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.

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. Soils and climate change

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. 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. 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. 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. 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. 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. 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. 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. 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. 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. 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. 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. 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. 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. 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. 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. 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. 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.

22. Soils and climate change