Agritechnica 2016 Soil Compaction in Grassland John Maher Teagasc, Ireland
600 mm 3000 mm 1300 mm
Monthly Rainfall (mm) in Ireland Grazing Conservation
Why Grazed Grass??? 285 Days of Feed Cost of feed (Energy Basis) 33% Cost of Grass Silage 25% Cost of Concentrate Grazed Grass: High Feed Value Provided it is managed well Cows Feed themselves Avoids harvesting cost Avoids storage cost & Feeding out cost Cows Spread their own Slurry
Soil Type Compact Easily Sand 6% Silt 53% Clay 41% Less Compaction Sand: 46% Silt: 46% Clay 8%
Compaction Causes Animal Traffic Machinery Traffic
Soil Structure + Compaction Structure Arrangement of soil particles and pore spaces between them Critical to all soil functions Compaction Alteration of the soil structure by compressive forces
Threats to structure Increased machine weight Increased intensity of operations Extended grazing season
Directly impedes root growth Compaction effects Influences access to nutrients and water Reduces soil pore space (50% - 30%) Less aeration for biological function (impacts on nutrient cycling: Denitrification) Less inflitration / drainage: Further root growth restriction Reduced uptake of nutrients (water) Reduced plant growth
Practical Impacts Reduced yield (grass or crop). Inefficient use of nutrients Ponding/Water on surface Weed grasses etc. Delayed field operations Machine Grazing
Compaction + Yield Teagasc Research: Yield Reductions Cereals 0 to 20% Maize 0 to 50% Grass 8 to 30%
Compaction Risk Factors Soil type (including OM) Presence or absence of vegetation Soil Moisture Content Machine weight, Ground pressure Traffic density Animal weight + Traffic density
Depth + Duration Shallow (<150 200mm) Frequent in arable cultivation resolves? Frequency in Grassland Deep (>200mm) More difficult to resolve in all soils Persistence of compaction Typically 2 to 7 years Can be longer
Compacted Top-Soil Compacted Sub-Soil
Soil Examination (Visual) Spade extract 300mm undisturbed profile Examine for: Blocky, platy structure vs Crumb structure Horizontal layering vs vertical channels, Pans Earthworms Grey mottling Deep invasive roots
Examine Profile 300mm Spade-full
Preventing Compaction
Land Drainage (Deep Drains 1.8m)
Land Drainage (Shallow Drains 0.8m)
How do we Prevent? Restrict Traffic Animals: Grazing management Field Infrastructure Housing (get animals off when necessary) Breeding for Smaller Cows Machinery: Avoid in wet conditions Reduced loads and Pressures Larger tyres/lower Pressure
GRAZING TECHNIQUES: Grazing from Back Cow Walk Spokes of Wheel Strip-grazing Day 2 pm Day 2 am Day 1 pm Day 1 pm Day 2 am Morning Evening Tomorrow Evening Day 1 am Day 1 am Tomorrow Morning Roadway Farmyard Entry EXIT
Weight 4t 4t 8t Tyres Contact Area Air in tyre supports load Inflation pressure = Ground pressure Large tyres - big volume - low pressure 2.0 bar GP 1.0 bar GP 2.0 bar GP
1.0 bar GP 1.0 bar GP 2t 4t Axle load is important Soil Level 0.5m 100kpa 75kpa 50kpa 25kpa 1.0m
Fixing Compaction
Option 1: Time Allow soils to self repair Shrinking + swelling can help Frosts? (shallow) Must remove compaction cause (if obvious) Inexpensive and avoids doing harm May not be adequate!
Grassland - Aeration Shallow loosening (100-200mm) Spiker Teagasc Research 10 trial sites 3 years, multiple harvests. Some Initial responses (maybe N Mineralisation) No response to routine treatment
Subsoiling / Deep Loosening Loosens by shattering to greater depth 300-400mm Power demanding (45 kw / leg at 400mm) Leg spacing depends on depth and wings With wings = 2 x depth E.g. At 300mm depth: 600mm spacing: 5 legs in 3m Grassland Not suitable for rock / stone
Deep Loosening Effective? Prevention is better than cure Avoid the need for deep loosening Research not clear-cut Some Negative results Some Slightly positive results Little Longterm Benefit Arable research Re-compaction risk is real
Re-compaction risk Loosened soils Loose to depth of subsoiler More moisture through profile Prone to Re- Compaction May compact to deeper depth Shifting problem down even more difficult to solve
Soil Compaction Prevention is Better than Cure!!!
Prevention is better than Cure