What is the application ratio of special fertilizer for cotton drip-irrigated fields?
I. Total fertilizer application for cotton
In high-latitude marginally suitable cotton areas, for a seed cotton yield of 300-380 kg, 70-80 kg of natural fertilizer is needed, equivalent to 160-180 kg of standard fertilizer. This achieves "a jin of fertilizer for a jin of cotton." Applying 1 kg of standard fertilizer can produce 1 kg of lint cotton. Soil test results and cotton plant nutrient diagnosis in Regiment 137 generally show zinc deficiency; applying 1-2 kg of zinc fertilizer in autumn increases yield by 5%-10%. For plots with abundant potassium according to test results, potassium fertilizer application is 5-10 kg, especially for plots with potassium content below 180-280 mg/kg, which can still increase yield by 5%-8%. Boron fertilizer (Sulubor) can be sprayed on the leaves at the full bud stage to early flowering stage. Organic fertilizer is applied to the full layer at 1-2 tons per 667 sq m in autumn and winter. Cotton yield and chemical fertilizer application are proportional within an effective range. Applying 100-120 standard fertilizer units produces 250-280 kg of seed cotton.
II. Base-to-topdressing ratio of cotton special fertilizer
Cotton needs to absorb nutrients throughout its entire growth and development period, with the largest absorption during the flowering and boll stage. In drip-irrigated cotton fields, cotton roots are relatively shallow, and with deep autumn plowing by high-horsepower machinery, autumn fertilization depth is 30 cm, while in the early stage cotton roots are mainly at 10-20 cm. Therefore, 30%-40% of nitrogen fertilizer and 80%-90% of phosphorus, potassium, and zinc fertilizers can be applied to the cotton field in autumn during full-layer application of organic fertilizer, while 60%-70% of nitrogen fertilizer and 10%-20% of phosphorus and potassium fertilizers can be applied with drip irrigation during the cotton growth period. For foliar fertilization, use urea plus nitrogen-added potassium dihydrogen phosphate or drip-irrigation special fertilizer. For a small number of furrow-irrigated cotton fields, 60%-80% of nitrogen fertilizer and 10%-20% of phosphorus and potassium fertilizers can still be applied to the cotton field in autumn during full-layer application of organic fertilizer, while 20%-40% of nitrogen fertilizer and 10% of phosphorus and potassium fertilizers can be applied to the cotton field during irrigation, combining irrigation with "one irrigation, one fertilization."
If the base-to-topdressing ratio of cotton is unreasonable, with a large base fertilizer proportion, cotton seedlings and buds tend to grow excessively, and nutrient deficiency in the middle and late stages leads to premature senescence. Insufficient phosphorus and potassium fertilizer during the flowering and boll stage causes bud and boll shedding, reddening and chlorosis of leaves, and decreased boll weight, resulting in reduced yield. Therefore, supplementing potassium fertilizer during the cotton growth period is an effective way to increase yield.
III. Nitrogen, phosphorus, and potassium ratio of autumn-applied special fertilizer
According to the fertilizer requirements and application methods of cotton in drip-irrigated cotton fields, the ratio of pure nitrogen, phosphorus pentoxide, and potassium oxide in autumn-applied special fertilizer should be 12-18:27-28:5-9. The effective total nutrient content should be greater than or equal to 45%. According to the target cotton yield and soil test results, apply 20-25 kg per 667 sq m in autumn. For a small number of furrow-irrigated cotton fields, the ratio of pure nitrogen, phosphorus pentoxide, and potassium oxide in autumn-applied special fertilizer should be 20-22:17-18:4-9. The effective total nutrient content should be greater than or equal to 43%. Zinc and boron fertilizers each account for 1%-2%. The total autumn-applied special fertilizer usage is 35-40 kg per 667 sq m. The original autumn-applied special fertilizer formula (nitrogen, phosphorus, potassium ratio of 22:18:4) had relatively low phosphorus and potassium content and only satisfied the autumn application needs of a small number of furrow-irrigated cotton fields. Regiment 137 proposed the formula fertilizer principle of "reduce nitrogen, stabilize phosphorus, increase potassium" for autumn-applied special fertilizer.
If the nitrogen, phosphorus, and potassium ratio of autumn-applied special fertilizer is unreasonable, it not only increases the cost per 667 sq m but also reduces fertilizer use efficiency, making it easy for workers to be unwilling to apply it and to not use special fertilizer.
IV. Nitrogen, phosphorus, and potassium ratio of drip-irrigation special fertilizer
According to the fertilizer requirements and application methods of cotton in drip-irrigated cotton fields, the ratio of pure nitrogen, phosphorus pentoxide, and potassium oxide in drip-irrigation special fertilizer should be 9-12:2-12:42-44. The effective total nutrient content should be greater than or equal to 58%. According to cotton growth conditions and soil nutrient supply capacity, it can be applied with drip irrigation during the watering period. In addition to urea, the commonly used drip-irrigation fertilizer in Regiment 137 can include nitrogen-added potassium dihydrogen phosphate (nitrogen, phosphorus, potassium ratio of 6:12:42). This product is very similar to the Israeli drip-irrigation fertilizer product "Potassium Treasure" (nitrogen, phosphorus, potassium ratio of 12:2:44) and has very good application results.
If drip-irrigation fertilizer is mainly urea and no attention is paid to the rational combination of fertilizers and nutrient elements, with excessive nitrogen fertilizer and relatively high cotton density, vegetative growth becomes excessive, the population grows too vigorously, the field becomes shaded and closed, and cotton plants become hollow, stay green and mature late, and fail to form economic yield.