In the past, when low-strength phosphorus general-purpose calcium phosphate was used, there was no problem of sulfur deficiency in soil. However, in recent years, after replacing high-density heavy calcium phosphate, soil sulfur deficiency occurred in some areas. Why is this? To clarify this issue, we must start with the composition of calcium phosphate and heavy superphosphate.
The main component of calcium phosphate is phosphorus monocalcium phosphate, which contains 14% to 18% of phosphorus, and calcium sulfate, which accounts for about 50%. Therefore, the application of universal calcium phosphate can not only provide phosphorus nutrition to crops, but also enable crops to obtain sulfur nutrition. However, superphosphate has a low phosphorus content and contains a large amount of accessory components. In order to overcome this shortcoming, there has been a type of phosphate fertilizer that is heavy calcium phosphate.
The heavy calcium phosphate is improved in the manufacturing method, so that impurities such as calcium sulfate are not contained in the fertilizer, so that the content of phosphorus is greatly increased and becomes a high-concentration phosphate fertilizer. Therefore, the problem of sulfur deficiency naturally occurs when heavy superphosphate is applied year-round.
The symptoms of crop sulfur deficiency are very similar to those of nitrogen deficiency. The main feature is the chlorotic chlorosis of leaves, but from the subtle manifestations, they are different. The symptoms of nitrogen deficiency begin with the lower old leaf, and the symptoms of sulfur deficiency start from the upper new leaf. For example, in the case of sulfur deficiency in potatoes, the upper leaves are generally yellowed, and when they are severe, brown spots appear on the leaves.
Therefore, when planting sulfur-loving crops, it is recommended that calcium phosphate be used or calcium phosphate and calcium superphosphate be used alternately, so that the problem of sulfur deficiency can be alleviated by applying high-concentration phosphate fertilizers all year round.
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