P Fractions in Soils and Their Availability in Chinese Fir-Plantations in South China

P fractions and their availability in soils of Chinese fir plantations in South China were studied. I-P(inorganic-P)was a major component of total-P and it accounted for 72.48% in lateritic soil, 73.20% in red soil, and 63.77% in yeillow red soil. Al-P, Fe-P, O-P, and Ca-P accounted for 2.74%, 4.70%, 84.74% and 7.81% in lateritic soil, 2.46%, 11.90%, 77.24%, and 7.81% of inorganic-P in red soil, 2.74%, 10.63%, 78.04% and 8.59% in yellow red soil, respectively. Organic-P in mountain yellow soil was a major composition of-P, and I-P only accounted for 30.56% of total-P. Al-P, Fe-P, O-P, and Ca-P in inorganic-P accounted for 1.54%, 15.67%, 78.85% and 3.94%, respectively. The distributions of Al-P, O-P, Fe-P and Ca-P in the four kinds of soils mentioned above had an obvious zonality and Al-P appeared the characteric of transitional soil, while those of O-P, Fe-P and Ca-P in the red soil region showed the complicated characteric and no homogeneity of-P fractions. The regression analysis indicated that there was a significant relationship between Fe-P and available P.