Frontiers in Soil Science · 2026
Effects of co-application of straw and biochar on soil nutrients and soybean growth in black soil of cold regions
Lin, Y., Wang, M., Nie, T., Yan, H., Wang, Y., Kong, P.
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Effects of co-application of straw and biochar on soil nutri…
Abstract
This field experiment investigated the combined effects of straw and biochar on Black Soil physicochemical properties and soybean growth in cold regions, with four treatments: total straw return (TS), high straw + low biochar (PS), low straw + high biochar (PB), and total biochar (TB). Results showed biochar amendments improved soil physical structure: TB had the lowest bulk density (1.230 g/cm 3 ) and highest porosity (52.72%), with >0.25 mm macroaggregates increased by 28.4% relative to TS. Nutrient supply differed by treatment: TB and PB enhanced nitrogen and phosphorus availability throughout growth, while TS and PS favored potassium and dissolved organic carbon. TB and PB promoted better soybean growth indices (plant height, stem diameter, LAI). PB treatment obtained the highest soybean yield value among all groups, but no statistically significant difference in grain yield was detected among the four straw-biochar combined treatments. Straw–biochar co-application synergistically improved soil structure and regulated nutrients for early promotion and late stability. The PB ratio (13 t/hm 2 straw + 6 t/hm 2 biochar) performed best, effectively improving Black Soil fertility and increasing soybean yield.
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This field experiment investigated the combined effects of straw and biochar on Black Soil physicochemical properties and soybean growth in cold regions, with four treatments: total straw return (TS), high straw + low biochar (PS), low straw + high biochar (PB), and total biochar (TB). Results showed biochar amendments improved soil physical structure: TB had the lowest bulk density (1.230 g/cm 3 ) and highest porosity (52.72%), with >0.25 mm macroaggregates increased by 28.4% relative to TS. Nutrient supply differed by treatment: TB and PB enhanced nitrogen and phosphorus availability throughout growth, while TS and PS favored potassium and dissolved organic carbon. TB and PB promoted better soybean growth indices (plant height, stem diameter, LAI). PB treatment obtained the highest soybean yield value among all groups, but no statistically significant difference in grain yield was detected among the four straw-biochar combined treatments. Straw–biochar co-application synergistically improved soil structure and regulated nutrients for early promotion and late stability. The PB ratio (13 t/hm 2 straw + 6 t/hm 2 biochar) performed best, effectively improving Black Soil fertility and increasing soybean yield.
This field experiment investigated the combined effects of straw and biochar on Black Soil physicochemical properties and soybean growth in cold regions, with four treatments: total straw return (TS), high straw + low biochar (PS), low straw + high biochar (PB), and total biochar (TB). Results showed biochar amendments improved soil physical structure: TB had the lowest bulk density (1.230 g/cm 3 ) and highest porosity (52.72%), with >0.25 mm macroaggregates increased by 28.4% relative to TS. Nutrient supply differed by treatment: TB and PB enhanced nitrogen and phosphorus availability throughout growth, while TS and PS favored potassium and dissolved organic carbon. TB and PB promoted better soybean growth indices (plant height, stem diameter, LAI). PB treatment obtained the highest soybean yield value among all groups, but no statistically significant difference in grain yield was detected among the four straw-biochar combined treatments. Straw–biochar co-application synergistically improved soil structure and regulated nutrients for early promotion and late stability. The PB ratio (13 t/hm 2 straw + 6 t/hm 2 biochar) performed best, effectively improving Black Soil fertility and increasing soybean yield.
Findings
What changed what, as the paper reports it. Grouped by the measured property. The largest groups are open; open the others as you need them.
soil bulk density
↓ 11
- decrease
PS, PB and TB, concordant biochar substitution variants specified per finding vs. TS, full straw return39t/ha, no biocharsignificant · 2025 R7 maturity · Bayan County, Harbin City · PS,PB,TB each versusTS; no depth stated; carbon inputs matched, differing straw/biochar masses; individualDuncanpairs not pooled test.
Numbers
- treatment 1.313 vs. control 1.37 g cm-3 (-4.161 %) · PS versusTS
- treatment 1.256 vs. control 1.37 g cm-3 (-8.321 %) · PB versusTS
- treatment 1.23 vs. control 1.37 g cm-3 (-10.22 %) · TB versusTS
Source · p. 9 “The biochar treatments exhibited reduced soil bulk density, increased porosity, and a higher content of macroaggregates”
total soil porosity
↑ 11
- increase
PS, PB and TB, concordant biochar substitution variants specified per finding vs. TS, full straw return39t/ha, no biocharsignificant · 2025 R7 maturity · Bayan County, Harbin City · PS,PB,TB each versusTS; no depth stated; individualDuncanpairs.
Numbers
- treatment 48.54 vs. control 46.57 % (+4.23 %) · PS versusTS
- treatment 50.12 vs. control 46.57 % (+7.623 %) · PB versusTS
- treatment 52.72 vs. control 46.57 % (+13.21 %) · TB versusTS
Source · p. 9 “The biochar treatments exhibited reduced soil bulk density, increased porosity, and a higher content of macroaggregates”
water-stable macroaggregates >0.25mm
1
- increase
TB,full biochar application9t/ha vs. TS, full straw return39t/ha, no biocharsignificance not stated · 2025 R7 maturity · Bayan County, Harbin City · Water-stable macroaggregate content>0.25mm; Figure1B testsseparatebins, not theirsum, so no alpha assignedtosum.
Numbers
- percent_change 28.4 · TB versusTS,>0.25mm macroaggregates
Source · p. 1 “with >0.25 mm macroaggregates increased by 28.4% relative to TS.”
Source · p. 11 “increased by 28.4% compared to the TS treatment.”
soil ammonium nitrogen
↑ 11
- increase
PS, PB and TB, concordant biochar substitution variants specified per finding vs. TS, full straw return39t/ha, no biocharsignificant · 2025 V5,R2,R5,R7 · Bayan County, Harbin City · TB/PB each versusTS atall4stages;PSversusTS onlyR2,R5,R7 (V5PSandTSsharec). No temporaltrend orTB/PBrankingclaimed.
Numbers
- treatment 10.25 vs. control 8.54 mg/kg (+20.02 %) · V5 · TB vsTS
- treatment 9.52 vs. control 8.54 mg/kg (+11.48 %) · V5 · PB vsTS
- treatment 9.25 vs. control 7.05 mg/kg (+31.21 %) · R2 · TB vsTS
- treatment 8.54 vs. control 7.05 mg/kg (+21.13 %) · R2 · PB vsTS
- treatment 7.84 vs. control 7.05 mg/kg (+11.21 %) · R2 · PS vsTS
- treatment 8.75 vs. control 6.51 mg/kg (+34.41 %) · R5 · TB vsTS
- treatment 8.22 vs. control 6.51 mg/kg (+26.27 %) · R5 · PB vsTS
- treatment 7.25 vs. control 6.51 mg/kg (+11.37 %) · R5 · PS vsTS
- treatment 12.84 vs. control 11.25 mg/kg (+14.13 %) · R7 · TB vsTS
- treatment 13.25 vs. control 11.25 mg/kg (+17.78 %) · R7 · PB vsTS
- treatment 12.25 vs. control 11.25 mg/kg (+8.889 %) · R7 · PS vsTS
Source · p. 9 “biochar treatments exhibited higher ammonium nitrogen and nitrate nitrogen contents in the early and middle growth stages compared to straw treatments.”
Source · p. 5 “PB took the lead with 13.25 mg/kg.”
soil nitrate nitrogen
↑ 11
- increase
PS, PB and TB, concordant biochar substitution variants specified per finding vs. TS, full straw return39t/ha, no biocharsignificant · 2025 V5,R2,R5,R7 · Bayan County, Harbin City · PS,PB,TB each versusTS atall4stages; individualDuncan.05; no betweenbiocharvariant ranking inferred from inconsistentfigure/text.
Numbers
- treatment 6.95 vs. control 5.26 mg/kg (+32.13 %) · V5 · TB vsTS
- treatment 6.25 vs. control 5.26 mg/kg (+18.82 %) · V5 · PB vsTS
- treatment 5.75 vs. control 5.26 mg/kg (+9.316 %) · V5 · PS vsTS
- treatment 5.84 vs. control 3.55 mg/kg (+64.51 %) · R2 · TB vsTS
- treatment 5.25 vs. control 3.55 mg/kg (+47.89 %) · R2 · PB vsTS
- treatment 4.21 vs. control 3.55 mg/kg (+18.59 %) · R2 · PS vsTS
- treatment 4.22 vs. control 2.98 mg/kg (+41.61 %) · R5 · TB vsTS
- treatment 4.85 vs. control 2.98 mg/kg (+62.75 %) · R5 · PB vsTS
- treatment 3.47 vs. control 2.98 mg/kg (+16.44 %) · R5 · PS vsTS
- treatment 8.31 vs. control 7.51 mg/kg (+10.65 %) · R7 · TB vsTS
- treatment 8.25 vs. control 7.51 mg/kg (+9.854 %) · R7 · PB vsTS
- treatment 8.02 vs. control 7.51 mg/kg (+6.791 %) · R7 · PS vsTS
Source · p. 5 “supplemented with biochar sustained stronger nitrate nitrogen retention capacity than sole straw returning throughout most growth stages”
available phosphorus
↑ 11
- increase
PS, PB and TB, concordant biochar substitution variants specified per finding vs. TS, full straw return39t/ha, no biocharsignificant · 2025 V5,R2,R5,R7 · Bayan County, Harbin City · TB/PB versusTS all4stages;PSversusTS V5,R2,R7only (R5PSbsharesTSb).
Numbers
- treatment 17.15 vs. control 15.55 mg/kg (+10.29 %) · V5 · TB vsTS
- treatment 16.82 vs. control 15.55 mg/kg (+8.167 %) · V5 · PB vsTS
- treatment 16.22 vs. control 15.55 mg/kg (+4.309 %) · V5 · PS vsTS
- treatment 18.57 vs. control 15.83 mg/kg (+17.31 %) · R2 · TB vsTS
- treatment 17.82 vs. control 15.83 mg/kg (+12.57 %) · R2 · PB vsTS
- treatment 16.57 vs. control 15.83 mg/kg (+4.675 %) · R2 · PS vsTS
- treatment 15.25 vs. control 14.15 mg/kg (+7.774 %) · R5 · TB vsTS
- treatment 15.16 vs. control 14.15 mg/kg (+7.138 %) · R5 · PB vsTS
- treatment 19.52 vs. control 17.52 mg/kg (+11.42 %) · R7 · TB vsTS
- treatment 19.16 vs. control 17.52 mg/kg (+9.361 %) · R7 · PB vsTS
- treatment 18.15 vs. control 17.52 mg/kg (+3.596 %) · R7 · PS vsTS
Source · p. 9 “biochar treatments consistently led in available phosphorus content”
Source · p. 5 “The TB treatment was 15.25 mg/kg, and the PB, PS, and TS treatments were 15.16 mg/kg, 14.52 mg/kg, and 14.15 mg/kg, respectively.”
available potassium
↓ 11
- decrease
PS, PB and TB, concordant biochar substitution variants specified per finding vs. TS, full straw return39t/ha, no biocharsignificant · 2025 V5,R2,R7 · Bayan County, Harbin City · TB/PB versusTS V5,R2,R7;PSversusTS R2,R7only; V5PSsharesa. EntireR5excluded because proseNSconflictswithFigure3Bletters; not an all-seasonclaim.
Numbers
- treatment 188.2 vs. control 215.9 mg/kg (-12.79 %) · V5 · TB vsTS
- treatment 195.2 vs. control 215.9 mg/kg (-9.558 %) · V5 · PB vsTS
- treatment 178.2 vs. control 195.8 mg/kg (-9.028 %) · R2 · TB vsTS
- treatment 182.5 vs. control 195.8 mg/kg (-6.827 %) · R2 · PB vsTS
- treatment 188.2 vs. control 195.8 mg/kg (-3.922 %) · R2 · PS vsTS
- treatment 178.2 vs. control 195.2 mg/kg (-8.701 %) · R7 · TB vsTS
- treatment 182.1 vs. control 195.2 mg/kg (-6.682 %) · R7 · PB vsTS
- treatment 188.1 vs. control 195.2 mg/kg (-3.612 %) · R7 · PS vsTS
Source · p. 10 “the available potassium contents in the PS and PB treatments increased with the amount of straw applied”
Source · p. 10 “The sole biochar treatment had the lowest available potassium content”
dissolved organic carbon
↓ 11
- decrease
PS, PB and TB, concordant biochar substitution variants specified per finding vs. TS, full straw return39t/ha, no biocharsignificant · 2025 V5,R2,R5,R7 · Bayan County, Harbin City · PBvsTSall4stages;TBvsTS V5/R5only (TBabsharesa atR2/R7);PSvsTS R5only. PrintedDOCabsolutevaluesonlyTS; othermeansnotreadfromcharts orcomputedfrompercentageranges.
Source · p. 6 “The TS treatment had the highest DOC content at all stages”
Source · p. 6 “The PB and TB treatments had relatively low DOC contents”
soybean plant height
↑ 11
- increase
PS, PB and TB, concordant biochar substitution variants specified per finding vs. TS, full straw return39t/ha, no biocharsignificant · 2025 V5,R2,R5,R7 · Bayan County, Harbin City · PBvsTSall4stages;TBvsTS V5/R2/R7only;PSvsTS R2/R7only. V5PSsharesb,R5PS/TBabsharesTSb. Meanpairsfromtextincm,notconvertedfromfigurem; R5/R7TSmeansunprinted.
Numbers
- treatment 57.9 vs. control 44.2 cm (+31 %) · V5 · TB vsTS
- treatment 56.4 vs. control 44.2 cm (+27.6 %) · V5 · PB vsTS
- treatment 97.4 vs. control 75.6 cm (+28.84 %) · R2 · TB vsTS
- treatment 91.1 vs. control 75.6 cm (+20.5 %) · R2 · PB vsTS
- treatment 87.5 vs. control 75.6 cm (+15.74 %) · R2 · PS vsTS
Source · p. 7 “The PB treatment consistently followed, while the TS treatment was the lowest at all stages.”
soybean stem diameter
↑ 11
- increase
PS, PB and TB, concordant biochar substitution variants specified per finding vs. TS, full straw return39t/ha, no biocharsignificant · 2025 V5,R2,R5 · Bayan County, Harbin City · TB/PBvsTS V5/R2;PSvsTS R2;PBvsTS R5. R5TB/PSsharebwithTS; entireR7excluded forfigure/texttreatment-label/directionconflict. OnlyV5hascompleteprintedmeanpairs.
Numbers
- treatment 0.69 vs. control 0.54 cm (+27.78 %) · V5 · TB vsTS
- treatment 0.68 vs. control 0.54 cm (+25.93 %) · V5 · PB vsTS
Source · p. 10 “The TB and PB treatments exhibited higher plant height, stem diameter, and leaf area index than the straw treatments in most growth stages”
leaf area index
↑ 11
- increase
PB,13t/ha straw+6t/ha biochar vs. TS, full straw return39t/ha, no biocharsignificant · 2025 V5,R2,R5 · Bayan County, Harbin City · PBvsTSonly; Figure4C PBa/TSb atall3stages; TBbsharesTSb, so textclaimofTBsignificantadvantage notassigned. PrintedPB/TSmeanspreservedastext;noTB/PBvalues swapped to reconcilechart.
Numbers
- treatment 2.37 vs. control 2.12 (+11.79 %) · V5
- treatment 3.58 vs. control 3.23 (+10.84 %) · R5
Source · p. 10 “The TB and PB treatments exhibited higher plant height, stem diameter, and leaf area index than the straw treatments in most growth stages”
pods per plant
↑ 11
- increase
TB,full biochar application9t/ha vs. TS, full straw return39t/ha, no biocharsignificant · 2025 mature harvest (methodsR9; ResultsFigure5) · Bayan County, Harbin City · TBavsTSb; PBabsharesb andnotincluded; PSbnotincluded.
Numbers
- treatment 39 vs. control 35.3 pods/plant (+10.48 %)
Source · p. 8 “TB had the highest value of 39.0 pods”
Source · p. 8 “PS and TS had 36.0 pods and 35.3 pods respectively”
seed number per plant
↑ 11
- increase
PS, PB and TB, concordant biochar substitution variants specified per finding vs. TS, full straw return39t/ha, no biocharsignificant · 2025 mature harvest · Bayan County, Harbin City · PS,PB,TB eachavsTSb inFigure5; nointervariantdifferenceclaimed.
Numbers
- treatment 90.7 vs. control 88.3 seeds/plant (+2.718 %) · PS vsTS
- treatment 98.3 vs. control 88.3 seeds/plant (+11.33 %) · PB vsTS
- treatment 95.7 vs. control 88.3 seeds/plant (+8.381 %) · TB vsTS
Source · p. 9 “treatments incorporated with biochar exhibited superior performance in pod number and seed number compared with sole straw returning treatments”
100-seed weight
= 11
- no effect
PS, PB and TB, concordant biochar substitution variants specified per finding vs. TS, full straw return39t/ha, no biocharnot significant · 2025 mature harvest · Bayan County, Harbin City · PS,PB,TB eachversusTS; allsamea inFigure5, explicitposthocnull; 100seedassay, not convertedto1000.
Numbers
- treatment 21.84 vs. control 22.78 g/100seeds (-4.126 %) · PS vsTS
- treatment 22.03 vs. control 22.78 g/100seeds (-3.292 %) · PB vsTS
- treatment 22.36 vs. control 22.78 g/100seeds (-1.844 %) · TB vsTS
Source · p. 8 “No significant differences in 100-seed weight were observed among treatments.”
grain yield
= 11
- no effect
PS, PB and TB, concordant biochar substitution variants specified per finding vs. TS, full straw return39t/ha, no biocharnot significant · 2025 mature harvest · Bayan County, Harbin City · PS,PB,TB eachversusTS; Figure5all4a, explicitmultipletestnull; PBhighestnumericalvalueisnotasignificantyieldgain; conflictedrelativepercentagesomitted.
Numbers
- treatment 1,977 vs. control 1,992 kg/ha (-0.7401 %) · PS vsTS
- treatment 2,062 vs. control 1,992 kg/ha (+3.552 %) · PB vsTS
- treatment 2,050 vs. control 1,992 kg/ha (+2.925 %) · TB vsTS
Source · p. 8 “multiple comparisons revealed no statistically significant yield differences across all four treatments marked with the same lowercase letter a.”
Set-up
Treatments
- straw and biochar combined application ratioBiochar
- PS, PB and TB, concordant biochar substitution variants specified per findingBiocharTS, full straw return39t/ha, no biocharResidue incorporationPB,13t/ha straw+6t/ha biocharBiocharTB,full biochar application9t/haBiochar
Measured
- soil bulk densityBulk density
- Unit
- g cm-3
- Method
- Core cutter
- total soil porosityTotal porosity
- Unit
- %
- Method
- Derived from bulk density and particle density2.65g/cm3; printed values preserved
- water-stable macroaggregates >0.25mmWater-stable macroaggregates
- Unit
- %
- soil ammonium nitrogenNH4+/Ammonia
- Unit
- mg/kg
- Method
- 1mol/LKCl1:10,AA3colorimetric
- soil nitrate nitrogenNO3-/Nitrate
- Unit
- mg/kg
- Method
- 1mol/LKCl1:10,AA3colorimetric
- available phosphorus
- Unit
- mg/kg
- Method
- Molybdenum-antimonycolorimetry,AA3; extracting reagent unstated
- available potassiumExchangeable/available potassium
- Unit
- mg/kg
- Method
- Neutral1mol/LNH4OAc;atomic absorption
- dissolved organic carbonDissolved organic carbon/DOC
- Unit
- mg/kg
- Method
- Freshsoil:water1:5,0.45membranefilter,TOCanalyzer
- soybean plant heightPlant height
- Unit
- cm
- soybean stem diameterStem diameter
- Unit
- cm
- leaf area indexLeaf area index (LAI)
- Method
- LP80canopyanalyzer
- pods per plantPod number
- Unit
- pods/plant
- seed number per plantGrain number
- Unit
- seeds/plant
- 100-seed weightThousand kernel weight
- Unit
- g/100seeds
- Method
- Massof100seeds; no conversion to1000seeds
- grain yieldYield
- Unit
- kg/ha
Sites
Bayan County, Harbin City
- Location
- Bayan County, Harbin City, Heilongjiang Province, southern Songnen Plain, China; latitude printed45°77'N is invalid and not corrected
- Climate
- 3.6 °C mean annual temperature529 mm annual precipitation
- Soil
- Black Soil · Chinese
- Land use
- soybean fieldsArable land
- Management on the whole site
- Dongnong 252 soybeanSoybean/Glycine max, agricultural rotary tiller incorporationRotary tillage
| Depth | Texture | Clay | pH | Organic C | Bulk density |
|---|---|---|---|---|---|
| initial soil (depth not stated) | loam | – | – | – | – |
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