(1) Nutritional characteristics of the root system: The root system of watermelon is strong and widely distributed. The main root depth is more than 1 meter, and the lateral roots extend 4 to 6 meters. The distribution of major root groups depends on soil conditions, especially soil moisture conditions. The main root groups of dry melons are mostly distributed in the range of 50-60 cm with a horizontal radius of 1.5 m. The watering fields are distributed in 30-40 cm with a lateral radius of 1 m. Watermelon roots are not tolerant to wetness and weak in regeneration. Therefore, they are generally used for direct seeding or container breeding. Watermelon has a wide adaptability to soil, and has strong water-absorption and fertilizer-absorption capacity, but it has obvious aerobicity because of its root system. Therefore, it is best to choose fertile sandy loam or loam, the top layer of soil is sand, the bottom layer is loam, and the best place for planting watermelon is the plot of pH 6.8~7.0. Clay watermelon should be re-applied organic fertilizer to improve its permeability.
(2) Fertility dynamics of watermelon: The growth period of watermelon is longer and the amount of fertilizer required is larger. During the whole growth period, the amount of potassium uptake was the most, followed by nitrogen and phosphorus. The amount of nitrogen, phosphorus, and potassium absorbed by watermelon plants at each growth stage is basically the same as the change in dry matter growth. The absorption of watermelon seedlings is very small, accounting for only 0.54% of total absorption. With the rapid growth of stems and leaves, the absorption of vines increased, accounting for 14.66%. Although the melon period was short, the absorption amount was 7.04%, and the average daily absorption was larger than the previous period. The largest amount of fertilizer was absorbed during the expansion period, accounting for 77.74% of the total period. The average daily absorption was the highest during this period. During the mature period, due to the gradual decline of the leaves and the decrease of the content of three elements in the organs, the total amount of the three elements of the plants decreased, the absorption amount was negative, and the law of the fertilizer requirement was “Sâ€.
In different periods, the proportions of the three elements absorbed by plants were also different. Before the end of the melon period that formed the nutrient system, the plants absorbed the most nitrogen, followed by potassium; while in the expansion stage and the mature period, the plants absorbed the most potassium, and nitrogen The. Therefore, the main nitrogen-based flowering and sitting on melon, pay attention to the application of phosphorus and potassium fertilizer during the expansion period is particularly important to increase production and improve quality.
According to the test, for every 1,000 kilograms of watermelon products produced, 2.25 kilograms of nitrogen, 0.9 kilograms of phosphorus, and 3.38 kilograms of phosphorus are required. The ratio of three elements is 3:1:4. The sensitivity to boron, zinc, molybdenum, manganese, cobalt and other trace elements. There are also certain requirements for calcium, magnesium, iron and copper.
In each nutrient element, potassium can significantly increase production and improve quality. While satisfying nitrogen and phosphorus nutrition, potassium is applied at a rate of 300-375 kilograms per hectare, the quality of the watermelon is good, the yield is high, and the benefit is good. With the increase of the amount of potash fertilizer, the plant's ability to resist virus disease, blight, and anthracnose increased significantly. Potassium has a good coordination effect on leaf nitrogen metabolism. Phosphorus fertilizer can increase the chlorophyll content and photosynthetic intensity, promote root flow and phosphorus content, increase the activity of sucrose phosphate synthase, and contribute to the accumulation of sucrose in fruits. Watermelon is a bogey chlorine crop, so do not apply fertilizers such as potassium chloride and ammonium chloride that contain Cl-, otherwise it will reduce the quality.
The absorption of each element of watermelon has the most suitable peak, and the interaction between any two elements is positive. It shows that in the cultivation of watermelon, in order to have high quality, high yield, and high efficiency, it is necessary to do a reasonable combination of organic fertilizer and inorganic fertilizer, and a reasonable ratio of three elements and other elements.
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