Long-term biochar addition significantly decreases rice rhizosphere available phosphorus and its release risk to the environment

Abstract

Phosphorus (P) availability, diffusion, and resupply processes can be altered by biochar addition in flooded rice rhizosphere, which controls the risk of P release to the environment. However, there are few in-situ investigations of these rhizospheric processes and effects. To explore the effects of biochar addition on soil P availability, high-resolution dialysis (HR-Peeper), diffusive gradients in thin films (DGT), and zymography techniques were used to provide direct evidence in the rice rhizosphere at the sub-millimeter scale. Long-term (9-years) field and greenhouse pot experiments demonstrated that biochar addition notably decreased the soluble/labile P and Fe concentrations in rice rhizosphere (vs. no biochar addition; CK) based on the results of Peeper, DGT, and two-dimensional imaging of labile P fluxes. DGT-induced fluxes in the soil/sediment (DIFS) model and sediment P release risk index (SPRRI) further indicated that biochar addition decreased the diffusion and resupply capacity of P from soil solid to the solution, thereby decreasing P release risk to the environment. These processes were dominated by Fe redox cycling and the hydrolysis of Al (hydro)oxides that greatly increased the unavailable P (Ca-P and residual-P). Additionally, greenhouse pot experiments (without additional biochar) showed that the previous long-term biochar addition significantly increased soil phosphatase activity, due to an adaptive-enhancing response to P decrease in the rhizosphere zone. The in-situ study on the biogeochemical reactions of P in the rice rhizosphere may provide a new and direct perspective to better evaluate the biochar addition and potential benefits to agricultural soils. Graphical Abstract

Long-term biochar application influences phosphorus and associated iron and sulfur transformations in the rhizosphere

“…Notably, prior studies have tended to focus more on soil processes and less on rhizosphere processes. In our investigation using the DGT technique, we discovered a significant reduction in rice rhizosphere available P after 9 years of biochar addition in the field (Chen et al 2022). However, the lack of available data on long-term effects of biochar on nutrient cycling, particularly in the rhizosphere zone, has been limiting our ability to include biochar amendment as one of the best management practices on a broad scale across the globe (Wei et al 2019).…”

“…The urea and potassium chloride (KCl) application dozes were 250 kg N ha −1 (in a ratio of 3:4:3 at basal, tillering, and jointing stages) and 60 kg K 2 O ha −1 , respectively. Detailed information on biochar, soil and fertilization methods used in the field experiment can be found in Chen et al (2022). The biochar used in the field was derived from rice straw and produced through pyrolysis at a temperature of 500 °C for 8 h, with a heating rate of 5 °C min −1 .…”

Use of diffusive gradients in thin-film technique to predict the mobility and transfer of nutrients and toxic elements from agricultural soil to crops—an overview of recent studies

“…In all cases, the DGT was reported as a useful tool in assessing the impact of amendments on P availability. Chen et al (2022) studied the fluxes of P in the rice rhizosphere using DGT, high-resolution dialysis (HR-Peeper), and zymography techniques. DGT measurements indicated that long-term biochar addition to the soil significantly diminished the diffusion and resupply capacity of P from the soil solid phase to the soil solution, thus lessening the risk of P release into the environment (Chen et al 2022).…”

“…DGT has the potential to be deployed in situ, although this direction has not yet been extensively used until now due to potential issues related to the deficiency of parameter control, mainly regarding the soil moisture. Several reports on particular cases of DGT application to wet soils, such as rice fields, were published (Wang et al 2021 ; Chen et al 2022 ; Wang et al 2022a ).…”

“…The main findings from these researches are detailed below. The effects on P availability were tested after the addition of biochar (Chen et al 2022 ; Yang and Lu 2022 ), or other organic and inorganic fertilizers containing P (Nobile et al 2018 ; Kang et al 2021 ; Wenzel et al 2022 ; Zhang et al 2023 ). In all cases, the DGT was reported as a useful tool in assessing the impact of amendments on P availability.…”