Effect of Continuous Vegetable Cultivation on Phosphorus Levels of Fluvo-Aquic Soils

Soil P status, inorganic P fractions, and P sorption properties were studied using sandy fluvo-aquic horticultural soils,which are high in organic matter content for vegetable production in comparison with a soil used for grain crop production in Zhengzhou, Henan Province, China. P fractions, Olsen-P, and OM were determined at different depths in the soil profile and sorption isotherm experiments were performed. Most P in excess of plant requirements accumulated in the topsoil and decreased with soil depth. Total P, inorganic P, and OM concentrations increased with continued horticultural use. Olsen-P concentrations in the 0-20 cm depth of horticultural soils were 9 to 25 times higher than those of the grain crop soil. A linear transformation of the Langmuir equation showed that the P adsorption maximum (491.3 mg P kg-i)and the maximum phosphate buffering capacity (162.1 L kg-1) for 80-100 cm were greater in the grain crop soil than the horticultural soils. Thus, the most immediate concern with excess P were in areas where heavy P fertilizer was used for vegetable crops and where soil P sorption capacities were low due to sandy soils and high organic matter content.

Soil P status, inorganic P fractions, and P sorption properties were studiedusing sandy fluvo-aquic horticultural soils, which are high in organic matter content for vegetableproduction in comparison with a soil used for grain crop production in Zhengzhou, Henan Province,China P fractions, Olsen-P, and OM were determined at different depths in the soil profile andsorption isotherm experiments were performed Most P in excess of plant requirements accumulated inthe topsoil and decreased with soildepth. Total P, inorganic P, and OM concentrations increased withcontinued horticultural use Olsen-P concentrations in the 0-20 cm depth of horticultural soils were9 to 25 times higher than those of the grain crop soil. A linear transformation of the Langmuirequation showed that the P adsorption maximum (491.3 mg P kg^(-1)) and the maximum phosphatebuffering capacity (162.1 L kg^(-1)) for 80--100 cm were greater in the grain crop soil than thehorticultural soils. Thus, the most immediate concern with excess P were in areas where heavy Pfertilizer was used for vegetable crops and where soil P sorption capacities were low due to sandysoils and high organic matter content.