Response of Tomato on Calcareous Soils to Different Seedbed Phosphorus Application Rates

<正>Field experiments were conducted with five rates (0, 75, 150, 225, and 450 kg P2O5 ha-1) of seedbed P fertilizer application to investigate the yield of tomato in response to fertilizer P rate on calcareous soils with widely different levels of Olsen P (13-142 mg kg-1) at 15 sites in some suburban counties of Beijing in 1999. Under the condition of no P fertilizer application, tomato yield generally increased with an increase in soil test P levels, and the agronomic level for soil testing P measured with Olsen method was 50 or 82 mg kg-1 soil to achieve 85% or 95% of maximum tomato yield, respectively. With regard to marketable yield, in the fields where Olsen-P levels were < 50 mg kg-1, noticeable responses to applied P were observed. On the basis of a linear plateau regression, the optimum seedbed P application rate in the P-insufficient fields was 125 kg P2O5 ha-1 or about 1.5-2 times the P removal from harvested tomato plants. In contrast, in fields with moderate (50 < Olsen P < 90 mg kg-1) or high (Olsen P > 90 mg kg-1) available P, there was no marked effect on tomato fruit yield. Field survey data indicated that in most fields with conventional P management, a P surplus typically occurred. Thus, once the soil test P level reached the optimum for crop yield, it was recommended that P fertilizer application be restricted or eliminated to minimize negative environmental effects.