AN INTRODUCTION ON THE MAP OF POTENTIAL OF PHOSPHATE NUTRITION IN THE SOILS OF CHINA
Jiang Bo-fan, Lu Ru-kun and Li Qin-kui (Nanjing Institute of Soil Science, Academia Sinica)
The present map shows the general status of the potential of soil phosphate nutrition of China, including the content and composition of soil phosphorus and crop respouse to different phosphatic fertilizers. Besides, the phosphorite deposits suitable for the direct application in the form of powdered rook phosphate are marked on the map. It is found that the compositions of different forms of soil phosphorus are most closely related with the zonality of main soil groups. Six types of the potential of phosphate nutrition are classified according to the composition of soil phosphorus. In the forest soils and meadow soils about 50—80 per cent of total phosphorus are presented in organic form. In large areas of the pedocal regions of China, soil phosphates mainly remain in forms of fluor-apatite and hydroxyl-apatite, and rich in total phosphorus, but their availability sometimes are low. In lateritic soils, red soils and yellow soils of southern China, these primary phosphate minerals have been highly weathered, and iron phosphates admixed with a very small amount of aluminium phosphates become the principle type of soil phosphate. However, the iron and aluminium phosphates in these soils are mostly coated by a film of colloidal iron oxide and formed occluded phosphate, which can be only liberated under strongly reduced soil condition. Crystalline iron phosphate which has been proved unavailable to upland crops, however even in the form of strengite, shows high activity in paddy soils as in the case of amorphous iron phosphate. Calcium, iron and aluminium phosphates all have been found in brown soils, drab soils and other soil types in the transitional zone, all of which range in pH 6.5—7.5, in general the soil phosphates is more available. It could be concluded that according to the composition and content of soil phosphate and crop response to phosphatic fertilizers, the potential of phosphorus nutrition of soils are obviously increased in order from the south to the north of China. The following legend is attached to this map.