The reserve of soil nutrients is limited.In case of irrational use of land,nutrients would be depleted sooner.Before the 1950s the low grain production in China was maintained only by expanding the cultivated area and by recycling of nutrients in agriculture.Calculation of nutrients balance showed that in the year of 1949 there were great deficits of N,P and K elements in agriculture of China.It revealed that there would have really been danger of soil nutrients exhaustion if such a situation had continued.Things have changed since the beginning of 1950s.The nutrients balance in agriculture has been getting better and better.In the year 1987 N and P balance got rid of their great deficits.But for K and deficit grew even larger.This resulted in a rapid expansion of soil area deficient in K in China since the mid 1970s.In spite of the fact that the P balance in the arable land of the whole country was positive,the field which did not receive P fertilizer had become deficient in P.So the area deficient in P also increased.It is stressed that great attention should be paid to the depletion of soil nutrients,especially K in the northern part of China where the soil is relatively rich in K.Of course,soil sulfur and microelements should be considered next.
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