Nitrogen deficiency
Watermelon is sensitive to nitrogen. Generally, the average amount of nitrogen absorbed per mu is about 11 kg. Lack of nitrogen, slow growth of plants, weak stems and leaves, chlorosis and yellowing of lower leaves, shortened internodes of new shoots of vines, slow expansion of young melons, small fruits and poor quality. On the basis of general application and high-yield furrow application of organic fertilizer, topdressing urea should be applied in stages, in which about 10 kilograms of seedling fertilizer per mu is applied; 10-12 kilograms of vine fertilizer; and 15-20 kilograms of resultant fertilizer. It is also possible to topdress 500 to 600 kg of human excrement per mu. At the same time, foliar topdressing is carried out as appropriate, with 0.3% urea in the seedling stage and 0.5% in the fruit-bearing stage.
Phosphorus deficiency
Phosphorus can promote the growth of watermelon root system and enhance the ability of root system to absorb water and fertilizer, especially in the low temperature season, the effect of phosphate fertilizer is more obvious. Watermelon requires less phosphorus than nitrogen, with an average absorption of about 3.5 kg of phosphorus per mu. But lack of phosphorus, poor root system development. The plants are small, the back of the leaves are purple, the flower buds are poorly differentiated, the flowering is late, the fruit setting rate is low, and the flowers are easy to fall and "melon". And yellow fibers and hard lumps often appear in the pulp, the sweetness is decreased, and the seeds are not full. You can apply 15-30 kilograms of superphosphate per mu in the furrow; you can also mix the superphosphate with organic fertilizer and sprinkle it into the melon furrow to effectively prevent phosphorus deficiency. If symptoms of phosphorus deficiency are found, 0.4% to 0.5% superphosphate extract should be sprayed on the leaf surface in time.
Potassium deficiency
The potassium absorption of watermelon is the highest, which is 1.2 times and 3.4 times that of nitrogen and phosphorus, respectively. Due to potassium deficiency, the resistance of plants is reduced. The transport organization is not smooth, nutrient synthesis and transportation are blocked, so the sugar accumulation in the fruit is insufficient, which reduces the yield and quality of watermelon. It is characterized by slow plant growth, weak stems, shrinkage of the leaf surface, brown and dead edges of old leaves, and gradually expand inward. In severe cases, it develops to the center of the leaf, the leaf color is light green, and the leaf edge is scorched. The fruit expands slowly, the melon is small, it is difficult to set the fruit, and the room for fixing the melon is small. Moreover, the fruit has low sugar content, large sugar gradient and poor quality. Pay attention to the use of potash fertilizer in production. Firstly, apply 60-100 kg of plant ash per mu in furrow, secondly, apply about 5 kg of potassium sulfate per mu during the seedling stage; apply 8-10 kg of potassium sulfate per mu after vine extraction to before fruit setting; spray after fruit setting to fruit swelling period Foliar fertilizer is powerful potassium, once every 7 to 10 days.
Calcium deficiency
Calcium deficiency in watermelon mostly occurs in plots where calcium-free fertilizers have been applied for many years. When watermelon lacks calcium, the top leaves turn yellow and the lower part remains green. This is a typical feature of calcium deficiency and nitrogen, phosphorus, and potassium deficiency. In addition, watermelon calcium deficiency is accompanied by yellowing of the leaf margins, the leaves curl outwards and are parachute-shaped, the top part of the plant becomes brown and necrotic, and the stems stop growing. Due to insufficient calcium intake in the ovary when the flower buds differentiate, it often causes fruit malformations. The remedial measures are: 50-100 kg of superphosphate per acre of furrow; mulch ridge mulch, grass in the border, moisture preservation, prevention of drought, and promotion of calcium absorption; combined with soil fertilization, use Weili calcium foliar spray to supplement the root system Insufficient absorption of fertilizer.
Boron deficiency
Watermelon absorbs more boron than crops, and is prone to boron deficiency in soils with less organic fertilizer and no boron fertilizer. In addition, sandy loam and alkaline soils are easy to reduce the availability of boron and lead to boron deficiency in plants. When watermelon lacks boron, the new leaves do not stretch, the leaf surface is uneven, and the leaf color is uneven; the internodes of the new vines become shorter, the vine tips stand upright, and the new vines have horizontal cracks, which are brittle and easy to break. The section is brown, and when it is severe, the growth point will die and stop growing. Sometimes a reddish-brown paste is secreted on the vine shoots; the lack of boron in watermelon often causes the flowers to develop incompletely, and the fruit is deformed or cannot produce normal fruit. Generally, start to spray Weili Boron 4 to 5 times in the bud stage, once every 7 days, the effect is better.
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