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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]

Biochars are widely applied to improve soil pore structures. However, the quantitative effects of biochars on soil macropore networks still remain unclear. In this study, the effects and possible mechanism of biochar application on soil macropore networks were investigated quantitatively by industrial X‐ray microtomography (CT), a pore network model and network analyses. Soil cores of 5 cm in diameter and 10 cm in height were collected from a paddy soil (Typic Haplustalf) without biochar application (CK), and amended with rice straw biochar (RSB), corn straw biochar (CSB) and bamboo biochar (BB) at a rate of 25 Mg ha−1 (w/w). Results revealed that the total and connected macroporosity of the biochar‐amended soil was reduced significantly compared with CK, whereas the reverse was true for the isolated porosity. The three types of biochars exhibited different effects on macropores of the soil, depending on their size and shape. The pore network model and network analyses showed that the physical and topological structures of macropore networks in biochar‐amended soil were clearly reconfigured. The accessibility of these macropore networks was markedly reduced. Our results indicated that the incorporation of biochar did not necessarily increase the soil's macroporosity. The combination of pore network model and network analyses was effective for quantifying key properties of soil macropore networks affected by the incorporation of biochar. The changes in these properties may be used to evaluate the effects of biochar on water, air and nutrient transport. Highlights: Effect of biochars on the soil macropore structure was studied by industrial CT.Macropore network structure was quantified by a pore network model and network analyses.Biochar incorporation markedly changed the accessibility of the soil macropore network.The macropore network of soil can be reconfigured following biochar addition. [ABSTRACT FROM AUTHOR]

Estimation of belowground net primary production ( BNPP) is crucial for prediction of grassland soil organic carbon sequestration, but there are high coefficients of variation ( CV) among methods of estimation. We compared accuracy and precision of two variations of the traditional soil core method and three of the ingrowth core method, over 2 years on grass-white clover swards in Germany. The ingrowth core method (5- to 9-week ingrowth period) provided the most accurate BNPP estimate (471 g m−2) with the highest precision ( CV: 31%), whereas the two soil core approaches resulted in underestimation and high error. Comparing results with other grassland studies, we found that reliability of the ingrowth core method was influenced by ingrowth period and sward rooting pattern related to grass phenological stages, while the precision was determined by ingrowth period and grassland productivity. We therefore recommend using the ingrowth core method for managed grasslands where belowground productivity is relatively high and installation disturbance is likely to be negligible. Using a 6- to 8-week ingrowth period, the method delivers reliable and feasible BNPP estimates for temperate managed grasslands which can be applied to long-term soil carbon budget simulation. Results from our work and other studies also indicated that standing root biomass masks seasonal pattern of rooting due to synchrony between root birth and death. The soil core method is likely to lead to underestimates and higher errors than the ingrowth core methods and thus should be avoided. [ABSTRACT FROM AUTHOR]

Root systems are important for global models of below-ground carbon and nutrient cycling. Notoriously difficult sampling methods and the fractal distribution of root diameters in the soil make data being used in these models especially susceptible to error resulting from under-sampling. We applied the concept of species accumulation curves to root data to quantify the extent of under-sampling inherent to minirhizotron and soil coring sampling for both root uptake and carbon content studies. Based on differences in sample size alone, minirhizotron sampling missed approximately one third of the root diameters observed by soil core sampling. Sample volumes needed to encounter 90% of root diameters averaged 2481 cm3 for uptake studies and 5878 cm3 for root carbon content studies. These results show that small sample volumes encounter a non-representative sample of the overall root pool, and provide future guidelines for determining optimal sample volumes in root studies. [ABSTRACT FROM AUTHOR]

1 Elucidation of the patterns and controls of forest net primary production at ecosystem scales has been hindered by a poor understanding of fine root production, due largely to technical limitations. 2 Fine root (≤ 0.5 mm diameter) production was assessed using minirhizotron, soil core, ingrowth core, nitrogen budget and carbon budget techniques in three longleaf pine-wiregrass forest ecosystem types (hydric, mesic and xeric) forming an edaphic resource availability and above-ground productivity gradient. 3 Fine root production estimates differed substantially in magnitude, e.g. values ranged from 0 to 4618 kg ha−1 year−1 for the soil core and minirhizotron techniques, respectively, in the hydric site. 4 Minirhizotron production estimates in the hydric, mesic and xeric sites were 4618, 1905 and 2295 kg ha−1 year−1, respectively. 5 Soil core and ingrowth core root production estimates were on average 81 and 54% lower, respectively, than corresponding minirhizotron production estimates, and minirhizotron estimates were negatively related to soil core and ingrowth core estimates across the resource gradient. 6 The N budget method yielded unreliable root production estimates, presumably due to the underestimation of N availability for plant assimilation. 7 C budget estimates of total below-ground C allocation (6773, 5646 and 4647 kg C ha−1 year−1) were positively related to minirhizotron production estimates, but negatively related to soil core and ingrowth core production estimates. 8 Critical evaluations of the assumptions, potential errors and results for each method suggest that the minirhizotron technique yielded the most reliable root production estimates, and that the negative relationship between minirhizotron and core-based estimates may be attributed to the inherent deficiency of the core techniques in assessing root production when mortality and production occur simultaneously. 9 Minirhizotron root production estimates were positively related to foliage production estimates, supporting the hypothesis of constant proportional allocation of production to foliage, wood and fine roots across resource availability gradients in temperate forests. 10 These results suggest that fine root production is not negatively correlated with soil resource availability and foliage production as is commonly perceived in the ecological community and represented in ecosystem computer models. [ABSTRACT FROM AUTHOR]