Field test examines straw-biochar effects on black soil and soybean

A field experiment in cold-region black soil found that co-applying straw and biochar improved measured soil structure and regulated nutrient availability, while producing different effects on soil nutrients and soybean growth across four amendment treatments. The all-biochar treatment had the lowest bulk density, at 1.230 grams per cubic centimetre, and the highest porosity, at 52.72%. Its proportion of macroaggregates larger than 0.25 millimetres was 28.4% higher than under total straw return.

However, the four treatments did not differ significantly in soybean grain yield. The researchers examined total straw return, designated TS; high straw combined with low biochar, designated PS; low straw combined with high biochar, designated PB; and total biochar, designated TB. Soil measurements included bulk density, porosity and macroaggregate size, while the nutrient assessment distinguished nitrogen, phosphorus, potassium and dissolved organic carbon.

Soybean performance was evaluated through plant height, stem diameter, leaf area index and yield. The treatment receiving 13 tonnes per hectare of straw together with 6 tonnes per hectare of biochar, PB, recorded the highest numerical soybean yield among the four groups, but that numerical ranking was not accompanied by a statistically significant difference in grain yield. Biochar produced the clearest measured changes in the physical properties of the tested soil.

TB had the lowest bulk density and highest porosity, and its increase in macroaggregates larger than 0.25 millimetres reached 28.4% relative to TS. The nutrient responses followed a different pattern. TB and PB enhanced nitrogen and phosphorus availability throughout soybean growth, whereas TS and PS favored potassium and dissolved organic carbon.

Thus, the treatments did not have uniform effects across all measured components of soil fertility. Soybean growth characteristics were strongest in TB and PB. Plants in those treatments showed better plant height, stem diameter and leaf area index, corresponding with their higher nitrogen and phosphorus availability.

PB, containing 13 tonnes per hectare of straw and 6 tonnes per hectare of biochar, achieved the highest yield value, but the field results did not show a statistically significant separation in grain yield among the four co-application treatments. The authors characterized straw–biochar co-application as improving soil structure while regulating nutrients for early promotion and later stability, and identified the PB ratio as the best-performing option for improving black-soil fertility and increasing soybean yield. That conclusion concerns the tested field conditions and the specific amendment combinations; the results do not demonstrate that PB caused a significant grain-yield advantage over TS, PS or TB.

Subject of Research: Field evaluation of straw and biochar co-application effects on cold-region black soil nutrients and soybean growth

Article Title: Effects of co-application of straw and biochar on soil nutrients and soybean growth in black soil of cold regions

Article References: Lin, Y., Wang, M., Nie, T., Yan, H., Wang, Y., & Kong, P. (2026). Effects of co-application of straw and biochar on soil nutrients and soybean growth in black soil of cold regions. Frontiers in Soil Science, 6, 1849422. https://doi.org/10.3389/fsoil.2026.1849422

Image Credits: AI Generated

DOI: 10.3389/fsoil.2026.1849422

Keywords: biochar, straw return, cold-region black soil, soybean growth, soil nutrients, soil structure, bulk density, porosity, macroaggregates, field experiment, Effects, co-application