Watermelon is the main fruit-based melon in the north of China. It has a large planting area and high yield. Scientific fertilization of watermelon can improve the utilization rate of fertilizer, achieve low consumption and high efficiency, maintain high quality and high efficiency characteristics of excellent varieties, fertilize soil and realize sustainable development of agriculture. In recent years, the quality of watermelon has a significant downward trend, and rational fertilization has a greater impact on the quality and yield of watermelon. The fertilization technology of Xiaolan watermelon in the northern greenhouse is introduced as follows.

1 Xiaolan watermelon needs fertilizer characteristics

According to the experimental observation, the absorption of nitrogen, phosphorus and potassium in Xiaolan watermelon is basically balanced with the growth of dry matter of the plant, that is, the amount of nitrogen, phosphorus and potassium absorbed in the early stage of growth and development is small, and it increases sharply after fruit setting. The absorption of nitrogen, phosphorus and potassium is the highest in potassium, followed by nitrogen and phosphorus. Generally, the ratio of nitrogen, phosphorus and potassium is 3:1:4.
The absorption of nutrients in different growth stages is: the absorption of nitrogen is very early, the growth of the vines is rapid, the absorption peak reaches the peak of absorption; the absorption of potassium is less in the early stage, and the absorption during the fruit expansion period rises sharply; the absorption of phosphorus The initial stage is higher, the peak appears earlier, the vine season tends to be stable, and the fruit expansion period is significantly reduced. There are two extremely important periods in the growth and development of watermelon, namely the critical period of nutrition and the maximum efficiency of nutrition. If these two periods can fully supply nutrients, the yield of watermelon will increase significantly.
For each 100kg of watermelon produced, about 0.19kg of nitrogen, 0.092kg of phosphorus, and 0.136kg of potassium are needed. In general, a sufficient amount of nitrogen fertilizer is the basis for high yield of watermelon; sufficient phosphate fertilizer is beneficial to hair roots, can promote plant growth and development, promote flower bud differentiation, make it flower early, sit early, mature early; potassium is more in plants An enzyme catalyst that promotes photosynthesis, protein synthesis, increased sugar content, and improved melon quality.

2 Determination of the amount of fertilizer applied

The application rate of nitrogen, phosphorus and potassium in production is generally N:P2O5:K2O=1:0.3～0.5:0.8～1, and the amount of fertilizer can be determined. It can be used for field trials to find reasonable dosage, and can also test the yield of the list. After the fertilization amount, soil fertility, fertilizer utilization and other relevant fertilization parameters, the soil nutrient content was determined before birth, and the fertilizer application amount was calculated by the nutrient balance method fertilizer application calculation formula. A summary analysis of the watermelon fertilizer test conducted in recent years in China, the field yield of watermelons with a yield of 37.5~45.0t/hm2 is generally N 300～345kg/hm2, P2O5 90～135kg/hm2, K2O 240～300kg. /hm2.

3 fertilization method

3.1 Apply sufficient base fertilizer
The base fertilizer of watermelon field is generally applied with organic fertilizer 15.0～22.5t/hm2, calcium magnesium phosphate fertilizer 600～750kg/hm2, urea 75kg/hm2, potassium chloride 120～150kg/hm2. It is advisable to apply the ditch, and it can also be applied to the melon and then turned into the soil.
(1) Add organic fertilizer. It is best to apply organic fertilizer with more cellulose (ie high carbon to nitrogen ratio), which can greatly enhance the nutrient buffering capacity of the soil, prevent salt accumulation and delay the soil salinization process.
(2) Deepen the ploughing of the soil. Since the salt accumulation in the soil of the protected area is condensed, after the vegetables are harvested, deep-turning is carried out, and the topsoil rich in salt is turned to the lower layer, and the lower layer of soil containing relatively less salt is turned over, which can greatly reduce the salt. harm.
(3) Deep application of base fertilizer. It is best to mix the fertilizer with the organic fertilizer on the ground and then plow it. Top dressing is generally difficult to apply in depth, so it is necessary to strictly control the amount of fertilizer applied each time. It is necessary to increase the number of top dressings to meet the demand for nutrients in watermelon. It is not possible to apply too much fertilizer at one time, resulting in an increase in the concentration of soil solution.
3.2 clever application of seedlings
At the seedling stage of watermelon, sufficient quick-acting fertilizer is needed in the soil to ensure the normal growth of the seedlings. In general, some of the fertilizers have been applied to the base fertilizer, as long as there is no symptoms of deficiency in the seedling stage, it is not possible to topdress. If the fertilizer applied in the base fertilizer is less, or the plot is not equipped with chemical fertilizer, the amount of seedling fertilizer should be chased in order to promote the normal growth and development of the seedling. The fertilization time is preferably when the seedling grows to 2 to 3 true leaves, or 60 to 75 kg/hm2 of urea is applied before the seedling water is poured. Seedling stage topdressing should not be too much, too close to the roots, so as not to cause dead roots.
3.3 foot chasing and spreading manure
After the watermelon melon has been stretched, it should be fertilized before the water is poured. Since the vines are covered with noodles soon after the vines are stretched, it is not advisable to carry out cultivating and fertilizing. Therefore, most of the fertilizer is applied at this time. Generally, the ternary compound fertilizer is 300-375kg/hm2, the urea is 300-375kg/hm2, and the potassium sulfate is 150-180kg/hm2. It is advisable to apply the ditch, but the ditch should not be too close to the melon plant to avoid damage to the roots and cover the soil after fertilization.
3.4 discretion to sit on the melon
Before and after flowering, watermelon is a key period for melons. In order to ensure that watermelon plants can sit on melons, they should not be topdressed. However, when the young melon grows to the size of the duck egg, the watermelon enters the peak of the absorption. In this period, if the lack of fertilizer not only affects the expansion of the melon, but also causes the later de-fertilization, the plant premature aging, which not only reduces the yield of watermelon, but also affects the quality of the melon. Therefore, it is necessary to use the high-concentration compound fertilizer 75-150kg/hm2 for water application.
3.5 late application of foliar fertilizer
After the watermelon is expanded, it enters the late maturity stage, and the ability of the root system to absorb fertilizer has been significantly weakened. In order to make up for the lack of roots, ensure the normal maturity of the watermelon and improve the quality, the leaf surface spray can be applied. For example, a 0.2% to 0.3% urea solution or a 0.2% urea + potassium dihydrogen phosphate mixed solution can be sprayed.

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