State Key Laboratory of Soil and Sustainable Agriculture, Institute of Soil Science, Chinese Academy of Sciences, P.O. Box 821, Nanjing, China; Department of Chemistry, University of Buea, P.O. Box 63, Buea, Cameroon.
State Key Laboratory of Soil and Sustainable Agriculture, Institute of Soil Science, Chinese Academy of Sciences, P.O. Box 821, Nanjing, China; College of Advanced Agricultural Sciences, University of Chinese Academy of Sciences, Beijing, 100049, China.
Chemosphere. 2022 Dec;309(Pt 1):136749. doi: 10.1016/j.chemosphere.2022.136749. Epub 2022 Oct 6.
Phosphorus (P) availability in highly weathered soils is significantly influenced by the contents of iron (Fe)/aluminum (Al) oxides, clay minerals, and organic matter. With the increasing interest in biofertilizers (e.g. chitosan), it is important to understand how they affect P adsorption profiles on colloids of weathered soils rich in Fe/Al oxides. Thus, the effect of chitosan on the adsorption of P to colloids of hematite, gibbsite, Oxisol, and Ultisol was studied through electrokinetic measurements, spectroscopic analysis, and adsorption edge/isotherm profiles. The presence of chitosan significantly improved the surface positive charge and the decreasing trend of surface positive charge was slower for chitosan-treated colloids compared to the control with increasing pH. At pH 5.0, all the colloids were positively charged, with the oxides containing more positve charges than the soil colloids. At this pH value, the surface coverage capacity of P was 99.1, 61.6, 50.5, and 37.5 mmol kg⁻ for Oxisol, Ultisol, hematite, and gibbsite, respectively. This suggests that clay minerals in soil colloids were vital in enhancing P adsorption. In the presence of chitosan, the surface coverage capacity of P was increased by 111%, 173%, 647%, and 488% for Oxisol, Ultisol, gibbsite, and hematite, respectively. Drawing inferences from spectroscopic analysis, citric acid desorption profile, and zeta potential analysis, we suggest that chitosan (CH) enhanced P adsorption by promoting the formation of (i) citric acid "undisplaceable" inner-sphere P complexes such as [Colloid-OP-O-CH] and [Colloid-OP-N-CH], (ii) citric acid "displaceable" outer-sphere P complexes such as {[Colloid-O-CH]-OP} and {[Colloid-N-CH]-OP}, and (iii) water "leachable or soluble" P complexes such as {[Colloid-CH]PO³⁻} and {[Colloid-OP]⁻CH}. Thus, applying chitosan as a biofertilizer (source of N) along with P in highly weathered soils could improve P availability while reducing P leaching.
磷（P）在高度风化土壤中的有效性受铁（Fe）/铝（Al）氧化物、粘土矿物和有机质含量的显著影响。随着人们对生物肥料（如壳聚糖）的兴趣日益浓厚，了解它们如何影响富含 Fe/Al 氧化物风化土壤胶体对 P 的吸附特性变得尤为重要。因此，通过动电测量、光谱分析和吸附边缘/等温线特性研究了壳聚糖对赤铁矿、三水铝石、氧化土和变性土胶体吸附 P 的影响。壳聚糖的存在显著提高了表面正电荷，且随着 pH 值的增加，壳聚糖处理胶体的表面正电荷下降趋势比对照胶体更慢。在 pH 5.0 时，所有胶体均带正电荷，其中氧化物的正电荷比土壤胶体多。在该 pH 值下，氧化土、变性土、赤铁矿和三水铝石胶体对 P 的表面覆盖容量分别为 99.1、61.6、50.5 和 37.5 mmol kg⁻。这表明土壤胶体中的粘土矿物对增强 P 吸附至关重要。在壳聚糖存在的情况下，氧化土、变性土、三水铝石和赤铁矿胶体对 P 的表面覆盖容量分别增加了 111%、173%、647%和 488%。从光谱分析、柠檬酸解吸曲线和动电电位分析推断，壳聚糖（CH）通过促进（i）柠檬酸“不可替代”内球 P 配合物如[Colloid-OP-O-CH]和[Colloid-OP-N-CH]、（ii）柠檬酸“可替代”外球 P 配合物如{[Colloid-O-CH]-OP}和{[Colloid-N-CH]-OP}和（iii）水“可浸出或可溶”P 配合物如{[Colloid-CH]PO³⁻}和{[Colloid-OP]⁻CH}的形成来增强 P 吸附。因此，在高度风化土壤中作为生物肥料（N 源）与 P 一起施用壳聚糖可提高 P 的有效性，同时减少 P 淋失。
