Importance of drive-row vegetation for soil carbon storage in woody perennial crops: A regional study
Midwood, A.J., Hannam, K.D., Forge, T.A., Neilsen, D., Emde, D., Jones, M.D. (2020). Importance of drive-row vegetation for soil carbon storage in woody perennial crops: A regional study. Geoderma, [online] 377 http://dx.doi.org/10.1016/j.geoderma.2020.114591
Plain language summary
Soils store large amounts of organic carbon. Soil organic carbon (SOC) is formed primarily from decomposing plant leaves and roots. Careful soil management can increase SOC, which improves soil quality and slows the release of carbon dioxide into the atmosphere. The objective of the study was to determine whether Okanagan Valley, BC, apple orchards, cherry orchards or vineyards store the most SOC. SOC was measured in soil samples collected to 60 cm depth in 25 cherry orchards, 36 apple orchards and 24 vineyards distributed across the Okanagan Valley. SOC was consistently higher in un-managed drive rows than in crop rows, where fruit trees or grapevines are cultivated. This is probably because grasses and herbaceous weeds usually cover the soil surface of drive rows; the C-rich roots and leaves of these plants add to the SOC pool. By contrast, the soil surface in crop rows is usually kept bare and, as a result, there are fewer plant inputs into the soil. Overall, cherry orchards had higher SOC contents (70 Mg C/ha) than apple orchards (66 Mg C/ha) or vineyards (48 Mg C/ha). If all orchards and vineyards in the Okanagan Valley were managed as a typical cherry orchard, an estimated 596 Gg of additional SOC could be stored. This work demonstrates that agricultural practices could be harnessed to increase the amount of SOC stored in the soil and help slow the rate of climate change by slowing the release of carbon dioxide into the atmosphere.
Increasing the carbon (C) content of agricultural soils can help mitigate rising atmospheric CO2 concentrations, improve soil health and increase crop yield. Unlike annual cropping systems, soils planted to perennial woody crops, such as vineyards and orchards, are left undisturbed for many years making them particularly amenable to soil C storage. Here, we used a regional sampling campaign of over 80 commercially-managed sites across the Okanagan Valley, in the southern interior of British Columbia, Canada, to examine the spatial distribution of soil C under irrigated perennial woody crops. Using this living lab approach, we collected soils from the crop and drive rows of apple and cherry orchards, and vineyards subjected to a wide range of real-life management regimes (e.g., for weed and pest control, fertilizer application, etc.). Sites were selected with soils belonging to five surficial deposit classes, representing 40% of the mapped agricultural land area. Soil C was spatially heterogeneous across all the sites, with the surface soil (0–15 cm) of drive rows containing more C than the soil in adjacent crop rows. Clear differences emerged among cropping systems, despite the variation in management practices applied by individual growers. Drip-irrigated apple orchards showed the greatest spatial heterogeneity, with C concentrations of 2.9% in the drive row and 1.8% in the crop row, while vineyard and cherry orchard soils showed the least, with differences between crop and drive rows of approximately 0.3%. Higher C concentrations in the drive rows appeared to be the result of recently assimilated/less processed litter and fine root C inputs from the shallow-rooted understory vegetation. This was confirmed using stable isotope analysis: drive row soil C was significantly 13C depleted compared to the crop row soil, to a depth of 30 cm. Overall, cherry orchards contained the most C (70 Mg C ha−1 to a depth of 30 cm), vineyards the least (48 Mg C ha−1), and apple orchards were intermediate (66 Mg C ha−1). A recent land-use survey in 2015 determined that 8501 ha of agricultural land in the Okanagan Valley was planted to apples, cherries or grapes, and that large shifts in crop land area have occurred since the previous survey, conducted in 2006. We estimate that apple orchards currently hold approximately 199 Gg C, vineyards 188 Gg C and cherry orchards 110 Gg C. Marked differences in soil C storage between the cropping systems, despite the fact some were less than 10 years old, suggests that soils in this region are responsive to changes in crop and associated management practices over relatively short time periods. We conclude that the drive rows of vineyards offer the greatest scope for increased soil C storage among woody perennial horticultural cropping systems in the Okanagan Valley but that ‘long-term’ soil carbon storage may not be possible in these soils.