Maguire Rory O, Sims J Thomas
Department of Plant and Soil Sci., Univ. of Delaware, Newark, DE 1917-1303, USA.
J Environ Qual. 2002 Sep-Oct;31(5):1601-9. doi: 10.2134/jeq2002.1601.
Subsurface pathways can play an important role in agricultural phosphorus (P) losses that can decrease surface water quality. This study evaluated agronomic and environmental soil tests for predicting P losses in water leaching from undisturbed soils. Intact soil columns were collected for five soil types that a wide range in soil test P. The columns were leached with deionized water, the leachate analyzed for dissolved reactive phosphorus (DRP), and the soils analyzed for water-soluble phosphorus (WSP), 0.01 M CaCl2 P (CaCl2-P), iron-strip phosphorus (FeO-P), and Mehlich-1 and Mehlich-3 extractable P, Al, and Fe. The Mehlich-3 P saturation ratio (M3-PSR) was calculated as the molar ratio of Mehlich-3 extractable P/[Al + Fe]. Leachate DRP was frequently above concentrations associated with eutrophication. For the relationship between DRP in leachate and all of the soil tests used, a change point was determined, below which leachate DRP increased slowly per unit increase in soil test P, and above which leachate DRP increased rapidly. Environmental soil tests (WSP, CaCl2-P, and FeO-P) were slightly better at predicting leachate DRP than agronomic soil tests (Mehlich-1 P, Mehlich-3 P, and the M3-PSR), although the M3-PSR was as good as the environmental soil tests if two outliers were omitted. Our results support the development of Mehlich-3 P and M3-PSR categories for profitable agriculture and environmental protection; however, to most accurately characterize the risk of P loss from soil to water by leaching, soil P testing must be fully integrated with other site properties and P management practices.
土壤深层路径在导致农业磷（P）流失进而降低地表水水质方面可能发挥重要作用。本研究评估了用于预测原状土壤水淋溶过程中磷流失的农艺学和环境土壤测试方法。采集了五种土壤类型的原状土柱，这些土壤的土壤有效磷含量范围广泛。用去离子水淋洗土柱，分析淋出液中的溶解性反应磷（DRP），并分析土壤中的水溶性磷（WSP）、0.01M氯化钙提取磷（CaCl2-P）、铁条提取磷（FeO-P）以及Mehlich-1和Mehlich-3提取的磷、铝和铁。计算Mehlich-3磷饱和度比率（M3-PSR），即Mehlich-3提取磷/[铝+铁]的摩尔比。淋出液中的DRP浓度经常高于与富营养化相关的浓度。对于淋出液中DRP与所有使用的土壤测试之间的关系，确定了一个变化点，低于该点时，淋出液DRP随土壤测试磷单位增加而缓慢增加，高于该点时，淋出液DRP迅速增加。环境土壤测试（WSP、CaCl2-P和FeO-P）在预测淋出液DRP方面略优于农艺学土壤测试（Mehlich-1磷、Mehlich-3磷和M3-PSR），不过如果剔除两个异常值，M3-PSR与环境土壤测试效果相当。我们的研究结果支持为实现盈利性农业和环境保护制定Mehlich-3磷和M3-PSR类别；然而，为了最准确地表征土壤磷通过淋溶流失到水体的风险，土壤磷测试必须与其他场地特性和磷管理实践充分结合。
