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Soil Compaction in Alfalfa Fields Ronald T. Schuler, Professor Extension Agricultural Engineer Biological Systems Engineering University of Wisconsin-Madison Soil Compaction Causes include combinations of: Wheel Traffic Tillage Precipitation Types Surface Subsoil Loam soil by volume
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Soil Compaction in Alfalfa Fields Ronald T. Schuler, Professor Extension Agricultural Engineer Biological Systems Engineering University of Wisconsin-Madison
Soil Compaction • Causes include combinations of: • Wheel Traffic • Tillage • Precipitation • Types • Surface • Subsoil
Loam soil by volume Non-compacted Compacted
Compaction Issues • Tires • Size • Inflation pressure • Tire design, radial vs. bias • Machinery • Avoid wet soil • Wheel alignment • Machine selection • Machine weight
Compaction Issues • Tires • Size • Inflation pressure • Tire design, radial vs. bias • Machinery • Avoid wet soil • Wheel alignment • Machine selection • Machine weight
Contact Area-Size-Diameter(Firestone) Tire Size Tire Dia. Area(in2) Radial TiresFlat 3”Sinkage 18.4R34 65.1 320 720 18.4R38 69.0 340 740 18.4R42 73.0 350 760 18.4R46 77.0 365 780 Bias Tires 18.4-34 65.4 284 653 18.4-38 69.3 300 675
Contact Area-Size-Width(Firestone) Tire Size Tire WidthArea(in2) Radial TiresFlat 3”Sinkage 16.9R38 16.9 255 660 18.4R38 18.4 340 740 20.8R38 20.8 390 870 Bias Tires 16.9-38 16.9 252 629 18.4-38 18.4 300 675
Compaction Issues • Tires • Size • Inflation pressure • Tire design, radial vs. bias • Machinery • Avoid wet soil • Wheel alignment • Machine selection • Machine weight
Impact of Tire Pressure 6 psi 18 psi
Inflation pressure-slight tire bulge with the proper pressure on radial ply tires 6 psi 18 psi Bulge
Top View: Measured soil-tire interface stress (psi) distribution of an 18.4R38 tire
Compaction Issues • Tires • Size • Inflation pressure • Tire design, radial vs. bias ply • Machinery • Avoid wet soil • Wheel alignment • Machine selection • Machine weight
Radial vs. Bias Ply Tires Contact Area
At Proper Inflation Pressure, Radials have greater Contact Area
Tractor Manufacturer RecommendationsTire Size – 18.4-34 Pressures-psi Axle Load (lbs) Radial Bias 5500 6 16 6000 7 16 6500 7 16 7000 8 16 7500 9 16 8000 10 16 8500 12 16 9000 13 16 9500 14 16 10000 15 16
Compaction Issues • Tires • Size • Inflation pressure • Tire design, radial vs. bias • Machinery • Avoid wet soil • Wheel alignment • Machine selection • Machine weight
Impact of soil moisture on compaction(depth and sinkage) 0 4 8 12 16 20 24 28 Hard dry soil Normal Wet soil Depth, In.
Compaction Issues • Tires • Size • Inflation pressure • Tire design, radial vs. bias • Machinery • Avoid wet soil • Wheel alignment • Machine selection • Machine weight
Wheel alignment-harvester and wagon Wheels should follow in same track
Small Square Baler-Bottom FeedWheels aligned-tractor, baler and wagon
Compaction Issues • Tires • Size • Inflation pressure • Tire design, radial vs. bias • Machinery • Avoid wet soil • Wheel alignment • Machine selection • Machine weight
Merger - Picks up one windrow and places it on the adjacent one
1 Mower-conditioner-pull or self-propelled2 Mower conditioner width, feet3 Rake-to rake, merge or do not rake two windrows together4 Area covered by wheel traffic if uniformly distributed5 T-M/A – ton miles per acre System Comparisons-three cuttings per year Type1 Width2 (ft) Rake3 Area4 T-M/A5 Pull 13 None 4.0 50 Pull 16 None 3.4 44 Pull 13 Rake 3.2 35 Pull 16 Rake 2.7 33 Self-Prop 16 Rake 3.1 32 Self-Prop 16 Merge 3.0 32 Pull 13 Merge 3.4 37 Self-Prop 13 Merge(Dbl) 2.8 27 Self-Prop 16 Merge(Dbl) 2.3 32
Compaction Issues • Tires • Size • Inflation pressure • Tire design, radial vs. bias • Machinery • Avoid wet soil • Wheel alignment • Machine selection • Machine weight
Tractor ballasting criteria Towed Load wt. vs. Max.Speed Towing machine wt. mph 1 to 1 20 2 to 1 10 More than 2 to 1 Do not tow
Concluding Remarks • Select appropriate tire • Use proper tire pressure • Align wheels • Reduce traffic of large equipment • Use safe towing machine weight