Agronomy · 2026
Dynamics of Soil Organic Carbon and Nitrogen Fractions in Dryland Wheat Fields as Affected by Tillage Practices on the Loess Plateau of China
Wang, L., Li, H., Xu, T., Yang, X., Dong, F., Yan, S., Yan, Q.
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Dynamics of Soil Organic Carbon and Nitrogen Fractions in Dr…
Abstract
Soil organic carbon (SOC) and total nitrogen (TN) are key indicators of soil fertility; however, the dynamics of carbon (C) and nitrogen (N) fractions during winter wheat growth under different tillage systems remain poorly understood. This study examined the effects of three tillage practices: no tillage (NT), subsoiling tillage (SS), and deep tillage (DT) on four soil organic carbon fractions (SOC, soil organic carbon; EOC, easily oxidized organic carbon; DOC, dissolved organic carbon; POC, particulate organic carbon) and four nitrogen fractions (TN, total nitrogen; NO3−-N, nitrate nitrogen; NH4+-N, ammonium nitrogen; DON, dissolved organic nitrogen) across five winter wheat growth stages (sowing, overwintering, jointing, filling and harvest) in the 0–50 cm soil profile. The results showed that SOC, its labile fractions, and TN all decreased with increasing soil depth, with tillage effects mainly confined to the 0–20 cm layer. SS achieved the highest SOC and TN contents in the topsoil, while NT and SS significantly enhanced the surface enrichment of C and N. In contrast, DT promoted more uniform nutrient distribution into the 30–50 cm subsoil. DON continuously accumulated throughout the growing season with faster accumulation rates under SS and NT; DOC peaked at the jointing stage, while EOC and NH4+-N followed a consistent “decline–recovery–decline” seasonal pattern. SS yielded the highest total SOC stock (166.20 t ha−1) in the 0–50 cm profile, particularly in the 0–30 cm layer. Correlation analysis showed that the coupling relationships among C and N indicators varied with soil depth, with the strongest positive correlation between SOC and EOC in the topsoil. Both SS and DT maintained higher soil water content (SWC) than NT in the 20–50 cm layers throughout the experimental period. In conclusion, SS emerges as the optimal balanced tillage strategy for dryland wheat fields on the Loess Plateau, simultaneously improving topsoil fertility, water retention, and C sequestration; meanwhile, DT is more effective for enhancing subsoil water and nutrient conditions. These findings provide a scientific basis for targeted tillage management to sustain soil fertility and productivity in rainfed dryland farming systems.
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Soil organic carbon (SOC) and total nitrogen (TN) are key indicators of soil fertility; however, the dynamics of carbon (C) and nitrogen (N) fractions during winter wheat growth under different tillage systems remain poorly understood. This study examined the effects of three tillage practices: no tillage (NT), subsoiling tillage (SS), and deep tillage (DT) on four soil organic carbon fractions (SOC, soil organic carbon; EOC, easily oxidized organic carbon; DOC, dissolved organic carbon; POC, particulate organic carbon) and four nitrogen fractions (TN, total nitrogen; NO3−-N, nitrate nitrogen; NH4+-N, ammonium nitrogen; DON, dissolved organic nitrogen) across five winter wheat growth stages (sowing, overwintering, jointing, filling and harvest) in the 0–50 cm soil profile. The results showed that SOC, its labile fractions, and TN all decreased with increasing soil depth, with tillage effects mainly confined to the 0–20 cm layer. SS achieved the highest SOC and TN contents in the topsoil, while NT and SS significantly enhanced the surface enrichment of C and N. In contrast, DT promoted more uniform nutrient distribution into the 30–50 cm subsoil. DON continuously accumulated throughout the growing season with faster accumulation rates under SS and NT; DOC peaked at the jointing stage, while EOC and NH4+-N followed a consistent “decline–recovery–decline” seasonal pattern. SS yielded the highest total SOC stock (166.20 t ha−1) in the 0–50 cm profile, particularly in the 0–30 cm layer. Correlation analysis showed that the coupling relationships among C and N indicators varied with soil depth, with the strongest positive correlation between SOC and EOC in the topsoil. Both SS and DT maintained higher soil water content (SWC) than NT in the 20–50 cm layers throughout the experimental period. In conclusion, SS emerges as the optimal balanced tillage strategy for dryland wheat fields on the Loess Plateau, simultaneously improving topsoil fertility, water retention, and C sequestration; meanwhile, DT is more effective for enhancing subsoil water and nutrient conditions. These findings provide a scientific basis for targeted tillage management to sustain soil fertility and productivity in rainfed dryland farming systems.
Soil organic carbon (SOC) and total nitrogen (TN) are key indicators of soil fertility; however, the dynamics of carbon (C) and nitrogen (N) fractions during winter wheat growth under different tillage systems remain poorly understood. This study examined the effects of three tillage practices: no tillage (NT), subsoiling tillage (SS), and deep tillage (DT) on four soil organic carbon fractions (SOC, soil organic carbon; EOC, easily oxidized organic carbon; DOC, dissolved organic carbon; POC, particulate organic carbon) and four nitrogen fractions (TN, total nitrogen; NO3−-N, nitrate nitrogen; NH4+-N, ammonium nitrogen; DON, dissolved organic nitrogen) across five winter wheat growth stages (sowing, overwintering, jointing, filling and harvest) in the 0–50 cm soil profile. The results showed that SOC, its labile fractions, and TN all decreased with increasing soil depth, with tillage effects mainly confined to the 0–20 cm layer. SS achieved the highest SOC and TN contents in the topsoil, while NT and SS significantly enhanced the surface enrichment of C and N. In contrast, DT promoted more uniform nutrient distribution into the 30–50 cm subsoil. DON continuously accumulated throughout the growing season with faster accumulation rates under SS and NT; DOC peaked at the jointing stage, while EOC and NH4+-N followed a consistent “decline–recovery–decline” seasonal pattern. SS yielded the highest total SOC stock (166.20 t ha−1) in the 0–50 cm profile, particularly in the 0–30 cm layer. Correlation analysis showed that the coupling relationships among C and N indicators varied with soil depth, with the strongest positive correlation between SOC and EOC in the topsoil. Both SS and DT maintained higher soil water content (SWC) than NT in the 20–50 cm layers throughout the experimental period. In conclusion, SS emerges as the optimal balanced tillage strategy for dryland wheat fields on the Loess Plateau, simultaneously improving topsoil fertility, water retention, and C sequestration; meanwhile, DT is more effective for enhancing subsoil water and nutrient conditions. These findings provide a scientific basis for targeted tillage management to sustain soil fertility and productivity in rainfed dryland farming systems.
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
↑ 1↓ 1= 13
- increase
NT and SS, agreeing conservation-tillage comparisons vs. DT with incorporated wheat residuessignificant · 0–20 cm · afterharvestJune2022 · Hongbu National Experimental Station · 0–20cm,Fig5actualletters:0–10NTa/SSavsDTb;10–20NTa/SSbvsDTc. No chartmeanestimates.
Source · p. 9 “In the 0–10 and 10–20 cm depths, soil bulk density showed a sequence of NT > SS > DT”
- no effect
NT and SS, agreeing conservation-tillage comparisons vs. DT with incorporated wheat residuesnot significant · 20–30 cm · afterharvestJune2022 · Hongbu National Experimental Station · 20–30cm,Fig5allthree sharea,individualsharedletters plus explicitnullsentence,not omnibusalone.
Source · p. 9 “The maximum soil bulk density was observed in the 20–30 cm soil layer with no significant difference among tillage treatments”
- decrease
NT and SS, agreeing conservation-tillage comparisons vs. DT with incorporated wheat residuessignificant · 30–50 cm · afterharvestJune2022 · Hongbu National Experimental Station · 30–50cmNTvsDT;40–50cmSSvsDT. Fig5NTbvsDTa30–40;SSa sharesDTaat30–40so excluded despite generalprose. At40–50NTb/SSbvsDTa.
Source · p. 9 “In the 30–50 cm deep soil layer, BD under DT was significantly higher than that under NT and SS (p < 0.05)”
SOC content
↑ 12
- increase
NT and SS, agreeing conservation-tillage comparisons vs. DT with incorporated wheat residuessignificant · 0–10 cm · 2021–2022,sowing–harvest · Hongbu National Experimental Station · 0–10cm; NTandSS compared separatelywithDT;Fig1nodifferenceletters,butp11explicitlystates significantpairincrease. Residuesplacement/ratesdifferbetweensystems.
Source · p. 11 “SS and NT significantly increased SOC content in the 0–10 cm surface layer”
Source · p. 5 “In the 0–10 cm layer, SS consistently maintained the highest SOC content throughout the growth stages, followed by NT, while DT showed the lowest values”
- increase
NT and SS, agreeing conservation-tillage comparisons vs. DT with incorporated wheat residuessignificance not stated · 10–20 cm · 2021–2022,sowing–harvest · Hongbu National Experimental Station · 10–20cm; particularlysowingandfilling;Fig1nopairwisetests,not given surfacealpha.
Source · p. 5 “In the 10–20 cm layer, both SS and NT treatments exhibited higher SOC contents compared with DT, particularly during the sowing and filling stages”
easily oxidized organic carbon (EOC)
↑ 22
- increase
NT and SS, agreeing conservation-tillage comparisons vs. DT with incorporated wheat residuessignificant · 0–20 cm · 2021–2022,sowing–harvest · Hongbu National Experimental Station · 0–20cm; explicit pair statement,not omnibusANOVA; two individuallyreported systems.
Source · p. 5 “in the 0–20 cm soil layer, where SS and NT significantly enhanced EOC content compared with DT”
- increase
with SOC contentsignificant · 0–20 cm · 2021–2022 · Hongbu National Experimental Station · 0–20cm,Fig4a/bexplicit .68*/.57*. Deeper .48/.32/.13unstarred,not included in significantrun. nnotinferredfromsamplingdesign.
Numbers
- r = 0.68 · 0–10 cm
- r = 0.57 · 10–20 cm
Source · p. 9 “SOC and EOC showed a positive correlation across all soil layers, and this correlation weakened with increasing soil depth”
total nitrogen (TN)
2
- increase
NT and SS, agreeing conservation-tillage comparisons vs. DT with incorporated wheat residuessignificance not stated · 0–10 cm · earlygrowthstages,2021–2022 · Hongbu National Experimental Station · 0–10cm, earlystages; nopairwisetestsFig2. Do notextendto10–20cmwhereaveragesdonotagree.
Source · p. 5 “SS and NT treatments generally maintained higher TN levels compared with DT in the 0–10 cm layer during early stages”
- decrease
NT and SS, agreeing conservation-tillage comparisons vs. DT with incorporated wheat residuessignificance not stated · 20–50 cm · 2021–2022,sowing–harvest · Hongbu National Experimental Station · 20–50cm,oppositedirectiontosurface;Fig2no pairwiseletters.
Source · p. 5 “in the deeper soil layers (20–50 cm), the TN content under DT was relatively higher than that under SS and NT”
total SOC stock
2
- increase
SS with mostly surface residues and partial incorporation vs. DT with incorporated wheat residuessignificance not stated · 0–50 cm · meanoffivegrowthstages,2021–2022 · Hongbu National Experimental Station · 0–50cm,fixeddepthstocksC×BD×H×0.1,not equivalentsoilmass; Table1no pairwisetests. Generalcontent/enrichmentalpha doesnot testprofile stock.
Numbers
- treatment 166.2 vs. control 122 t ha-1 (+36.18 %) · 0–50 cm
Source · p. 8 “The SOC stocks in the 0–50 cm soil layer under NT, SS and DT were 149.82, 166.20 and 122.04”
- increase
SS with mostly surface residues and partial incorporation vs. NT with surface wheat residuessignificance not stated · 0–50 cm · meanoffivegrowthstages,2021–2022 · Hongbu National Experimental Station · 0–50cm,fixeddepthstocksC×BD×H×0.1,not equivalentsoilmass; SSmaximum vsNTasnamedabstract; Table1no pairwisetests.
Numbers
- treatment 166.2 vs. control 149.8 t ha-1 (+10.93 %) · 0–50 cm
Source · p. 8 “The SOC stocks in the 0–50 cm soil layer under NT, SS and DT were 149.82, 166.20 and 122.04”
SOC layer contribution to total profile stock
↑ 12
- increase
NT and SS, agreeing conservation-tillage comparisons vs. DT with incorporated wheat residuessignificant · 0–10 cm · meanoffivegrowthstages,2021–2022 · Hongbu National Experimental Station · 0–10cmstockshare of0–50cmfixeddepthstock; explicit stratificationresult,notsurfacecontent orrelative%gain. Significancefromoriginalresultstatementp10,noTable1marks.
Numbers
- treatment 27.67 vs. control 24.23 % (+14.2 %) · 0–10 cm · NTvsDT
- treatment 30.98 vs. control 24.23 % (+27.86 %) · 0–10 cm · SSvsDT
Source · p. 10 “The significantly higher contribution of the 0–10 cm layer to SOC, TN, EOC, and DON stocks under NT and SS confirms a pronounced stratification effect”
Source · p. 8 “conservation tillage (SS and NT) generally exhibited higher contribution rates compared with DT”
- decrease
NT and SS, agreeing conservation-tillage comparisons vs. DT with incorporated wheat residuessignificance not stated · 30–50 cm · meanoffivegrowthstages,2021–2022 · Hongbu National Experimental Station · 30–50cmstockshareof0–50cmfixeddepthstock; testsnotreported; oppositedirectiontosurfaceshare.
Numbers
- treatment 15.11 vs. control 16.14 % (-6.382 %) · 30–40 cm · NTvsDT
- treatment 11.62 vs. control 14.25 % (-18.46 %) · 40–50 cm · NTvsDT
- treatment 12.91 vs. control 16.14 % (-20.01 %) · 30–40 cm · SSvsDT
- treatment 10.01 vs. control 14.25 % (-29.75 %) · 40–50 cm · SSvsDT
Source · p. 8 “in the deeper layers (e.g., 30–50 cm), the contribution rates of SOC and TN under DT were generally higher than those under SS and NT”
TN layer contribution to total profile stock
↑ 12
- increase
NT and SS, agreeing conservation-tillage comparisons vs. DT with incorporated wheat residuessignificant · 0–10 cm · meanoffivegrowthstages,2021–2022 · Hongbu National Experimental Station · 0–10cmstockshareof0–50cmfixeddepthstock; explicit stratificationresultp10,not totalNstocksignificance.
Numbers
- treatment 29.59 vs. control 22.87 % (+29.38 %) · 0–10 cm · NTvsDT
- treatment 30.13 vs. control 22.87 % (+31.74 %) · 0–10 cm · SSvsDT
Source · p. 10 “The significantly higher contribution of the 0–10 cm layer to SOC, TN, EOC, and DON stocks under NT and SS confirms a pronounced stratification effect”
Source · p. 8 “conservation tillage (SS and NT) generally exhibited higher contribution rates compared with DT”
- decrease
NT and SS, agreeing conservation-tillage comparisons vs. DT with incorporated wheat residuessignificance not stated · 30–50 cm · meanoffivegrowthstages,2021–2022 · Hongbu National Experimental Station · 30–50cmstockshareof0–50cmfixeddepthstock,testsnotreported; oppositedirectiontosurfaceshare.
Numbers
- treatment 13.26 vs. control 17.66 % (-24.92 %) · 30–40 cm · NTvsDT
- treatment 11.81 vs. control 14.89 % (-20.69 %) · 40–50 cm · NTvsDT
- treatment 12.19 vs. control 17.66 % (-30.97 %) · 30–40 cm · SSvsDT
- treatment 11.34 vs. control 14.89 % (-23.84 %) · 40–50 cm · SSvsDT
Source · p. 8 “in the deeper layers (e.g., 30–50 cm), the contribution rates of SOC and TN under DT were generally higher than those under SS and NT”
soil water content
2
- increase
SS and DT, agreeing tilled-system water comparisons vs. NT with surface wheat residuessignificance not stated · 20–50 cm · overwintering–harvest,2021–2022 · Hongbu National Experimental Station · 20–50cm,SSandDT individuallyvsNT,Fig6no pairwiseletters; reportedgeneraldirection,not uniformsignificance. Residueplacementandrateconfoundedwithtillage.
Source · p. 9 “The SS and DT treatments showed higher SWC compared with NT in 20–50 cm soil layers throughout the experimental period”
- increase
SS with mostly surface residues and partial incorporation vs. NT with surface wheat residuessignificance not stated · 0–10 cm · jointing–harvest,2021–2022 · Hongbu National Experimental Station · 0–10cm,SSvsNTduringlatestages; explicitp14direction,Fig6no pairwisetests ortranscribedchartmeans.
Source · p. 14 “SS consistently maintained higher water content in the 0–10 cm surface layer during the late growth stages (jointing–harvest)”
particulate organic carbon (POC)
↑ 11
- increase
SS with mostly surface residues and partial incorporation vs. DT with incorporated wheat residuessignificant · 0–10 cm · filling,2021–2022 · Hongbu National Experimental Station · 0–10cm,SSvsDT; explicit originalresult p11 qualifiesFig1dwhichhasnosignificancemarks; not allstages.
Source · p. 5 “the SS treatment showed a substantial increase in POC at the filling stage, reaching its maximum value, whereas DT remained relatively low”
Source · p. 11 “SS significantly increased POC content in the 0–10 cm layer at the filling stage”
dissolved organic nitrogen (DON)
1
- increase
NT and SS, agreeing conservation-tillage comparisons vs. DT with incorporated wheat residuessignificance not stated · 0–10 cm · fillingandharvest,2021–2022 · Hongbu National Experimental Station · 0–10cm,lateDONcontents; fasteraccumulationdescribescontext,not acomputedrateor anotherfinding;Fig2no pairwiseletters.
Source · p. 6 “In the 0–10 cm layer, the SS and NT treatments exhibited a faster accumulation rate of DON, resulting in noticeably higher values than DT at the late growth”
Source · p. 7 “stages (filling and harvest)”
Set-up
Treatments
- tillage and residue management systemsTillage system
- NT with surface wheat residuesZero tillageSS with mostly surface residues and partial incorporationSubsoilingDT with incorporated wheat residuesDeep tillageNT and SS, agreeing conservation-tillage comparisonsConservation tillageSS and DT, agreeing tilled-system water comparisonsTillage system
Measured
- SOC contentSoil organic carbon
- Unit
- g kg-1
- Method
- K2Cr2O7oxidation,titrationwithFeSO4; heatingnotstated
- easily oxidized organic carbon (EOC)Permanganate oxidizable Carbon/POXC
- Unit
- mg kg-1
- Method
- 333mmol/LKMnO4oxidation; retain figure's mg/kgunit,not aninferredcorrection
- particulate organic carbon (POC)Particulate organic carbon
- Unit
- g kg-1
- Method
- sodiumhexametaphosphatedispersion
- total nitrogen (TN)Total Nitrogen
- Unit
- g kg-1
- dissolved organic nitrogen (DON)Dissolved organic Nitrogen
- Unit
- mg kg-1
- Method
- K2SO4extraction,TOCanalyzer
- total SOC stockSoil organic carbon
- Unit
- t ha-1
- Method
- C×BD×H×0.1;fivefixeddepthlayers0–50cm;noequivalentmasscorrection
- SOC layer contribution to total profile stockSoil organic carbon
- Unit
- %
- Method
- 100×layerstock/0–50cmstock
- TN layer contribution to total profile stockTotal Nitrogen
- Unit
- %
- Method
- 100×layerstock/0–50cmstock
- soil bulk densityBulk density
- Unit
- g cm-3
- Method
- IntactcoresafterJune2022harvest,105°C48h
- soil water contentGravimetric water content
- Unit
- W/W,%
- Method
- Gravimetric,105°C48h
Sites
Hongbu National Experimental Station
- Location
- Hongbu National Experimental Station, Shanxi Province, Loess Plateau, China36.32° N, 111.82° E
- Climate
- 12.2 °C mean annual temperature481 mm annual precipitation
- Land use
- dryland winter wheat fieldsArable land
- Management on the whole site
- winter wheat Jinmai92Wheat/Triticum aestivum
| Depth | Texture | Clay | pH | Organic C | Bulk density |
|---|---|---|---|---|---|
| 0–20 cm | loess silt loam | 13.6 % | – | – | – |
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