Rice grown on the soda saline-sodic soils of Northeast China’s Songnen Plain faces a double burden: toxic sodium, high alkalinity and poor soil structure that stunt the crop, and nitrogen fertilizer that is largely wasted. In those paddies, nitrogen use efficiency sits at only 20 to 25 percent, well below the 30 to 35 percent typical of conventional fields. A two-year field experiment now reports that turning rice straw into biochar and working it into the soil does a better job of easing that stress and improving the crop’s nitrogen economy than plowing the raw straw directly back into the ground.
The trial, conducted from 2023 to 2024 at the Soda Salinization-Alkalization Research Farm of Jilin University in Baicheng City, Jilin Province, compared three straw management options: complete straw removal, direct return of rice straw at 7.2 tonnes per hectare, and return of straw-derived biochar at 2.4 tonnes per hectare, the amount left after carbonizing the same mass of straw. Each option was crossed with four nitrogen rates: no nitrogen, 125, 225 and 325 kilograms of nitrogen per hectare, with 225 representing the local farmer standard. The design used a split-plot layout with three replications, giving 36 plots of 24 square meters each, and the rice variety was the salt-tolerant japonica cultivar Changbai 9.
The biochar itself was produced by pyrolyzing rice straw at 450 degrees Celsius for four hours in an oxygen-free environment. According to the researchers, that processing matters. After carbonization, the nutrient content of the material, particularly nitrogen, phosphorus, potassium and magnesium, is significantly higher than in raw straw, while its sodium content is substantially reduced. Its porous structure and high specific surface area also give it strong adsorption capacity, allowing it to trap sodium ions, hold them in micropores and promote the leaching of soluble salts. Raw straw, by contrast, must decompose before it releases nutrients, and decomposition is exactly what saline-sodic soils inhibit.
The physiological results were consistent across both years and all nitrogen levels. Both straw return and biochar return lowered leaf sodium concentration and the sodium-to-potassium ratio while raising potassium concentration, but the biochar effect was stronger. Averaged over treatments, biochar cut leaf sodium by 13.36 percent at heading stage and 17.13 percent at filling stage relative to straw removal, and by 4.23 and 6.91 percent relative to direct straw return. The sodium-to-potassium ratio fell by 25.17 and 28.57 percent at the two stages compared with straw removal, and by 7.16 and 10.58 percent compared with straw return. Potassium content rose by 15.72 percent under biochar at heading stage versus 10.71 percent under straw return, with similar gaps at filling stage.
The treatments also reshaped the crop’s stress chemistry. Both amendments reduced the oxidative damage markers malondialdehyde, hydrogen peroxide and superoxide anion, with biochar again ahead: malondialdehyde fell 22.19 percent under biochar versus 12.73 percent under straw return at heading stage. Soluble protein and proline, osmoprotective compounds, increased, as did the activities of the antioxidant enzymes superoxide dismutase and catalase, which followed the consistent ordering biochar greater than straw return greater than straw removal. Soluble sugar, peroxidase and ascorbate peroxidase declined under both treatments. The authors interpret the drop in soluble sugar and the rise in proline and soluble protein as a shift away from stress-induced osmotic adjustment toward a less constrained metabolic state.
Nitrogen metabolism responded in parallel. Both straw practices upregulated a set of key genes including OsNR1, OsNRT1;1, OsNRT2;1, OsGS1;1, OsGS2, OsGDH2 and OsFd-GOGAT, and raised the activities of the enzymes nitrate reductase, glutamine synthetase and glutamate synthase. Across the two-year study, nitrate reductase activity rose by 13.75 to 28.55 percent, glutamine synthetase by 7.01 to 16.04 percent and glutamate synthase by 14.37 to 24.67 percent relative to straw removal, with biochar consistently the stronger treatment. Glutamate dehydrogenase activity, by contrast, declined under both treatments, a pattern the authors link to a shift from the stress-associated GDH pathway back toward the more efficient GS/GOGAT assimilation cycle.
Those enzymatic and genetic gains translated into measurable nitrogen savings. Compared with straw removal, average total nitrogen accumulation rose by 22.44 to 39.58 percent under biochar and by 12.39 to 49.84 percent under straw return, while nitrogen use efficiency climbed by 16.49 to 22.07 percent under biochar and 11.60 to 23.18 percent under straw return. Nitrogen translocation from stems and leaves to the grain also improved, as did the nitrogen transport contribution rate, with biochar generally outperforming straw return. The strongest responses appeared under the 225-kilogram nitrogen rate, and the effects grew more pronounced in the second year, suggesting a cumulative benefit as the amendments interact with the soil over successive seasons.
Yield followed the same hierarchy. Grain yield under biochar was 16.25 percent higher than under straw removal and 4.04 percent higher than under direct straw return, and the biochar-versus-removal difference was statistically significant. Notably, the yield advantage of straw return over removal appeared only in the second year; in 2023 there was no significant difference between those two treatments. Yield rose with nitrogen rate, with the 125, 225 and 325-kilogram rates lifting yields 27.70, 65.80 and 73.51 percent above the no-nitrogen control. The yield gains tracked increases in panicle number, up 16.99 percent under biochar, and spikelets per panicle, up 11.20 percent, while seed-setting rate and thousand-grain weight were unaffected.
Structural equation modeling helped the team untangle the causal chain. For direct straw return, the dominant route to higher yield ran through improved ionic balance and stress physiology, with nitrogen metabolism acting largely as a compensatory driver; stress-related components carried the greatest explanatory power. Under biochar, the model pointed to a sequential pathway from ameliorated stress physiology through enhanced nitrogen metabolism to improved nitrogen efficiency and finally elevated grain yield, with nitrogen metabolism enzymes and protective enzymes explaining most of the variance. Both the direct and indirect effects of biochar were stronger than those of straw return.
The authors conclude that combining straw-derived biochar with 225 kilograms of nitrogen per hectare is the more effective strategy for mitigating soda saline-alkali stress, boosting nitrogen use efficiency and raising grain yield in these paddy soils. They also flag the limits of the evidence: the trial covers a single site and two years, and the effects of straw and biochar amendments depend on feedstock type, soil conditions and regional environment. Multi-site, multi-year trials across different soil types are needed, they write, to validate the mechanisms and the differential effects observed here before the practice can be generalized.
Subject of Research: A field experiment comparing straw-derived biochar with direct straw return for alleviating soda saline-sodic stress and improving nitrogen use efficiency in rice.
Article Title: Straw-derived biochar was more effective than direct straw return in mitigating soda saline-sodic stress and improving nitrogen use efficiency in rice grown in saline-sodic fields
Article References: Jin, F., Wang, C., Wang, X., Song, Y., Wang, Q., Liu, H., Wang, H., Wu, T., Jiang, W., Lan, Y., Cao, T., Hou, X., Hua, S., & Huang, C. (2026). Straw-derived biochar was more effective than direct straw return in mitigating soda saline-sodic stress and improving nitrogen use efficiency in rice grown in saline-sodic fields. Biochar, 8(1), Article 125. https://doi.org/10.1007/s42773-026-00619-7
Image Credits: AI Generated
DOI: 10.1007/s42773-026-00619-7
Keywords: biochar, straw return, saline-sodic soil, rice, nitrogen use efficiency, soil salinity, soda saline-alkali stress, Songnen Plain, antioxidant enzymes, nitrogen metabolism, grain yield, field experiment
News Source: Alan Morgan. (October 30, 2026). Biochar beats straw return for rice on salty soda soils. Scienmag.
