Phosphorus Fraction And Variation Characteristics And Their Influencing Factors Analysis On Calcareous Purple Soil Under The Rotation System Of Different Crops

The phosphorus(P) content of the calcareous purple soil under two typical rotation systems of the arid land in the central hill region of Sichuan basin was studied,by the method of located monitoring. And the phosphorus fraction and variation characteristics and their influencing factors were also studied, taking the method of inorganic phosphorus(Pi) fractionation in calcareous soil from Jiang Bofan and Gu Yichu.The results indicated that:(1) The average total phosphorus content(TP) in surface soil under the two types of rotation systems were 0.75 and 0.54 g kg^-1,which were on the middle level.And each the Olsen-P content were 3.3 and 1.4 mg kg^-1,which were on the low level.Certain characteristic of P lack was found in the growth stages of rape,wheat and corn during the research.For the results,the soil studied was not surplus of P,but need to test the soil P content of the crop to apply P fertilizer.The TP and Olsen-P content were higher in surface soil than subsurface soil.The TP of the studied soil was mainly made up of Pi,and it stood 88%of the TP content in surface soil,even 91%in the subsurface soil.The organic phosphorus(Po) percentage was higher in surface soil than that in subsurface soil,on the ground that the Po had significant revelation with soil organic matter(OM),and the OM content in the surface soil was higher than that in the subsurface soil.(2) The total characteristic of Pi fractionations under the two types of rotation systems showed that: Ca₁₀-P content took the most part of the total Pi content.It stood 67%and 74%of the total Pi content in the surface and subsurface soil.Ca₈-P and O-P content took the 2^nd and 3^rd place in the surface soil and on the opposition in the subsurface soil.Al-P,Fe-P and Ca₂-P took the 4^th,5^th and 6^th place both in the surface and subsurface soil.The percentage of Ca₂-P content was very low,taking less than 1%.This main trend kept steadly though the Pi fraction form and content changed during the different growth stages and among the three crops under the two types of rotation systems.The results of multiple regression analysis indicated that the soil Olsen-P was mainly from Ca₂-P which was one of the Pi fractions,and it had no relations with other forms of Pi.So,the Ca₂-P content was low in the studied soil.It was the basically reason which led to the low content of Olsen-P.(3) The characteristics of soil Pi fraction variation were much complex in the growth stages of corn, rape and wheat.They were different with each other in different crops,and so were the characteristics of different Pi fraction variation in the same crop.(4) The Pi fraction and variation were mainly influenced by microtopography,rotation,soil organic matter and soil granule composition,and had no relation to soil pH.Microtopography mainly affected the Ca₁₀-P content of the subsurface soil.The difference of it reached to extremely significant level among the subsurface soils under each rotation system,and each the "t" value of the difference under the rotation was t=3.486^**(P=0.004,n=16) and t=4.242^** (P=0.001,n=16).Rotation showed heavy influence to Ca₈-P,but showed not enough significant influence to other types of Pi.Ca₈-P content showed extremely significant difference(t=-3.025^**,P=0.004,n=40) in surface soil under different rotation systems,and it showed significant difference(t=-2.562^*,P=0.018, n=32) in subsurface soil.The content of each type of Pi showed no correlation with soil pH,the correlation didn't reach to significant level.It's on the ground that the changing range of the soil pH value was very narrow.Among the Pi fractions,Ca₈-P and Al-P content were positively correlated with soil OM,and the correlation coefficient were(r=0.267^*,n=72) and(r=0.295^*,n=72).The content of other types of Pi showed no correlation with soil OM,the correlation didn't reach to significant level.Among the soil granule composition,only silt showed influence to Ca₈-P and Al-P,and the Ca₈-P showed significant correlation with silt(r=0.264^*,n=72),the Al-P showed significant correlation with silt(r=0.301^*,n=72).