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No‐tillage farming combined with temporary cattle grazing is becoming a common practice in parts of South America. We quantified the effects of no‐tillage and winter grazing of annual ryegrass (Lolium multiflorum Lam.) on soil carbon and nitrogen stock, stratification ratio (concentration in 0–5 to 10–20‐cm layer) and lability (based on particulate organic matter, POM), relative to conventional tillage or ungrazed ryegrass. A 9‐year‐old experiment was conducted in a southern Brazilian Ferralsol. Soil under no‐tillage accumulated 1.11 Mg C ha−1 year−1 and 0.10 Mg N ha−1 year−1 to 100‐cm depth relative to conventional tillage when ryegrass was not grazed, and also increased the stratification ratio of carbon (1.48 vs. 1.11) and nitrogen (1.66 vs. 1.17). The carbon and nitrogen lability was also greater in no‐tillage soil, as carbon and nitrogen stocks increased proportionally more in sand‐POM than in silt or clay size fractions (carbon lability index = 1.57 vs. 1.00; nitrogen lability index = 1.57 vs. 1.00). Semiquinone concentrations in physical fractions were 4–28% smaller in no‐tillage, suggesting less organic matter aromaticity in this treatment. Grazing, however, caused no further improvement of stocks of carbon and nitrogen in the 0–100‐cm layer of no‐tillage soil (e.g., 209 vs. 212 Mg C ha−1, ns), or enhancement of stratification or lability of those elements, relative to ungrazed ryegrass. Overall, no‐tillage effectively promoted soil carbon and nitrogen accumulation and lability in this subtropical Ferralsol, whereas grazing did not compromise the gains of no‐tillage. Highlights: Capacity of no‐tillage and grazing to enhance stocks, stratification and lability of soil C and N.C sequestration with no‐tillage is being debated, and little is known when combined with grazing.No‐tillage accumulated 1.11 Mg C ha−1 year−1 but grazing promoted no further C accumulation.No‐tillage effectively accumulated C in soil and grazing did not compromise such gain of no‐tillage. [ABSTRACT FROM AUTHOR]

Manure application and no‐till management improve soil quality, crop yields and C inputs, but little specific knowledge is available regarding the combined effect of long‐term dairy liquid manure (DLM) application and no‐till management on soil organic matter status and soil structure in topsoils. Here, we assess the impacts of surface‐applied DLM for a 10‐year period on soil total organic carbon (TOC) and nitrogen (TN) concentrations and stocks, on organic matter fractions and on soil physical‐structural attributes in a no‐till crop rotation system on clayey Ferralsol under no‐till crop rotation management in a subtropical climate. Four rates of DLM (0, 60, 120 and 180 m3 ha−1 year−1) were applied in a randomized block design with four replications. Soil samples were collected to calculate TOC and TN stocks to 100‐cm depth and organic matter fractions in the 0–5‐cm layer, and physical indicators of soil quality: bulk density, macroporosity and microporosity and aggregate stability. The largest DLM rates (120 and 180 m3 ha−1 year−1) added 3.8–5.8 Mg C ha−1 year−1 as manure, increased crop residue input by 0.6 Mg C ha−1 year−1, and increased TOC stock by 17% and TN stock by 27% in the top 10 cm of soil, at annual accumulation rates that averaged 0.72 Mg C ha−1 year−1 and 86 kg N ha−1 year−1. Stocks of TOC and TN in the sand‐POM (particulate organic matter) fraction under the 180 m3 ha−1 year−1 rate increased by 49 and 63%, and in the silt‐MOM (mineral‐associated organic matter) fraction by 30 and 47%, respectively. In the clay‐MOM fraction, the change in TOC was not significant, but the TN increased by 16%. Soil physical‐structural attributes (bulk density, porosity and aggregates) were improved by DLM application in the 10‐cm layer and followed the soil carbon and nitrogen increments. Overall, the DLM amendment applied on the soil surface of no‐till proved to be a strategy to ameliorate soil organic matter status, an important factor for agronomic and environmental benefits, besides improving crop biomass production. Highlights: Long‐term application of liquid manure increased concentration and stock of SOC and TN in the 0–10‐cm layer.Increases of 0.72 Mg C ha−1 year−1 and 86 kg N ha−1 year−1 were observed in the 10‐cm topsoil with manure.SOC and TN increased in the sand‐POM and silt‐MOM size fractions but not the clay‐MOM fraction.Improvements to soil physical‐structural attributes were related to organic matter changes. [ABSTRACT FROM AUTHOR]

Evidence is accumulating that belowground crop residues contribute more efficiently to the build‐up and maintenance of native soil organic carbon (SOC) than aboveground plant parts. We corroborated previous testing of the hypothesis that root‐C would preferentially accumulate in soil microaggregates, where it is physically protected against microbially mediated decomposition. In three European field trials with C3 to C4 crop transitions, we compared the content of maize‐C (Zea mays L.) in soil from rotations with grain maize (MG) or silage maize (MS) (i.e. with incorporation of roots and shoots or roots only). After decades of maize cultivation, SOC content did not differ within three out of four MG–MS pairs, although obviously larger amounts of shoot biomass were added to soil in the case of MG. We found that relative contribution of roots was on average 3.5 times more than shoots to the build‐up of SOC per equivalent mass of residue C added to soils. Preferential occlusion of root‐C as silt‐sized intra‐microaggregate particulate organic matter (iPOM) was not observed. There were much larger effects from shoot incorporation on maize‐C in the >53‐μm fraction and free silt and clay. Storage of root‐C as sand‐sized iPOM was not quantified here, but first estimates suggested that physical entrapment at this level could only partly explain the longevity of root‐C in soil. We reconfirm the relative stability of root‐C in soil, but do not conclude that this stems from preferential physical entrapment over shoot‐C. Future work should investigate the cause of preferential root‐C association with the clay‐sized fraction and if this occurs before or after microbial processing. Highlights: The hypothesized preferential physical stabilization of root‐C was assessed.Aboveground biomass had a minor effect on SOC storage in European long‐term trials.Contribution of maize root‐C to maintenance of SOC was three‐fold that of shoot‐C inputs.There was no preferential occlusion of root‐C in silt‐sized microaggregates. [ABSTRACT FROM AUTHOR]