Nitrogen and potassium balanced fertilization of sweet potato can yield high yield
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From the nutrient absorption law of sweet potato at each growth stage, the absorption of potassium was the most in the whole process, and the most obvious expansion of potato tubers. As the roots expand, the amount of potassium absorbed increases simultaneously. Some varieties also showed that the potassium content of the large potato pieces was higher than that of the small potato pieces. The absorption characteristics of nitrogen in sweet potato are more in the long period of stem and leaf, and gradually decrease in the later stage of growth. For the absorption characteristics of phosphorus, the phosphorus content in different stages is lower, and the phosphorus content in seedling stage is the highest. The supply level of nitrogen is important for the growth stage of sweet potato in the early stage, the plant reaction is also sensitive, and the growth of nitrogen-deficient shoots is slow. However, if the nitrogen is applied too much, the leaf area index is too high, and the upper leaves are shielded from the lower leaves, which will not increase the yield but will reduce the yield. A large number of field trials have shown that high nitrogen supply will increase the proportion of stems and leaves, while low nitrogen treatment will increase the weight gain of potato tubers and the number of potatoes. On the basis of appropriate nitrogen supply, potassium nutrition can prolong the functional period of the leaves, strengthen the formation of potato chips and promote its expansion, because the balance of nitrogen and potassium accelerates the transportation of photosynthetic products to the roots, and promotes the synthesis and accumulation of starch. . According to the US Science and Technology Experiment, the potassium content of sweet potato leaves is less than 0.5%, that is, the symptoms of potassium deficiency occur. Only when it is kept at about 2% is it beneficial for healthy growth. In the field, such as sweet potato leaves dark green and brown necrotic spots on the back of the leaves, it may indicate potassium deficiency.
Whether the balance between nitrogen and potassium affects the yield level of sweet potato; under the condition of increasing nitrogen fertilizer, the corresponding increase of potassium fertilizer can inhibit the madness of shoots and leaves in the shoots; increase the distribution rate of photosynthetic products to roots. If the relationship between nitrogen and potassium is simply referred to as potassium and nitrogen ratio (K2O/N). Then, the potassium and nitrogen ratio (K2O/N) of high-yield fields are generally higher than 2. For example, if there is too much nitrogen supply, it often forms a “crazy long†in the upper part of the earth, also called “running the scorpionâ€. However, the amount of nitrogen used is too low, because less nitrogen does not guarantee sufficient vegetative and assimilation rates. In terms of the dry matter distribution rate of sweet potato, the effects of potassium and nitrogen in leaves are also different. Potassium-containing high dry matter is mainly distributed in the underground, and nitrogen-containing high dry matter is mainly distributed in the ground. In order to obtain a reasonable root-to-root ratio (ie, root to plant weight ratio), nitrogen and potassium fertilizers must be adjusted and rationally applied. At present, the common situation in production is that the ratio of potassium to nitrogen in the plant is low, and the application of potassium fertilizer should be beneficial to create high yield of sweet potato. Balance fertilization, but also master the correct fertilization method. The base fertilizer of sweet potato is best applied in the soil layer of 10-30 cm, which is beneficial to root absorption, especially the solubility and diffusion of phosphate fertilizer is slow. It is also necessary to combine deep application with shallow application, and layered and staged fertilization can meet the requirements of the former. The need for nutrients in the later period can avoid the problems of early premature aging and early premature aging. In the early stage of topdressing of sweet potato, the application of nitrogen fertilizer was the main; the quick-acting nitrogen fertilizer was used, and the potassium fertilizer was mainly applied in the later stage. The strong fertilizer in the early stage, about 5 kg per mu, to promote the growth of sweet potato stems and leaves. In the medium-term long-term potato fertilizer, when the roots begin to expand, the long-term potato fertilizer should be re-applied, and the amount of fertilizer applied accounts for most of the total topdressing amount, mainly nitrogen and potassium. Generally, about 10 kg of nitrogen is applied per mu, and 10 to 15 kg of potassium sulfate is applied.
In addition, in the land with good water and fertilizer conditions, the topdressing is too early or too much, which may cause the medium-term growth to be too strong, hindering the movement of nutrients to the roots, but will delay the potato. Under the general fertility conditions, the strong potato fertilizer can be properly early, the late dressing is easy to cause stems and leaves, and the potato blocks do not gain weight.
(Senior Consultant of Sinofert, Professor of China Agricultural University Cao Yiping)