Phosphorus fractions and adsorption–desorption in aggregates in coastal saline-alkaline paddy soil with organic fertilizer application

Abstract

Phosphorus (P), a potential limiting nutrient in soil, is an indispensable nutrient for crop growth and development. Effects of organic fertilizer on P fractions and its adsorption–desorption in soil aggregates were studied through a 6-year experiment in coastal saline-alkaline paddy field, which provided a theoretical basis in improving the retention capacity of P in soil. Four treatments were designed: (1) CK (no fertilization), NPK (only NPK chemical fertilizer), NPKC1 (NPK plus 450 kg C hm−2) and NPKC2 (NPK plus 900 kg C hm−2). Soil aggregates distribution, P fractions and adsorption–desorption of P were assessed. The application of organic fertilizer increased the concentrations of labile P (L-P), iron- and aluminum-bound P (Fe/Al-P), humic P (Hu-P), and residual P (Re-P) in soil aggregates, while the concentrations of calcium- and magnesium-bound P (Ca/Mg-P) and moderately organic P (Ml-Po) were decreased. L-P and Re-P were mainly enriched in large macroaggregates (LM,\u2009>\u20092.0 mm), Fe/Al-P, Hu-P, and Ml-Po were mainly enriched in microaggregates (MI, 0.053–0.25 mm). Small macroaggregates (SM, 0.25–2.0 mm) carried more Ca/Mg-P. Soil organic carbon (SOC) and exchangeable calcium (Ca) were the main factors affecting the distribution of P fractions in all soil aggregates, while in LM, the key factor was iron oxides (Feox), and in SM and silt\u2009+\u2009clay particles (SC,\u2009<\u20090.053 mm), exchangeable magnesium (Mg) was the main factor. The P retention capacity in soil aggregates was highest in NPKC1 treatment, while the leaching risk of P was higher in NKPC2 treatment. Redundancy analysis (RDA) showed that SOC, Feox, aluminum oxides (Alox), exchangeable Ca, and exchangeable Mg were positively correlated with the maximum adsorption capacity of P (Sm), while negatively correlated with the percentage of P (Prr). Multivariate linear regression analysis showed that Feox, Alox, and exchangeable Mg were the three important soil properties related to P adsorption–desorption in\u2009>\u20090.25-mm aggregates, while in\u2009<\u20090.25-mm aggregates, the main soil factors were SOC, exchangeable Ca, and exchangeable Mg. In the coastal saline-alkaline paddy field, moderate amount of organic fertilizer application (NPKC1) showed a better soil aggregate distribution and phosphorus (P) retention capacity, which provided a theoretical basis in improving soil fertility and reducing environmental pollution risk in the Yellow River Delta.