Abstract
Purpose Biochar and silicate-enriched steel-slag, as agricultural and industrial waste materials, are used to improve soil physicochemical properties and soil fertility; however, there are few studies on the effects of their combined application to paddy fields on the formation of root Fe plaque. Materials and methods We tested the effects of four application rates (0, 300, 600 and 900 kg ha(-1)) of biochar-based silicate fertilizer (BSF) to early and late rice on root Fe plaque formation. Results and discussion Application of BSF increased soil total carbon and total nitrogen concentrations in late rice, and total phosphorus concentrations were increased by 47.03% at the jointing stage and 27.73% at the mature growth stage of early rice following application of BSF at 600 kg ha(-1). The three application treatments all significantly increased the abundance of soil iron-reducing bacteria (IRB) in late rice, and application of 600 kg of BSF ha(-1) increased IRB abundance by 52.16% and 66.59% at the jointing and mature growth stage, respectively. Both IRB abundance and IP concentration were positively correlated with Fe(II) and negatively correlated with Fe(III) in late rice. Soil Fe(II) concentration was positively correlated with water content, whereas Fe(III) concentration was negatively correlated. Conclusions Our study demonstrated that moderate inputs of BSF (600 kg ha(-1)) increased soil Fe reduction and subsequently promoted the formation of more soluble Fe(II) and iron plaque formation through soil fluidity and Fe(II) movement to roots. We suggest that the application of BSF to dry-wet rice paddies may contribute to reduction of agricultural pollution, improvement in soil conditions, and production of sustainable healthy food crops.