Second, the theoretical basis for soil testing and formulating Fertilization Formulated fertilization, taking into account the crop, soil, fertilizer system interrelated, its theoretical basis is mainly the following aspects. (a) The crop yield increase curve confirms the existence of a law of diminishing returns to fertilizers. Therefore, the fertilizer input to a certain crop species should have a certain limit. In the low- and medium-fertilized regions, the rate of increase in fertilizer application is large, while in high-yielding regions, the technical requirements for the application of fertilizers are relatively strict. Excessive input of fertilizer, no matter what kind of area, will lead to a decline in fertilizer efficiency, resulting in reduced production. Therefore, determining the most economical fertilizer use is the core of formula fertilization. (b) A certain proportion of the various nutrients necessary for crop growth. Targetedly addressing the minimum nutrients that limit the increase in local production, coordinate the proportional relationship among various nutrient elements, correct the prejudice of past single fertilization, and apply the combined application of nitrogen, phosphorus, potassium, and trace element fertilizers to exert the nutrients. Promoting each other's functions is an important basis for formula fertilization. (3) Under the guidance of the principle of nutrient restitution (compensation), formula fertilization embodies the contradiction between the need of crop fertilizer and soil fertilizer supply. The growth of crops not only consumes soil nutrients, but also consumes organic matter of the soil. Therefore, the correct handling of the relationship between fertilizer (organic and inorganic fertilizer) input and crop yield, land use and land use is an important measure to increase crop yield and improve quality, as well as maintain and increase soil fertility. (4) Soil testing and formula fertilization is a comprehensive technical system. Although it determines the total amount of fertilization for different nutrients as the main content, in order to give full play to the maximum yield-increasing effect of fertilizers, fertilization must be combined with various factors affecting fertility, such as selection of improved varieties, fertilizer and water management and farming systems, and climate change, and formula fertilizer production requirements. There is a strict organization and serialized service to form a complete set of fertilization technology system.
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