Assessing Soil Health: Building Resilience Following a Wet Harvest............................... Marla Riekman, PAg, CCA Soil Management Specialist Manitoba Agriculture
SOIL HEALTH PHYSICAL Soil compaction Water infiltration Aggregates ORGANIC MATTER/ AGGREGATE STABILITY CHEMICAL ph Potassium Phosphorus Ca, Zn, Mg, Mn............................... BIOLOGICAL Potentially mineralizable N % Organic Matter Respiration
Soil Health Defined as "the continued capacity of soil to function as a vital living system, within ecosystem and land-use boundaries, to sustain biological productivity, promote the quality of air and water environments, and maintain plant, animal, and human health" (Pankhurst et al., 1997).
Soil Quality How well soil does what we want it to do Regulates water Sustains plant and animal life Filters potential pollutants Cycles nutrients Supports structures
Soil Quality Parameters Chemical: Soil Organic Matter (SOM); ph; Electrical Conductivity (EC); Extractable Nutrients Physical: Soil Structure; Depth of Soil; Infiltration; Bulk Density; Water Holding Capacity Biological: Microbial Biomass C and N; Potentially Mineralizable N, Soil Respiration
Soil Quality Parameters Chemical: Soil Organic Matter (SOM); ph; Electrical Conductivity (EC); Extractable Nutrients Physical: Soil Structure; Depth of Soil; Infiltration; Bulk Density; Water Holding Capacity Biological: Microbial Biomass C and N; Potentially Mineralizable N, Soil Respiration
SOIL COMPACTION
Soil moisture affects compaction When soil is dry Sufficient soil strength to resist compaction With extremely wet soil All pores are water filled and soils cannot be compacted since shear strength is near zero Causes large, deep, muddy ruts with little or no compaction
Soil moisture affects compaction Be careful when soil is moist!! Aggregates become lubricated with water and reduce shear strength Large pores are air-filled, smaller pores water filled. With pressure, large pores collapse, resulting in compaction Greatest compaction occurs near field capacity
Approximate axle loads for field equipment Equipment Axle Load (tons/axle) Slurry tanker 4,200 gal. 10-12 Slurry tanker 7,200 gal. 17-18 6-row combine, empty 10 12-row combine, empty 18 12-row, full with head 24 720 bu. grain cart, full, 1 axle 22 Beet cart, full 24 Grain cart, 1,200 bu., 1 axle 35-40 Grain cart, 1,200 bu., 2 axle 17-20 4WD tractor, 325 HP, front axle 13 4WD tractor, 200 HP, front axle 7.5 MFWD tractor, 150 HP, rear axle 6.5 From UMinn Extension Factsheet - Soil Compaction: Causes, Effects and Control
About 80% of compaction happens on the FIRST PASS Wheel Traffic Compaction
Grain Yield Effects of weather on crop yield response to compaction level Wet Season Dry Season Compaction adapted from Soane et al., 1994
I don t have to worry too much about soil compaction, Mother Nature will take care of it, won t she????
Slide Courtesy of Jodi dejong-hughes
She does help Freeze/thaw helps break up lumps at the surface where there is multiple freeze/thaw events Deeper soil may freeze only once Wetting/drying is more effective on our prairie soils with clay that shrinks and swells (but for this to work, we need the soil to dry!)
...but we need to do the rest
HOW DO WE BUILD RESILIENCE? With activities that create and/or maintain good soil structure
Building soil resilience Prevent compaction in the first place Check and maintain tire pressure Reduce total axle load Minimize the number of trips over a field Use duals/large diameter tires or tracks Reduce tillage Rotate deep rooted, water-loving crops to decrease soil moisture
Building soil resilience Use cover crops May play an important role in soil drying by increasing length of growing season Manitoba data on berseem clover cover crop increased downward movement of water and reduced soil moisture May allow soil to be trafficked at a higher moisture content without causing compaction
HOW DO WE KNOW IF WE ARE MAKING A DIFFERENCE?
How do we measure Soil Quality? Soil Quality Test Kit (USDA) Measures: Salinity (EC); ph Soil Structure; Aggregate Stability Soil Texture; Bulk Density, Compaction Water Infiltration Soil Respiration Earthworms
Is your soil healthy?
Touch Texture: clay, silt, sand Water holding capacity drainage Structure: aggregates shape and size, compaction Moisture: yield potential
Sight Colour A horizon = black = high organic matter and once was originally nutrient rich Subsoil: Brown = well drained Grey = poorly drained Mottles = imperfectly drained
Eroded landscapes are colour coded
Smell Excess water anaerobic microbes, H 2 S emitted Good, earthy smell = actinomycetes
Microbial changes under soils Aerobic bacteria actinomycetes fungi protoza nematodes arthropods earthworms Dry Moist Flooded Anaerobic bacteria algae
Observe Crop Growth
Indicator weeds acidic soil Devils paintbrush (orange hawkweed)
Indicator weeds low P
Indicator weeds high soil N
Indicator weeds compaction
Indicator weeds salinity
Slake Test Aggregate Stability Test
Solvita Test
Variability across Landscapes
Summary While there are fancy tests available for soil health, you can begin by using your senses to evaluate the soil Touch, Sight, Smell Remember to compare like with like (soil texture) and consider landscape position when sampling
Summary When it comes to managing wet soils at harvest, good soil structure is your best defence Make sure that ANY activity on the field happens when soil conditions are good...but I know this is difficult!!!! When working in less than ideal conditions, try to decrease axle loads and make sure tractor is performing optimally
We need to be deliberate about how we travel on the field during field operations, particularly harvest. This may be more evident when soil is saturated, but just as important when soil is moist.
THANK YOU marla.riekman@gov.mb.ca 204-266-2027 @MBsoilsleuth