Optimizing phosphorus (P) application to agricultural soils is fundamental to crop production and water quality protection. We sought to relate soil P tests and P sorption characteristics to both crop yield response to P application and environmentally critical soil P status. Barley (Hordeum vulgare L.) was grown in pot experiments with 45 soils of different P status. Half the pots were fertilized at 20 kg P ha-1 , and half received no P. Soils were extracted with ammonium lactate, sodium bicarbonate (Olsen P), dilute salt (0.0025 M CaCl2 ), and diffusive gradient in thin films. Soil adsorption coefficients were determined using the Freundlich isotherm equation, and the degree of P saturation was determined from both oxalate and ammonium lactate extracted Fe, Al, and P. All soil P analyses showed a nonlinear and significant relationship with yield response to P application, and all analyses manifested a threshold value above which no P response was observed. For the commonly used ammonium lactate test, inclusion of Al and Fe improved prediction of plant-available soil P. The threshold for yield response coincided with the environmentally critical values determined from the degree of P saturation. Results support the conclusion that soil P levels for which no P application is needed also have elevated risk of P loss to runoff.

中文翻译：

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土壤有效磷预测：作物生产与水质保护相结合

优化农业土壤中磷 (P) 的施用是作物生产和水质保护的基础。我们试图将土壤磷测试和磷吸附特性与作物产量对磷应用的​​反应和环境临界土壤磷状态联系起来。大麦 (Hordeum vulgare L.) 在盆栽试验中用 45 种不同磷状态的土壤种植。一半的盆以 20 kg P ha-1 施肥，另一半不施磷。用乳酸铵、碳酸氢钠 (Olsen P)、稀盐 (0.0025 M CaCl2) 和薄膜扩散梯度提取土壤。土壤吸附系数使用 Freundlich 等温方程确定，P 饱和度由草酸盐和乳酸铵提取的 Fe、Al 和 P 确定。所有土壤磷分析都显示出与产量响应对磷应用的​​非线性和显着关系，并且所有分析都显示出一个阈值，高于该阈值没有观察到磷响应。对于常用的乳酸铵试验，加入铝和铁提高了对植物有效土壤磷的预测。产量响应的阈值与由磷饱和度确定的环境临界值一致。结果支持以下结论：不需要施磷的土壤磷水平也会增加磷流失到径流的风险。产量响应的阈值与由 P 饱和度确定的环境临界值一致。结果支持以下结论：不需要施磷的土壤磷水平也会增加磷流失到径流的风险。产量响应的阈值与由 P 饱和度确定的环境临界值一致。结果支持以下结论：不需要施磷的土壤磷水平也会增加磷流失到径流的风险。