蔬菜地土壤磷提取及模拟径流中磷素潜在流失的影响

蔬菜地磷素流失是一种典型农业非点源污染类型。通过观测地表径流中溶解态反应磷(DRP)、生物可利用磷(BAP)可以监测土壤磷素流失程度。受到各种客观条件的限制,这两个指标比较难于获取,而土壤中的总磷(TP)、Olsen(OP)、Mehlich-1(M-1P)和水溶性磷(Pw)可以通过常规分析手段获取。本文选取27个典型蔬菜样地,分析测定各样地土壤中的总磷(TP)、Olsen(OP)、Mehlich-1(M-1P)和水溶性磷(Pw)四个磷提取变量,采用了经典方法计算土壤磷流失潜能指标——磷吸持饱和度(DPS)。同时采用模拟径流实验得出典型蔬菜样地地表径流样中溶解态反应磷(DRP)、生物可利用磷(BAP)。结果表明:M-1P、Pw与DPS呈极显著正相关,相关系数分别达到了0.85和0.74(p<0.01);而M-1P、Pw与DRP浓度相关系数(r2=0.843和0.786,p<0.01)大于TP、OP与DRP浓度的相关系数(r2=0.554和0.722,p<0.01)。结论认为,通过测定M-1P、Pw和计算DPS能比较准确、便捷地预测土壤径流磷素流失风险程度。

Testing of soil phosphorus from vegetable farm and the effects of phosphorus potential loss from simulated runoff

Soil phosphorus loss of vegetable farm was a typical nonpoint-source pollution. The quantities of soil phosphorus loss can be effectively received through long-term observation for soil surface runoff concentrations of dissolved reactive phosphorus (DRP) and bioavailable phosphorus (BAP). In practice, the indices of DRP and BAP was inconvenient due to the limitation of some impersonal reasons, then soil Total Phosphorus, Olsen-P, Mehlich1-P and Water-extractable Phosphorus all can be determined through laboratory conventional analysis. A study was initiated to collect twenty-seven typical soil samples of vegetable farm. Four soil testing phosphorus, including Total phosphorus (TP), Olsen phosphorus (OP), Mehlich-1 phosphorus (M-1P) and Water-extractable phosphorus (Pw), was compared to predict their effectiveness in predicting potential P release to water. Also, the degree of P saturation (DPS) was calculated, based on the method of ammonium oxalate extractable-P. Runoff simulations were conducted that runoff samples were collected from each vegetable soil sample and determined these concentrations of dissolved reactive P (DRP) and bioavailable P (BAP), the average means of 0.428 mg/L and 1.785 mg/L, respectively. The results showed that the r2 values for soil testing phosphorus by each extract method correlated with DPS were : 0.62 (TP), 0.67 (OP), 0.85 (M-1P), 0.74 (Pw). All correlations were significant (p<0.001), but the high r2 values of M-1P and Pw indicate better precision for predicting the potential for soil P loss to the environment. And the relationship between five variables with runoff losses of DRP and BAP. Good regression equations were derived relating STP to DRP and for each soil, as indicated by relatively high r2 values: 0.554 (TP), 0.722 (OP), 0.843 (M-1P), 0.786 (Pw). All correlations were significant (p<0.001), but the r2 values of M-1P and Pw were higher than those of TP and OP. Runoff levels of BAP estimated with iron oxide-impregnated paper were predicted well by various STP methods, but generally lower than those for runoff DRP. The results indicate that Mehlich1 soil test for environmental P could be developed to predict the risk of soil P release. Finally, the strong correlations of DRP and BAP with DPS were found (r2=0.653, 0.600 and p<0.001).