Earthworm inoculation and straw return decrease the phosphorus adsorption capacity of soils in the Loess region, China

Abstract

Loess Plateau is important for maize production in China. Therefore, a good understanding of soil phosphorus (P) behavior in the Loess region is crucial for optimizing fertilization in its agriculture systems. To date, research on factors influencing P adsorption/desorption has mainly focused on fertilization. Widespread application of straw return and increasing soil fauna in agricultural croplands inevitably affect soil P behavior either directly or indirectly in this area. However, less attention has been focused on these effects and their interactions. Here, a field plot experiment was performed based on a completely randomized design to investigate the response of P adsorption-desorption characteristics to the presence/absence of earthworms and straw return. Treatments included: (1) control without earthworms and straw (E0S0); (2) treatment with only earthworms (E1S0); (3) treatment with only straw (E0S1); (4) treatment with both earthworms and straw. The Langmuir model was superior to the Freundlich model in interpreting the P adsorption data and allowed better evaluation of the maximum P adsorption values. The maximal P adsorption, P adsorption affinity constant, and maximum buffer capacity in the earthworm and straw treatments were 2.4-8.3%, 8.3-13.9%, and 2.2-26.3% lower than those in E0S0. The readily desorbable P, standard P requirement, and degree of P saturation increased by 15.6-44.3%, 13.1-23.1%, and 4.4-16.5%, respectively, in earthworm and straw treatments. Additionally, earthworm inoculation and straw return treatments significantly increased total soil P, Olsen P, soil organic carbon, free Fe₂O₃, and CaCO₃ contents and specific surface area of the soil. Redundancy analysis showed that soil organic carbon explained most (14.7%) of the total variation in P adsorption and desorption. These results show that combining earthworm inoculation with straw return can effectively reduce soil P adsorption capacity, increase its P desorption capacity, and thus, increase its available P content. These results provide a scientific basis for improving the utilization efficiency of soil P.

Keywords: Earthworm inoculation; Loess; Phosphorus adsorption; Phosphorus desorption; Straw return.