilization
Among the key agronomic practices that influence crop yield, factors such as planting density, nitrogen application rate, fertilizer management, and chemical regulation play a crucial role. Transgenic hybrid cotton exhibits a significantly higher biological yield compared to conventional varieties, which increases the demand for nutrients throughout the growing season. Therefore, it is essential to implement rational fertilizer management to ensure high-yield and stable production of insect-resistant hybrid cotton.
3.1 Fertilizer and Dry Matter Accumulation
Research indicates that dry matter accumulation varies with different nitrogen rates, but the differences between treatments with higher nitrogen levels are relatively small. When biological yield is considered, applying NPK above 187.5 kg/hm² results in diminishing returns, meaning that increasing nitrogen application beyond this level does not significantly boost yield.
3.2 Fertilizers and Individual and Population Development
As the nitrogen application rate increases, both plant height and the number of large bolls per plant rise, though the differences among treatments remain minimal. Quality indicators also improve with higher nitrogen use, especially the ratio of branches to shoots, which reaches a peak when the nitrogen rate exceeds 5.00. The leaf area index develops more efficiently at a nitrogen rate of 187.5 kg/hm², peaking during the flowering stage. However, excessively low or high nitrogen levels delay the peak of the leaf area index. Low nitrogen causes early underdevelopment, while high nitrogen leads to excessive vegetative growth, delaying the peak. The timing of the leaf area index peak aligns with the development of the "three peaches," and higher nitrogen application increases the proportion of autumn bolls.
3.3 Fertilizer and Yield Formation
Experiments show significant differences in seed cotton and lint yields across various nitrogen levels. Lint yield was notably higher with 337.5 kg/hm² of pure nitrogen compared to 112.5 kg/hm² and 37.5 kg/hm². However, no significant difference was observed between 262.5 kg/hm² and 187.5 kg/hm² of nitrogen application.
3.4 Fertilizer Management
Transgenic hybrid cotton requires higher nutrient input due to its increased biological yield. Compared to conventional varieties, it needs an additional 22.5 to 37.5 kg/hm² of pure nitrogen. A total of about 300 kg/hm² of nitrogen is recommended, with adjustments based on planting density, local soil conditions, climate, and vegetation. The lower and upper limits are 270 kg/hm² and 330 kg/hm², respectively. If plastic mulch is used, the total nitrogen rate should be increased by about 10%. Basal fertilizer should account for around 35% of the total nitrogen, with special attention given to phosphorus and potassium fertilizers. Trace elements should be applied according to soil nutrient status to maximize the potential of transgenic cotton. Due to its rapid growth, managing the balance between vegetative and reproductive growth is key. Following the principle of “full, slow, and heavy†fertilizer application helps achieve multiple fruiting stages. Sufficient basal fertilizer (about 30% of total nitrogen) ensures early growth without overgrowth. Bud-phase fertilizer should be applied 5–7 days after initial flowering, in moderate amounts. The second fertilizer application should occur about 7 days later than conventional cotton, and 2–3 root sprays should be made later. In Jiangsu Province, where boron deficiency is common, applying 4–12 kg/hm² of borax as base fertilizer can enhance early maturity and increase pre-frost flowering rates.
3.5 Application of Different Fertilizers
The choice of fertilizers for genetically modified and insect-resistant hybrid cotton depends on the specific cropping system. Practices should be tailored to soil quality, fertility levels, and cotton types.
3.5.1 Soybean (Maize) Cotton Intercropping
In high-fertility fields with good soil structure, 300 kg/hm² of cake fertilizer and 300 kg/hm² of phosphate fertilizer are used as base fertilizer, with 450 kg/hm² of urea as top dressing for seedling and flower bell stages. Two top-dressing applications are made: the first in early June, and the second from late June to early July. For fields with poor fertility, such as wheat stubble, the fertilizer rate should be increased accordingly.
3.5.2 Garlic Cotton Intercropping
Garlic fields typically use 5000 kg/hm² of straw, 1500 kg/hm² of cake fertilizer, 1500 kg/hm² of phosphate fertilizer, and 75 kg/hm² of urea as base fertilizer. Three top-dressing applications are made, totaling about 750 kg/hm². For cotton intercropped with garlic, no additional base fertilizer is needed, and only 450 kg/hm² of urea is used as flower and bell fertilizer.
3.5.3 Watermelon Cotton Intercropping
Watermelon fields usually apply 1125 kg/hm² of cake fertilizer, 750 kg/hm² of phosphate fertilizer, and 112.5 kg/hm² of urea as base fertilizer. For cotton planted in these fields, 375 kg/hm² of urea is used as top dressing, divided into three light applications: 75 kg/hm² for seedlings, 225 kg/hm² for flowers and bolls, and 75 kg/hm² for the final top dressing.
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