This document discusses the importance of soil organic matter (SOM) for soil health and resilience. It summarizes several studies that found soil carbon levels were higher in rotations that included perennial forages. An example 3-year crop rotation of winter wheat over-seeded with red clover, soybeans, and corn is provided. Benefits of red clover for soils are outlined, such as increasing microbial activity, aggregate stability, and soil organic matter. Maintaining SOM through practices like cover crops and maintaining crop residues is important for sustaining soil productivity.

1.
Linking Soil Quality to
Economic Incentives
Ralph C. Martin, Ph.D., P.Ag.
Loblaw Chair, Sustainable Food Production
Tel: 519-­‐824-­‐4120, Ext 52460
Email: rcmartin@uoguelph.ca

2. Soil Organic Matter (SOM) is good,
good, good
SOM is added with green manures, brown
manures and crop residues
SOM helps to bind soil particles into good soil
structure
SOM matter allows
infiltration
SOM provides resilience
during droughts, floods
and extreme conditions

3. Soil Carbon
A. Nelson (M.Sc. Thesis -­‐ U. of M.)
Rotation had largest effect on soil carbon;
soil carbon higher in rotations including perennial
forages, regardless of organic or conventional
management

4. Ontario 3-­‐Year Crop Rotation
www.southernsare.org; www.uoguelph.ca; www. Scientificamerican.com
Winter wheat over-seeded with red clover
Soybean Corn
Year
One
Year TwoYear
Three

5. Red Clover Benefits for Soils
Increases
Microbial Activity
Sources: Lupwayi et. al , 1998; Snapp et. al, 2005; Queen et. al, 2009; Blaser et. al, 2011
Increases
Aggregate
Stability
Improves Water
Holding Capacity
Erosion
Prevention Increases Soil
Organic Matter
Decreases Soil
Compaction
Builds Soil Tilth
Photo: Amélie Gaudin
Gaudin

6. Biological Infrastructure of Agriculture
Well managed forages
provide cost effective feed,
soil cover, C, nutrients +
Grasses for biomass sales,
soil cover, C and nutrients +
Cover crops are soil builders,
soil cover, C and nutrients +
Should governments support
biological infrastructure?

7. Wheat Straw and Corn Stalks
If remove crop residues
from arable land for
bio-­‐products and
bio-­‐fuel,
then crucial to maintain
SOM with soil builders,
with and between cash
crops.

8. Possible Accounting
1) NMP include C balance
(inputs removal) to
show if SOM is declining
or improving?
2) Can SOM be measured cost effectively and
accurately enough, every 5 years, on each field?
3) Crop insurance fees might decrease if SOM
levels increase, or vice-­‐versa

9. 9
White Elephant of N
About 48% (and rising) of people depend directly
on the Haber-­‐Bosch process for basic food
Excess N losses to water (NO3) and air (N2O).
N fertilizer is one-­‐third of global agricultural energy
budget and related GHG emissions

10. 10
Use N Efficiently
-­‐ Legumes, cover & catch crops
-­‐ Recycle manure, MSW,
AD digestate and sewage
-­‐ Organic Ag
-­‐ Deen -­‐ Maximum Economic N Rate (MERN) for corn starts
to level off at 100 kg N/ha and, after clover, at 50 kg N/ha;
for next 100 kg N/ha, MERN ranges from $ 0 -­‐ $25/ ha
-­‐ Calculate MERN for each crop, in NMP.
Only N fertilizer, up to lowest range of MERN, eligible as a
tax deductible expense?
-­‐ Reduce food waste

11. Soil Renewal Rate
To form a 2.5 cm depth of soil (340 t/ha)
requires 200 to 1000 years, a renewal
rate of 0.3 to 2 t/ha/yr
In U.S.A., soil erosion averages 18 t/ha/yr
(Pimental et al. 1987. Bioscience 37:277-­‐283)

12. Productivity of eroded soil
Productivity of eroded soils
will decline even if fertilizer is
added (Brady and Weil 2002, Fig 17.8)
or if the eroded soil
is irrigated (Larney
et al. 1995 J. Soil Water
Conserv. 50:87-­‐91)

13. The Revised Universal Soil Loss Equation
(RUSLE) = RKLSCP
R = rainfall erosivity
K = soil erodabality
LS = length and
steepness of slope
C = cover and crop
management
P = practices of erosion control
(Brady and Weil 2002, 754 -­‐ 763)

14. Observing and Caring
Erosion control practices tend to
increase on farms:
1) with farmers mostly on the farm
2) organized as family units
(Wall et al. 2002)

15. Attitude of Gratitude
Take moments to be
thankful, especially for
healthy soil and food.
Appreciate what we
have and treasure it.

16. Vision to Sustain Food
A food system, based on healthy
soil, clean air and water, minimal
waste and regenerative energy,
to support profitable and resilient
farming and fishing communities and
a healthy food supply for all.
rcmartin@uoguelph.ca