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Importance of Crop Drive-Rows for Soil Carbon Storage in Woody Perennial Crops - Andrew Midwood, UBC Okanagan

Soils hold large amounts of carbon (C), and have the potential to influence atmospheric CO2 levels. As a consequence of this, considerable research efforts are currently focused on identifying farming practices that increase soil C levels. This is an attractive goal since it can lead to a reduction in atmospheric CO2, and at the same time improve soil quality, through better water holding capacity, nutrient availability and textural properties. Here we discuss a regional project which involved sampling over 80 apple, cherry and vineyard sites along the Okanagan Valley from Osoyoos to Vernon. We set out to investigate the impact of irrigation on C stored in soils in orchards and vineyards. Overall, concentrations of soil C were highest in cherry orchards, intermediate in apple orchards, and lowest in vineyards. Across all these cropping systems, our work has shown that the soils in the drive rows between the crops have more C in them than the irrigated soils by the crops themselves. Our analysis suggests this C is associated with recently assimilated C and probably comes from shallow rooted grasses and cover crops, together with inputs from pruning debris and litter. By careful management and a better understanding of how C cycles through these systems, the drive rows might be used to deliberately capture atmospheric CO2, helping reduce the impacts of climate change and at the same time, improve soil quality and increase crop yields.

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Importance of Crop Drive-Rows for Soil Carbon Storage in Woody Perennial Crops - Andrew Midwood, UBC Okanagan

  1. 1. Importance of crop drive-rows for soil carbon storage in woody perennial crops: a regional study Andrew J Midwood1, Kirsten D. Hannam2, Tom Forge2, Denise Neilsen2 and Melanie D Jones1 1Department of Biology, University of British Columbia – Okanagan, Kelowna, BC 2Agriculture and Agri-Food Canada, Summerland, BC
  2. 2. Soils and climate change
  3. 3. Scharlemann, et al. (2014) Soil Organic Carbon (C) Globally, soils are estimated to contain 2,400 gigatons organic carbon (GtC) to a depth of 2 m What is a gigatonne = a billion tonnes, 1012 kg or the weight of 400,000 Olympic Pools
  4. 4. IPCC, 2013 Global Carbon Cycle Small changes to this huge C pool can have a significant impact on the global C cycle, and in particular influence the amount of C in the atmosphere
  5. 5. Soil Organic Carbon • Significant research efforts have focused on soil organic carbon (C) • Goal to find management practices which increase soil C = Improves soil quality, structure, water holding, better nutrient cycling, increase biodiversity and crop yield = Lock away C from the atmosphere for many years WIN – WIN Scenario
  6. 6. Irrigation, Food Production and Soil C • Essential for food production and is increasing • Globally over the last 60 yrs increased from 160 to 325 million ha (FAO, 2017) • In 2016, Canada used 2 billion m3 irrigation water • Increases the range of crops grown and yield • Drives changes in soil properties: SOIL C ?
  7. 7. British Columbia USA Canada Study Area Experimental Design Sampled over 80 sites along the Okanagan Valley 24 - Vineyards (drip line) 17 - Apple orchards (drip line) 19 - Apple orchards (micro-spray) 21 - Cherry orchards (micro-spray)
  8. 8. Methods • Sites covered a range of different soil types and textures from sandy loams to clay rich soils • Soils sampled to 3 depths, 0-15, 15-30 and 30-60 cm • Samples taken from the drive and crop rows • Measured soil bulk density • Analysed the organic C and 13C stable isotope content
  9. 9. Results Drive Row Crop Row 0-15 15-30 30-60 Depth(cm) 0 1 2 30 1 2 3 0-15 15-30 30-60 Depth(cm) Total Organic Carbon Apple Drip Apple Micro- Spray Grape Drip Cherry Micro- Spray (%)
  10. 10. Drive rowCrop row Decreasingsoilorganiccarbon Drive row vegetation Crop: vines, apples or cherries Pruning debris C Dwarfing root stocks Exudate C Root Root C from death/turnover Bare soil surface
  11. 11. Carbon Isotope Analysis 0-15 15-30 30-60 Depth(cm) -24 -23 -22 -21 -20-24 -23 -22 -21 -20 0-15 15-30 30-60 Depth(cm) Organic Carbon d13CV-PDB (‰) Apple Drip Apple Micro- spray Grape Drip Cherry Micro- spray Drive Row Crop Row Plant C = 𝛿13C 24-28 (‰)
  12. 12. Carbon Stock • Using bulk density and C concentration measurements allows the C stock to be estimated (0-30 cm) Cropping system Drive Row (Mg C/ha) Crop Row (Mg C/ha) *Overall (Mg C/ha) Apple Micro-spray 72 57 64 Apple Drip 79 56 67 Apple Average 75 56 66 Grapes Drip 51 43 48 Cherries Micro-spray 73 67 70 *50% land area is devoted to drive rows in apples and cherries, in grapes 60% is drive row
  13. 13. Land Area changes in the Okanagan Valley - 1278 ha + 498 ha + 1141 ha Total change +361 ha 4.30 3.02 1.07 1.57 2.77 3.91 0 2 4 6 8 10 2006 2015 LandArea(kha) Years Changes in Crop Land Area Apples Cherries Grapes Based on data provided Agriculture and Agri-food Canada, Summerland
  14. 14. 0 50 100 150 200 250 300 350 2006 2015 2006 2015 CStock(GgC) Years Soil C Stock Changes Apples Cherries Grapes Crop Row Drive Row Regional C stocks 50% land area is devoted to drive rows in apples and cherries, in grapes 60% is drive row
  15. 15. Changes in regional C stock with different drive row management or crop 1.3 22.9 -12.6 16.6 -21.5 -30 -20 -10 0 10 20 30 Cherries Grapes Apples Cherries Grapes %Change All drive rows managed like Apple All 8500 ha of available land used for a single crop Changes relative to 2015 C stock of 497 Gg C Changes relative to current values
  16. 16. So does irrigation increase soil C? • Combination of plants and irrigation leads to changes in soil C content • Soil C levels are greater under cherry orchards, then apples or grapes • Drive row vegetation and root inputs make significant contributions to soil C
  17. 17. A word of caution about soils and atmospheric CO2 levels • Increasing C sequestration in soils through management of drive row vegetation is beneficial…BUT • Soils have a finite ability to retained C • Soil aggregates, created by the interaction of soil organic C with minerals, provide a protective environment for C rich molecules • Protection of C within aggregates is a key factor in how long C will be retained within the soil profile • Some soils are better than others – degree of C saturation
  18. 18. Next steps • Dig into question of C persistence in soils of the Okanagan Valley • Use size fractionation to quantify mineral associate organic C • Use 13C isotope analysis of these fractions to help track the relative proportions of newly added C to older C • Build our understanding of the C sequestration capacity of the soils in this region
  19. 19. Soils are only part of the answer • Soils finite capacity to retain C and the access to managed land globally, will limit the impact soils can make on rising atmospheric CO2 levels • That said, it remains essential we protect soil C and adopt management practices which increase it, securing food production for the future. • Exploit the win-win!
  20. 20. Acknowledgements Our work is funded by Agriculture and Agri-Food Canada, Agricultural Greenhouse Gases Program. Thanks to orchardists and vineyard managers of the Okanagan valley for letting us sample their soils Field and lab assistance: Tirhas Gebretsadikan, Naomi Yamaoka, Ieva Zigg and Sophia Russo. Allyson Dyck, Maya Bandy, Paige Munro, Shawn Kuchta, Brayden Jones, Istvan Losso, Seanna Zintel and Elaine Wong.
  21. 21. Soils and climate change