Supply capacity and depletion characteristics of accumulated phosphorus in fluvo-aquic soil

Objectives Long-term excessive fertilization greatly increased the accumulation of phosphorus in soil. Studying the availability and consumption characteristics of accumulated phosphorus resource could provide theoretical basis for exploring the phosphorus resources in soil and maintaining the sustainability of soil phosphorus fertility.

Methods Five plots with Olsen-P content of 1.2 mg/kg (L1), 14.3 mg/kg (L2), 27.6 mg/kg (L3), 55.4 mg/kg (L4) and 72.3 mg/kg (L5) were set up in the National Long-term Monitoring Station for fluvo-aquic Soil Fertility and Fertilizer Effects in Yuanyang, Henan Province of China. Nitrogen and potassium fertilizer without phosphate was applied to all the five plots for three consecutive years with 6 seasons of maize-wheat rotation. Crop yields, P uptake of crops, as well as consumption and change trend of soil Olsen-P were studied.

Results When the Olsen-P level of fluvo-aquic soil increased from low (L1) to high (L3), the yield of maize and wheat increased rapidly. The total yield of L1, L2, L4 and L5 treatments in six seasons were 37.4%, 82.8%, 104.7% and 102.3% of that of L3 treatment, respectively. Wheat was more sensitive to soil P supply than maize. The annual P requirement to ensure high yield of wheat-maize was 203.2 kg/hm². The total P supply in L1, L2 and L3 were 19.2%, 65.4% and 94.9% of crop P requirement for high yield, respectively, and the P supply in L4 and L5 could meet the requirement. The P uptake for producing 100 kg of wheat and maize grains were 0.48 kg and 0.34 kg, respectively. Under wheat-maize rotation, the seasonal consumption of soil available P showed a significant linear relationship with Olsen-P content (y = 0.1219x−0.1557, R² = 0.9894**), the season depletion amount of Olsen-P in L5, L4, L3 and L2 plot were 8.37 mg/kg, 7.06 mg/kg, 3.03 mg/kg, and 1.59 mg/kg, respectively. The depletion process fitted the exponential equation Y = 69.642e^−0.169x, which consumed 15.5% of the basic Olsen-P in each season.

Conclusions Long-term application of phosphorus fertilizer in large quantity could lead the accumulation of available P in fluvo-aquic soil to a very high level, but the crop yield will not continue increase when the P level is beyond the high level of available P. After the cessation of phosphorus fertilization, soil available P decreases exponentially and reaches the agronomic threshold value in merely about 9.1 seasons. The availability of soil P accumulated by high-rate application of phosphorus fertilizer decreases rapidly, the wheat yield starts to decrease significantly in the second year (the third season) after cessation of phosphorus fertilizer application. Therefore, sustainable and reasonable application of phosphorus fertilizer is necessary to maintain phosphorus fertility and phosphorus fertilizer efficiency in fluvo-aquic soil.