A comprehensive strategy for solving Cd risk while improving soil quality and rice yield in paddy fields: Co-utilizing green manure, rice straw, and biochar

Abstract

Cadmium (Cd) pollution in agricultural soil is a global concern. Traditional methods for controlling Cd pollution are mainly to add agents externally, with less attention on soil quality itself. Chinese milk vetch (MV) as a popular winter green manure can be utilized together with rice straw (RS) to improve soil quality and rice yield, and rape straw biochar (RB) is often used to alleviate the Cd risk in paddy soil. The location field experiment demonstrated that compared to co-utilizing MV and RS (MR), co-utilizing MR and RB (MRRB) increased the soil quality index by 12.2 %-34.1 %, and gradually improved rice yield along with experimental duration. During the four consecutive rice growing seasons, MRRB reduced brown rice Cd concentration by 29.8 %-61.3 %, compared to MR. Dissolved organic matter (DOM) was identified as the primary regulator of Cd bioavailability in soil-rice systems. Co-utilizing RB and DOM originated from the co-decomposition of MR (RB+DOM) reduced rice shoot Cd concentration by up to 54.4 % and 36.2 %, compared to RB and DOM alone, respectively. RB+DOM exhibited higher antioxidant enzyme activities, and regulated Cd-related gene expression, leading to reducing rice Cd uptake. RB+DOM increased Cd(II) adsorption capacity to 528 mg g^-1, 1.27 times higher than RB alone, due to more negative charge, specific surface area, and functional groups upon RB induced by DOM. Overall, this study provides a more practicable pathway for controlling soil Cd pollution as well as enhancing soil quality simultaneously, and gives novel insights for mitigating Cd pollution in rice when co-utilizing MV, RS, and RB.

Keywords: Cd transporter gene; Chinese milk vetch; DOM; Paddy soil; Soil quality.