Studies On Variation Of Phosphorus Fractions In Calcareous Soils With Different Fertilities

Based on the two fertility indices, organic matter and total nitrogen, 73 typical soil samples collected from calcareous cultivated soils with different yield levels in 10 counties of Henan Province were divided into three categories in fertility by hierarchical clustering analysis. Then by methods of fractionation of inorganic and organic P in soils and multivariate statistical analysis, this paper discussed phosphorus fractions in soils with three fertility levels and in different soil layers. The affecting factors on fast-available P (Avail. P) were also related. The results are as follows:1. There were significant differences among the amounts of soil P and its fractions of inorganic P (Pi) and organic P (Po) at three fertility levels. The total P increased with the raising of soil fertilities. Total P in soils mainly occurred in the form of Pi, which made up 86.40% of the total, while the proportion of Po only accounted for 9.41%. The variation of Pi was little in the soils with three fertilities. And the proportion of Pi in total P decreased while the proportion of Po went up with the increase of soil fertility. That is to say, there was enrichment tendency for phosphorus, especially for Po, with the increase of soil fertility.Pi mainly occurred in Ca-P forms in which Ca10-P made up most in 58%~61%, while the amount of Ca2-P was very lower. Po exists mainly in the form of mid-labile Po (around 66%~69%). The amounts of Ca2-P, Al-P, labile Po and mid-labile Po, which are more available for plant, increased with the improvement of soil fertility,but generally the avail. P was very poor in soils.2. The activity of phosphatase in soils went up with the increase of fertility levels and lowered with the deepening of soil layers. Either neutral phosphatase or alkaline phosphatase had significant positive relations to soil O.M, Po and avail. P. The activity of neutral phosphatase was stronger than the alkaline phosphatase in the tested calcareous soils.3. There were close relations between soil avail. P and the three indices, total P, O.M and mineral particles of 0.02~0.002mm in diameter, according to correlation analysis, path analysis and stepwise regression. The correlations between avail. P to Ca2-P, Al-P, labile Po and mid-labile Po in soils were significant. Partial correlation also showed there was closer relation for avail. P to Po than that to Pi in tested soils.4. The avail. P, total P, fractions of Pi and Po in 0~20cm soil layers were higher than those in 20~40cm soil layers. The percentages of soil samples(0~20cm), in which the avail. P were divided into 4 grades, i.e. >18 mg.kg-1, 10-18 mg.kg-1, 5-10 mg.kg-1 and <5 mg.kg-1, accounted for 9.6%, 30.1%, 35.6% and 24.7% of total soil samples, respectively.The phosphorus activation coefficient (PAC) was generally lower in different soil layers and at different fertility levels in calcareous soils. PAC increased correspondingly with the increase of soil fertility while PAC decreased with the increase of soil depth.