Studies On Transformation And Availability Of Different Phosphates In Crop Rhizosphere In Calcareous Chao Soils

The transformation, availability of phosphates in the crop rhizosphere and the biological properties of the rhizosphere after application of different phosphates in calcareous Chao soils were studied by methods of pot trials and indoor analysis. The results gained are as follows:1. In the tested calcareous soils, the activities of phosphatases were enhanced with the crop growth after the application of various forms of phosphates. The activities of the phosphatases were generally in the order of Ca,0-P > SSP > K2HPO4 > CaMg-P > CK. The activity of alkaline phosphatase was higher than of neutral phosphatase. The alkaline phosphatase activity in light clayey soil is higher than that in light loamy soil, also is higher in poor-phosphate soil than in rich-phosphate soil.2. In the growing period of crops, there was evident difference on the transformation of phosphates between rhizosphere soil and bulk soil among the various treatments. K2HPO4 mainly changed into Ca2-P, Ca8-P, Al-P and Ca10-P, and SSP not only changed to Ca2-P, Ca8-P and Al-P, but also promoted Ca10-P to available; CaMg-P mainly transformed to Ca2-P and Ca8-P, while CalO-P mainly existed in its own original form in the soil with very low availability.3. There were significant positive correlation between the amount of fast available phosphorus and those of Ca2-P and Fe-P during tillering stages of wheat, and those Ca2-P, Ca8-P and Fe-P during jointing stage, Fe-P in grain-filling stage , also Ca2-P Ca8-P and Fe-P in mature stage of wheat. While in negative relation to Ca10-P and O-P in soils. This means that Ca2-P, Ca8-P, Al-P and Fe-P are important to increase soil availablephosphorus.4. In the two tested soils, the amounts of organic phosphorus (or-P) was in the sequence of middle active or-P ?active or-P > middle stable or-P > high stable or-P. The various phosphates applied in soils all could raise the amount of or-P, and mainly increase the middle active or-P and active or-P, especially after use of K2HPO4. The amounts of the four kinds of or-P in light loamy soil were all higher than in light clayey soil. Compared with bulk soil, the total or-P and its four components, available P all showed deficiencies in rhizosphere soil, especially in treatment of K2HPO4 The middle active or-P and active or-P were liable to be mineralized and more available to crops.5. The numbers of micro-organisms in rhizosphere and in bulk soil and its rhizosphere effects varied significantly among the treatments, with the order of K2HPO4 > CaMg-P > SSP > CalO-P > CK. With the growth of crops, the rhizosphere microorganisms increased gradually and came to peak.6. Seed-soaking with ABT rooting powder could stimulate the wheat root growth and promote a higher use efficiency of soil phosphate. The P use efficiency and P supplying power varied among soils with different phosphate levels. Rich-P soils had a lower P use efficiency.