When is the best time to top-fertilize soybeans? How much fertilizer should be applied to one mu of land?

Soybean is a common economic crop in China, so it is planted in many areas, but if you want to grow soybean well, you need to do a good job in basic management such as water and fertilizer, light, temperature and so on. When will soybean be fertilized? How much fertilizer should be applied to one mu of land? How to fertilize?

1. The importance of topdressing soybean and the law of fertilizer requirement.

Topdressing is a kind of fertilizer applied to supplement the deficiency of base fertilizer according to the nutrient demand of crops during the period of crop growth. Topdressing is very important for the high yield of soybean. In order to meet the nutrient demand of growth and development in time, topdressing uses quick-acting fertilizers, such as chemical fertilizers and mature organic fertilizers. The methods of topdressing soybean fertilizer are spreading, furrow application, hole application, spraying and so on. The type, quantity, method and frequency of topdressing should be determined according to the weather, soil and soybean growth.

For every 100 kg soybean seeds, it is necessary to absorb 7.0kg / kg of nitrogen, 1.3kg / kg of phosphorus, 2.5kg / 4.0kg of potassium, and the ratio of nitrogen, phosphorus and potassium is 0.20.4. The nitrogen absorbed by soybean comes from nitrogen fixation of rhizobium of soybean itself, and the rest comes from soil and fertilizer. Phosphorus and potassium are mainly provided by soil. Soybean also needs boron and molybdenum, which is related to the nitrogen fixation ability of rhizobium.

The characteristics of fertilizer requirement of soybean at each growth stage are closely related to plant growth. The absorption of nitrogen by soybean accounts for 20% of the total absorption during the period from emergence to flowering, 55% from flowering to grain filling, and 25% from seed filling to maturity.

Soybean absorbs only 15% of the total phosphorus from emergence to early flowering stage; 60% from flowering to podding stage, reaching a peak; and 20% from podding to seed filling stage.

The absorption of potassium accounted for 32.2% of the total absorption of soybean from emergence to flowering stage, which was higher than that of nitrogen and phosphorus, and accounted for 61.9% from flowering stage to grain filling stage, while only 5.9% from filling stage to mature stage. The podding stage is the period when soybean absorbs the most nitrogen, phosphorus and potassium nutrients, and the absorption intensity is high, which is easy to lead to de-fertilization.

Second, how to fertilize soybeans?

In general, soybean enters the most vigorous growth stage from flowering stage, plant height, leaf area coefficient and dry matter accumulation are faster, and more nutrients are needed, but at this time, available nutrients in the soil usually drop to a low value and nutrient supply is inadequate. therefore, topdressing available nitrogen fertilizer in the early flowering stage of soybean can significantly increase dry matter accumulation and photosynthetic rate, which is an effective measure for high yield of soybean.

Topdressing nitrogen fertilizer should also be flexibly mastered according to plant growth and soil fertility, such as thin bean seedlings and barren soil, and topdressing time should be advanced in order to promote vegetative growth and build a high yield shelf. If the plot that has been fertilized at the seedling stage is still short of fertilizer at the flowering stage, it can be made up for once. If the bean seedlings grow healthily, the leaf area coefficient is too large, and the soil alkali-hydrolyzable nitrogen content is more than 80 mg / kg, there is no need to apply nitrogen fertilizer at the early flowering stage, so as to avoid excessive growth and lodging. With the topdressing of 10-15 kg urea per mu, the barren land and weak seedlings can be more suitable. Topdressing is best applied in ditches, and urea can also be sprinkled between rows, preferably in combination with ploughing and irrigation to ensure fertilizer efficiency. Application should avoid sprinkling fertilizer on the leaves to prevent burns.

Phosphate fertilizer is generally used as base fertilizer. If there is phosphorus deficiency, it can be ditched and applied phosphate fertilizer in soybean seedling stage or early flowering stage. If there is a serious lack of phosphorus, it is still necessary to topdressing phosphate fertilizer at podding stage. The amount of topdressing fertilizer is generally about 25 kg per mu of calcium superphosphate or other equivalent amount of available phosphate fertilizer, and can be applied more appropriately when there is a serious phosphorus deficiency. Soybeans have less phosphorus topdressing after podding period. Because the movement of phosphorus in the soil is very small, it must be applied in the plough layer, preferably in the furrow; in the soybean grain filling stage, it is best to spray outside the root.

Potassium fertilizer should be applied early, and it is best to topdressing soybean seedlings to the early flowering stage, applying 7.5-10 kg potassium sulfate per mu or the same amount of other available potassium fertilizer to the plough layer.

The topdressing of soybean can be combined with watering, ploughing and soil cultivation. The farming gang suggests ploughing and cultivating the soil immediately after topdressing to avoid fertilizer loss.

Third, how to fertilize soybeans?

Foliar spraying is a method of topdressing outside the roots of plants, usually spraying fertilizer solution or dry powder on the leaves or backs of crops with a sprayer. Foliar spraying can absorb fertilizer directly through leaves, and quickly transport it to various organs, participate in the biochemical process in vivo, and significantly increase yield and improve quality. Because this way does not pass through the soil, nutrients will not be fixed by the soil, and the fertilizer efficiency is high. But this is only a way of extra-root topdressing, not a substitute for root topdressing.

The fertilizers commonly used for foliar spraying of soybeans are urea, potassium dihydrogen phosphate, etc., and the concentration of spraying is 1%-2%; the concentration of trace elements boron, manganese, copper and zinc salts is generally 0.1%, and the concentration of molybdate is 0.01%-0.05%.

The proportion of spraying topdressing on soybean leaves is generally 0.5 kg of urea, 0.5 kg of potassium dihydrogen phosphate or 1.5 kg of superphosphate, 0.75 kg of potassium sulfate, 50 kg of water, sprayed on plant leaves. Soybean foliar spraying should be carried out after 4 p. M. on cloudy or sunny days. The absorption and utilization rate of spraying on the back of plant leaves was higher than that on the front. Generally, it can be absorbed and utilized by soybean plants 2-8 hours after spraying.