亚热带可变电荷土壤磷素淋失临界点及其与土壤特性的关系

选取我国亚热带地区16种典型可变电荷土壤,通过室内模拟试验测定其磷素(P)淋失临界点的Olsen-P含量,以及可能对其构成有影响的8个化学性质指标(pH、CEC、粘粒、有机质、交换性钙、镁和铁铝氧化物含量),以探讨可变电荷土壤P淋失临界点的特点及其与土壤相关性质的关系,并评价当前的P淋失潜在风险.结果表明:可变电荷土壤P淋失临界点的Olsen-P含量(56 ～ 123 mg·kg-1)差异很大,旱地土壤临界点Olsen-P含量主要集中在低值区间(＜60 mg·kg-1),而水稻土临界点Olsen-P含量集中在高值区间(＞80 mg·kg-1);旱地土壤P淋失风险高于水稻土.主成分分析显示,可变电荷土壤的pH、粘粒、CEC、有机质、交换性钙镁、氧化铁铝等化学性质同时对其临界点Olsen-P含量构成正的或负的影响.因此,临界点Olsen-P含量与单一因素的回归分析不仅不能够确切地反映临界点Olsen-P含量与这些化学性质的关系(与pH、CEC、粘粒、交换性钙镁含量无显著相关),甚至与理论上的关联相违(与氧化铁铝含量呈负相关).与以往研究结果比较,可变电荷土壤在旱作和稻作下的P淋失临界点的Olsen-P含量都普遍高于永久电荷土壤,研究的16种可变电荷土壤的实际Olsen-P含量也远低于临界点Olsen-P含量,由此推断南方地区耕作土壤的P淋失风险仍较小.

Phosphorus leaching change point of subtropical variable-charge soils and its relations with soil properties

This study was to understand the characteristics of the P leaching potential of variable-charge soils and to evaluate their P leaching risks.Sixteen soils which were representatives of variable-charge soils in subtropical China, as determined by their phosphorus (P) leaching change point (the soil P concentration where P moves from soil to water), were collected.Basic properties e.g.pH, CEC, clay and organic matter, exchangeable Ca²⁺ and Mg²⁺, Fe₂O₃ and Al₂O₃ concentrations were determined.There were large variations in Olsen P concentrations (56~123 mg·kg^-1) at the P leaching change points.The Olsen P concentrations of upland soils were mainly quite small (< 60 mg·kg^-1) and were considerably higher in paddy soils (> 80 mg·kg^-1).Therefore the P leaching potential was lower in the paddy soils than in the upland soils.Principal Component Analysis indicated that soil chemical properties can produce both positive and negative effects on Olsen P concentration.This explains why linear correlations between Olsen P concentrations and single soil chemical properties are generally non-significant. Such analyses cannot realistically reflect the effects of pH, CEC, and the concentrations of clay, exchangeable Ca²⁺ and Mg²⁺ (no significant correlations), and even give contradictory results with Fe₂O₃ and Al₂O₃ (negative correlations).Olsen P concentrations at the change points of the variable charge soils were higher than the commonly measured in permanent-charge soils.Because the Olsen-P concentrations in all of the variable charge soils were considerably less than the Olsen P concentrations at the change point, it is suggested that potential risks of P leaching from variable-charge soils are small in subtropical China.