Crop productivity in cold waterlogged paddy fields can be constrained by chronic flooding stress and low temperature. Farmers typically use chemical fertilizer to improve crop production, but this conventional fertilization is not very effective in a cold waterlogged paddy field. Biochar amendment has been proposed as a promising management approach to eliminating these obstacles. However, little is known about the performance of biochar when combined with N fertilizer and P fertilizer in cold waterlogged soils. The aim of this study was, therefore, to assess the main effects and interactive effects of rice straw biochar, N and P fertilizer on rice growth and soil properties in a cold waterlogged paddy field. The field treatments consisted of a factorial combination of two biochar levels (0 and 2.25 t ha⁻¹), two N fertilizer levels (120.0 and 180.0 kg ha⁻¹) and two P fertilizer levels (37.5 and 67.5 kg ha⁻¹) which were arranged in a randomized block design, with three replicates. Results confirmed that biochar application caused a significant increase in the soil pH due to its liming effect, while this application resulted in a significant decrease in soil exchangeable cations, such as exchangeable Ca, Mg, Al and base cations. The interactive effect of N fertilizer, P fertilizer and biochar was significant for soil total N. Moreover, a negative effect of biochar on the internal K use efficiency suggested that K uptake into rice may benefit from biochar application. According to the partial Eta squared values, the combined application of N fertilizer and biochar was as effective as pure P fertilization at increasing straw P uptake. The addition of biochar to farmers’ fertilization practice treatment (180.0 kg N ha⁻¹, 67.5 kg P₂O₅ ha⁻¹ and 67.5 kg K₂O ha⁻¹) significantly increased rice yield, mainly owing to improvements in grains per panicle. However, notable effects of biochar on rice yield and biomass production were not detected. More studies are required to assess the long-term behavior of biochar in a cold waterlogged paddy field. This study may lay a theoretical foundation for blended application of biochar with fertilizer in a cold waterlogged paddy field.

Global plant sulphur (S) deficiency is increasing because of a reduction in sulphate-based fertiliser application combined with continuous S withdrawal during harvest. Here, we applied ¹³C, ¹⁵N, ¹⁴C, and ³⁵S quad labelling of the S-containing amino acids cysteine (Cys) and methionine (Met) to understand S cycling and microbial S transformations in the soil. The soil microorganisms absorbed the applied Cys and Met within minutes and released SO₄²⁻ within hours. The SO₄²⁻ was reutilised by the MB within days. The initial microbial utilisation and SO₄²⁻ release were determined by amino acid structure. Met released 2.5-fold less SO₄²⁻ than Cys. The microbial biomass retained comparatively more C and S from Met than Cys. The microorganisms decomposed Cys to pyruvate and H₂S whereas they converted Met to α-ketobutyrate and S-CH₃. The microbial stoichiometries of C, N, and S derived from Cys and Met were balanced after 4 d by Cys-derived SO₄²⁻ uptake and Met-derived CO₂ release. The microbial C:N:S ratio dynamics showed rapid C utilisation and loss, stable N levels, and S accumulation. Thus, short-term organic S utilisation by soil microorganisms is determined by amino acid structure whilst long-term organic S utilisation by soil microorganisms is determined by microbially controlled stoichiometry.

Soil organic carbon is crucial for climate mitigation and agroecosystem sustainability, yet its depletion is concerning and its response to long-term fertilization remains unclear. Here we leverage the Broadbalk Classical Experiment at Rothamsted (UK), the world’s longest-running continuous winter wheat fertilization trial, along with ¹⁴C labelling, metagenomics and metabolomics to determine how 180 years of nitrogen (N) and phosphorus (P) fertilization impact soil organic carbon dynamics. Compared with no fertilization, long-term P, N and combined NP fertilization increased the soil organic carbon content by 10%, 22% and 28%, respectively. P application alone disproportionately increased microbial respiration (37%) and biomass (20%), limiting stable carbon formation and slightly increasing labile carbon. N application alone increased microbial carbon use and necromass accumulation efficiency, increasing mineral-associated carbon build-up. Combined NP fertilization enhanced plant-derived carbon inputs and the transformation of labile carbon into stable carbon, increasing soil organic carbon quantity and stability. A meta-analysis of the effects of fertilization duration on soil organic carbon revealed that N and P fertilization globally increased cropland soil organic carbon by 21% and 13%, and these promoting effects decreased before increasing after 16 and 34 years, respectively. Overall, long-term mineral fertilization can effectively enhance soil carbon sequestration.