Estimating shoot to root ratios and annual carbon inputs in soils for cereal crops

Abstract Annual plant C input to soil is one of the major factors determining the quantity of soil organic matter in agroecosystems, and is consequently an important driving variable in soil organic matter simulation models. The aim of this study was to determine the shoot:root (S:R) ratios for different cereal species and cultivars at maturity in order to estimate the annual C inputs. Root biomass measurements were made for selected cereal species and cultivars at two sites in eastern Canada (Ottawa, Ontario and Quebec, Quebec). Soil cores were taken at two depths (0–15 and 15–30 cm) and at three positions: within the row (WR), between rows (BR) and in an intermediate position (IP). Approximately 70% of the total root biomass measured was recovered in the 0–15-cm layer. Large differences existed in S:R ratios between the cereal species, the average S:R ratio for winter wheat (4.9) at the Ottawa site being significantly higher than those for oats and barley (2.5 and 2.0, respectively). There were no statistically significant differences in the root biomass produced or in S:R ratios among cultivars for a given cereal species. Assuming that 50% of the total amount of C allocated below-ground is released as extra-root C, the estimated annual C inputs to the soil for cereal crops in Quebec varied from 182–279 g m−2 without straw removal, and from 114–205 g m−2 with straw removal. Although these estimates are within the range of values reported in the literature, further studies are still needed to improve their accuracy for C modeling purposes.

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