Changes in soil silicon forms and availability as affected by rice straw and its biochar

Abstract

Phytogenic silica (PhSi) is suggested to control silicon (Si) cycling in soil–plant systems in tropical and subtropical regions. However, the role of crop residues and its biochar as a source of available Si has not been well investigated in agricultural soils. In our study, we determined and compared the effects of rice straw and its biochar on soil Si forms and Si availability. Soil Si forms were characterised by a sequential extraction method, and soil Si availability was assessed by rice growth and soil Si extraction methods. A soil incubation experiment showed that the addition of rice straw and biochar increased plant‐available Si in soil (including mobile Si and adsorbed Si), as well as soil amorphous Si (especially in rice straw treatments). Moreover, this increase was more significant when higher Si (e.g., Si added at the rates of 1.6 and 2.0 g kg−1 soil) was added via rice straw and its biochar, which is most likely a result of PhSi dissolution. Rice‐straw biochar, particularly at higher Si addition rates, tended to have a higher efficiency in increasing soil Si availability than rice straw, mainly due to its greater proportion of readily labile Si. A rice growth pot experiment showed that it is difficult to determine the extent of Si dissolution from PhSi in rice straw using a short‐term experiment with a normal single‐season straw return rate, where the increased pH played a more crucial role in regulating soil Si availability. Our results imply that, in terms of enhancing Si availability, long‐term biochar application with abundant Si input is more effective than straw retention for improving soil fertility in subtropical and tropical regions with highly weathered soils. Highlights Effect of phytolith‐rich rice straw and its biochar on soil Si availability was studied. Biochar had greater efficiency in increasing plant‐available Si in soil than rice straw. Over the short term, Si dissolution from PhSi is insignificant with a typical single‐season straw return rate. Increased pH played a crucial role in regulating soil Si availability in a short‐term study.

Alkaline pre-treatment enhances silicon release efficiency of silicon-rich biochar

“…Therefore, it is a scientific question worth being explored how to permit efficient Si release from Si-rich plant residues. Although our previous study found that biochar has higher Si release efficiency than straw, its Si release may still be insufficient for crop growth under conventional dosage conditions (Yao et al 2022). Wang (Wang et al 2018a) and Wang (Wang et al 2022) have also found that the feedstock pretreatment with alkalis exposed phytoliths on the surface of feedstock significantly increase the plant-available Si of biochar.…”

“…A first-order model was used to describe Si mobilization in Si-rich biochar studied (Yao et al 2022):…”

“…Recent studies report that Si released from Si-rich biochar may be controlled by other surface components such as C and Si (Xiao et al 2014). The release of C1 pool in the first stage is the dissolution of non-phytolithic silica and the erosion of Si-O-Si bonds by hydroxyl ions, and the release of C2 pool in the second stage is the dissolution of phytolith particles (Wang et al 2018b;Yao et al 2022). In the soil incubation experiment, the dissolution of Si in the Si-rich biochar may preferentially replenish the Si pools in the soil, including Si_Acid Na acetate, Si_H2O2, and Si_NH2OH•HCl, thereby increasing their contents.…”

“…Biochar prepared from Si-accumulating plant biomass is known as Si-rich biochar (Wang et al 2018b;Li et al 2019a;Li and Delvaux 2019). Si-rich biomass and its biochar have been proven to increase the plant available Si pool and aboveground Si uptake in rice plants while increasing the crop yield (Liu et al 2014;Song et al 2014;Sandhya and Prakash 2019;Li et al 2019b;Yao et al 2022), which is important for alleviating silicon deficiency in cropland. However, high Si contents do not indicate high Si release due to the differences in the solubility (Wang et al 2019).…”

Rice straw biochar mitigates metal stress in maize and assists in the phytoattenuation of a slag-contaminated soil

“…Yao et al (2022) observed that the Si concentration in the rice shoots increased, on average, by 105% with the application of 0.3% RSB compared to the control (-Si). Si concentration in rice straw biochar can vary between 55.0 and 185.0 mg kg -1 ; therefore, RSB can increase the Si bioavailability in the soil and the accumulation of this element in crops (K and S, 2020;Li et al, 2019;Wang et al, 2019).…”