ABSTRACT Selenium (Se) is an essential nutrient for humans and animals, but is toxic at high concentrations in leaves. It is chemically similar to phosphorus (P), an essential plant macronutrient. The objective of this pot experiment was to investigate the effects of P- and Se-application rate on alfalfa growth and P and Se uptake in loessial soil, and reveal the changing processes of soil P and Se fractions. The results indicated that Se concentration in alfalfa was significantly influenced by the interaction of P- and Se-application rate. In the loessial soil, an optimal P- and Se-application rate is 5 mg kg−1 and 2 mg kg−1, respectively for plant growth and the maximum P and Se accumulation in alfalfa. Besides, concentrations of exchangeable Se and organic-matter-bound Se in soil decreased, as the P-application rate increased, whereas concentrations of soluble Se and iron oxide-bound Se increased. The addition of P fertilizer reduced soil pH, affecting the changing processes of soil P and Se fractions, thus promoting the activation of Fe-P and the transformation of exchangeable Se to iron oxide-bound Se. These findings will help in understanding of forage P and Se accumulation and provide the guide for cultivating Se-enriched forage.

中文翻译：

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碱性土壤中磷酸盐和亚硒酸盐的相互作用和苜蓿的积累（Medicago sativa L.）

摘要 硒 (Se) 是人类和动物的必需营养素，但在叶子中高浓度时会产生毒性。它在化学上与磷 (P) 相似，磷是一种必需的植物常量营养素。本盆栽试验的目的是研究磷硒施用量对紫花苜蓿生长和黄土中磷硒吸收的影响，揭示土壤磷硒含量的变化过程。结果表明，施磷量和施硒量相互作用显着影响苜蓿中的硒浓度。在黄土土壤中，最佳的磷和硒施用量分别为 5 mg kg-1 和 2 mg kg-1，对于植物生长和苜蓿中磷和硒的最大积累。此外，随着施磷量的增加，土壤中可交换硒和有机质结合硒的浓度降低，而可溶性硒和氧化铁结合硒的浓度增加。磷肥的添加降低了土壤pH值，影响了土壤P和Se组分的变化过程，从而促进了Fe-P的活化和可交换性Se向氧化铁结合Se的转化。这些发现将有助于了解牧草磷和硒的积累，为培育富硒牧草提供指导。