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Agricultural grass cultivars bred for increased forage yield commonly have extensive root systems. As roots are an important input of organic matter into the soil, it follows that such cultivars could lead to important increases in soil organic carbon (SOC), but this, and the mechanisms involved, are poorly understood with little empirical field evidence. We assessed the effect of two cultivars, Lolium perenne L. cv. "AberMagic" and L. perenne L. × Festuca pratensis Huds. cv. "Prior", in comparison with mixed‐species permanent pasture ("Pasture") in a field experiment on temperate alluvial soil in the southwest UK. Root and SOC stocks, and specific plant‐derived lipids as mechanistic biomarkers for shoot and root inputs of C, were measured on intact 1‐m volumetric soil cores collected on four dates in 2013–2015. Total grass yields were greater for both grass cultivars (40–43 Mg ha−1) than Pasture (39 Mg ha−1), and by 2015 root stocks in the upper 0.1 m were significantly greater by more than 4.7 Mg ha−1. At 0.1–0.3 m depth, SOC stocks (per 0.1‐m depth) were significantly greater under the two grass cultivars (24–50 Mg ha−1) compared to Pasture (18–32 Mg ha−1). In the full 1‐m profile, mean SOC stocks were 137, 133 and 110 Mg ha−1 for AberMagic, Prior and Pasture, respectively, matching root biomass distribution. Odd‐chain n‐alkane concentrations were significantly greater for shoots than roots (274 vs. 64 mg kg−1, respectively), and roots had significantly greater concentrations than shoots of even‐chain hydroxy fatty acids (1829 vs. 305 mg kg−1, respectively) and diacids (317 vs. 93 mg kg−1, respectively). This confirmed lipids as candidate biomarkers for distinguishing shoot and root inputs into the soil, with roots being the dominant source of SOC. Based on the observations of increased forage yield and SOC stock, high‐yielding forage grass cultivars can contribute to future strategies for climate‐smart agriculture in grassland‐dominated temperate regions. Highlights: Selected root traits for increased depth, density and diameter may increase SOC in grassland.The effect of two high‐yielding forage grass cultivars were assessed in a field trial.Fast‐growing, high‐yielding cultivars enhanced root and SOC stocks compared to typical pasture.Lipid biomarkers confirmed that root inputs were the predominant C input to soil. [ABSTRACT FROM AUTHOR]

Reduced use of fossil energy by removing cereal straw for bioenergy potentially threatens soil organic carbon (SOC) storage. Straw incorporation plays a key role for SOC storage in cereal‐based cropping systems, but the use of cover crops (CCs) may compensate for straw removal. However, assessing the SOC sequestration potential of management changes requires field experiments with long continued treatments and frequent soil sampling. Based on a field experiment initiated in 1981 on a sandy loam soil at Askov Experimental Station (Denmark), we examined the effect of annual additions of spring barley straw (0, 4, 8 and 12 Mg ha−1) and undersown ryegrass CC on SOC storage in the 0‐ to 20‐cm layer. The effect of straw incorporation and CC on SOC was additive. At steady‐state conditions, the SOC stock based on equivalent soil mass (SOC stockFM) increased 3.9, 6.7 and 9.3 Mg C ha−1 after annual incorporation of 4, 8 and 12 Mg straw ha−1, respectively. The ryegrass CC increased SOC stockFM by 3.3 Mg C ha−1 and thus almost compensated for removal of 4 Mg straw ha−1. An asymptotic regression model best described the temporal changes in SOC and showed that the effect of straw incorporation and ryegrass CC on SOC sequestration peaks after 10–15 years when a new equilibrium between input and output of C is reached. Clearly, reliable assessments of SOC sequestration potentials following changes in management require field experiments with frequent soil sampling until reaching steady‐state conditions. Highlights: SOC sequestration potentials of straw incorporation and CCs were assessed.The crucial issue of sequestration duration of experimental treatments is often neglected.The effect of straw and CC peaked after 10–15 years when a new equilibrium in SOC was reached.Reliable assessments require frequent soil sampling until reaching steady‐state conditions. [ABSTRACT FROM AUTHOR]

Nitrogen (N) fertilization is the major contributor to nitrous oxide (N2O) emissions from agricultural soil, especially in post‐harvest seasons. This study was carried out to investigate whether ryegrass serving as cover crop affects soil N2O emissions and denitrifier community size. A microcosm experiment was conducted with soil planted with perennial ryegrass (Lolium perenne L.) and bare soil, each with four levels of N fertilizer (0, 5, 10 and 20 g N m−2; applied as calcium ammonium nitrate). The closed‐chamber approach was used to measure soil N2O fluxes. Real‐time PCR was used to estimate the biomass of bacteria and fungi and the abundance of genes involved in denitrification in soil. The results showed that the presence of ryegrass decreased the nitrate content in soil. Cumulative N2O emissions of soil with grass were lower than in bare soil at 5 and 10 g N m−2. Fertilization levels did not affect the abundance of soil bacteria and fungi. Soil with grass showed greater abundances of bacteria and fungi, as well as microorganisms carrying narG, napA, nirK, nirS and nosZ clade I genes. It is concluded that ryegrass serving as a cover crop holds the potential to mitigate soil N2O emissions in soils with moderate or high NO3− concentrations. This highlights the importance of cover crops for the reduction of N2O emissions from soil, particularly following N fertilization. Future research should explore the full potential of ryegrass to reduce soil N2O emissions under field conditions as well as in different soils. Highlights: This study was to investigate whether ryegrass serving as cover crop affects soil N2O emissions and denitrifier community size;Plant reduced soil N substrates on one side, but their root exudates stimulated denitrification on the other side;N2O emissions were lower in soil with grass than bare soil at medium fertilizer levels, and growing grass stimulated the proliferation of almost all the denitrifying bacteria except nosZ clade II;Ryegrass serving as a cover crop holds the potential to mitigate soil N2O emissions. [ABSTRACT FROM AUTHOR]

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]

The effect of different earthworm functional groups on the incorporation of maize (C4 plant) dung into a soil (C3 organic matter background) sown with ryegrass (C3 plant) was explored by using differences in the carbon (C) isotope ratios (12C and 13C) between plant and soil samples in a field mesocosm study. The abundance of earthworms increased with dung inputs, reaching over 4000 earthworms per m², presumably because of the increased food resources used. The amount of dung C incorporated into the soil profile in the presence of earthworms was dependent on the amount of organicmatter deposited on the soil surface (925-4620 g Cm-2) and reached rates of 1200 g Cm-2 annually in the treatment receiving repeat dung applications. Dung incorporation was largely concentrated in the surface 0-75 mm, although small amounts of dung-derived C were observed to a depth of 300 mm. This was especially so in the presence of anecic earthworms, equating to an extra 70 g Cm-2 annually for the 150-300 mm depth increment. It is important to note, in calculating C incorporation rates from earthworms, that only 10-20% of the soil surface in grazed pastures is covered by dung. After 444 days, less than 32% of the applied dung was detected within the upper 300mm of the soil profile. This study emphasized the need for all three earthworm functional groups to be present within the soil in order to maximize the amount of surface dung that could be incorporated into soil organic matter. [ABSTRACT FROM AUTHOR]