A STUDY ON DETERMINATION OF TOTAL AMOUNT OF AVAILABLE PHOSPHORUS IN SOILS
Chen Guomeng (Science and Technology Commission of Wenzhou City, Wenzhou, 325005) Lu Rukun (Institute of Soil Science, Academia Sinica, Nanjing, 210008)
Relationships between common methods of measuring soil available phosphorus and the actual total amount of available phosphorus (TAP) in soils were studied. TAP was obtained by planting crops successively until the crop was very insufficient in P. Olsen-P (P_ol) was estimated at only 17% of TAP, and anion exchange resin P (P_ar) at about 42% of TAP. EDTA+NaHCO_3-P(P_e) and ATR mixed CER-P(P_mr) were poorly correlated with TAP. Cowell total (P(P_ct) was approximately equal to TAP. The correlation coefficient between Cowell total P and TAP was 0.825, significant at 0.001 level. The correlative coefficient between Cowtll inorganic P(P_ci) and TAP was 0.772, significant at 0.01 level. The content of organic P which is available for crop in Cowell total P was about 24——33%. The effects of soil critical P buffering capacity (CBC), organic matter, and clay contents in soil were of great importance. CBC was obtained from the isotherm of P adsorption at equilibrium P concentration of 0.1μg/g, which is better than the MBC (maximum buffering capacity), when analyzing TAP. TAP can be estimated accurately by measuring some soil parameters (including Cowell total P) and using three-factor regression equation of which the decided coefficient (r~2) was above 80%, much higher than that of single-factor (cowell total P) equation.