Soil Compaction: Soil Compaction: Where, How Bad, What to Do? Where, How Bad, What to Do? • What is compaction? Ken Sudduth • What causes it? Ag Engineer • What are some of the effects? USDA Agricultural Research Service • How can we measure compaction? Columbia, MO • How can we manage compaction? Soil Compaction: Where, How Bad, What to Do? What is Compaction? Compaction is simply a reduction in pore space Thanks to the following for providing some of the slides and data used in this presentation: • Dr. Randy Raper, Ag Engineer, USDA-ARS National Soil Dynamics Lab, Auburn, Alabama • Dr. Peter Motavalli, Associate Professor, Soil, Environmental, and Atmospheric Sciences, University of Missouri Composition of the Soil Volume Compaction Definitions • Bulk density (ρb) = Ms/Vt • Soil compaction – Decrease in soil volume and • Particle density porosity, or increase in soil bulk density, due to mechanical stress on soil, for example, from traffic of (ρs)= Ms/Vs agricultural machinery. Compaction can also occur • Porosity = V /V = f t naturally. 1 - (ρb/ρs) • Surface compaction – compaction that occurs in the surface “plow layer” • Subsoil compaction – compaction that occurs below the plow layer due to a surface load. 1 What Causes Compaction? Causes of Compaction • Vehicle Traffic Vehicle Traffic Vehicle Traffic 60000 50000 40000 30000 20000 Weight, lbs. Weight, 10000 0 1948 2000 Factors in Vehicle Compaction Factors in Vehicle Compaction • Weak soil • Weak soil • Moisture Content Effect • Excessive Loads • Density Effect • Size of Load at the Surface – Ground Pressure 2 Factors in Vehicle Compaction Factors in Vehicle Compaction • Weak soil • Weak soil • Excessive Loads • Excessive Loads • Severity of Load at • Severity of Load at the Surface the Surface • Impact at Depth • Impact at Depth • Repeated Loadings • For equal stress at the surface, larger tires • First pass does 80% of total compaction affect soil to a greater depth • Repeated loadings increase compaction • Vehicles have gotten larger! • Controlled traffic / Autoguidance Causes of Compaction Soil Particle Sizes • Vehicle Traffic • Clay (< 0.002 mm) • Natural Soil Reconsolidation • Silt (0.002 -0.05 mm) • Sand (0.05 - 2 mm) Basketballs, Baseballs, and Marbles Hardpan Profile Sand and Silt Sand and Silt and Clay Topsoil Hardpan Subsoil 3 Causes of Compaction What are Some Effects of Compaction? • Vehicle Traffic 100 • Natural Soil 80 Reconsolidation 60 Poorly-Graded • Well-graded soils 40 Well-Graded more susceptible to Percent Finer 20 0 natural compaction 10 0.1 0.001 than poorly- graded Particle Diameter, mm soils Effects of Compaction Effects of Compaction • Increased Soil Erosion • Increased Soil Erosion • Decreased Infiltration Effects of Compaction Effects of Compaction • Increased Soil Erosion • Increased Soil Erosion • Decreased Infiltration • Decreased Infiltration • Decreased Water Storage • Decreased Water Storage • Reduced N Uptake Subsoiled Compacted Compacted Non-compacted 4 Effects of Compaction Effects of Compaction • Increased Soil Erosion • Increased Soil Erosion • Decreased Infiltration • Decreased Infiltration • Decreased Water Storage • Decreased Water Storage • Reduced N Uptake • Reduced N Uptake • Decreased Root Growth • Decreased Root Growth • REDUCED YIELD Effects of Compaction on Yield Effects of Compaction on Yield Corn Grain Yields, 2000 12.0 Corn Grain Yields, 2000 Not compacted 12.0 Compacted Check Compacted NS Subsoil NS 9.0 9.0 Corn LSD(0.05) Corn grain yield -1 6.0 grain yield 6.0 (Mg ha ) LSD -1 (0.05) (Mg ha ) 3.0 3.0 0.0 0.0 0 3.8 7.6 12.8 061020 Turkey litter (dry Mg ha-1) Poultry litter (dry Mg ha-1) Data collected at MU Bradford Farm (Columbia) by Motavalli et al. Data collected at MU Delta Center (Portageville) by Motavalli et al. Compaction and Site-Specific Management It’s the water ! • What is most often the major • Soil and landscape factors that affect plant water cause of within- availability are often the major causes of within-field field variation in yield variability. crop productivity? • Soil water holding capacity • It’s the water! • Redistribution of water over landscapes • Ability of roots to extract water • Compaction affects all of these 5 How can we measure compaction? Measuring Compaction • Directly: • Change in soil volume • Porosity • Bulk density Measuring Compaction Measuring Compaction • Bulk density • Soil cone penetrometer • Measures the resistance of the soil to vertical • Time consuming insertion of a cone • Difficult to compare • Cone Index (CI) in units of pressure – psi across soil types or MPa • Standardized by ASABE (American Society of Agricultural and Biological Engineers) to allow data comparison between devices/locations • Difficult to get consistent readings with handheld, human-powered units A. Soil Bulk Density 1.00 Y = 2.6 - 4.6X + 4.4X2 - 1.4X3 Compaction 2 R = 0.84***, n = 11 Measuring Compaction 0.75 vs. Yield When BD < 1.4 Mg m-3 then Y = -0.32X + 1.32 0.50 When BD > 1.4 Mg m-3 then Sandy loam Y = -1.58X + 3.08 0.25 Loam • Soil cone penetrometer Clay loam Relative Abovegroundyield • Human-powered units with electronic data 0.00 collection are more useful, but pushing them Using Penetrometer 1.01.21.41.61.82.0 -3 into the ground at a consistent speed can still Measurements Bulk density (Mg m ) be difficult 0 B. Penetrometer resistance F1-101 1.00 20 A 0.75 40 0.50 Depth, cm Bt1 Y = 0.98 - 0.20X R2 = 0.53*, n = 11 0.25 60 Bt2 Relative Abovegroung yield C1 Data from a greenhouse 0.00 80 study by Motavalli et al. 0.0 0.5 1.0 1.5 2.0 2.5 3.0 3.5 01234 Penetrometer resistance (MPa) CI, MPa using different Missouri soils 6 Compaction vs. Yield Compaction vs. Yield 0 0 3 F1-101 3 F1-101 20 A 20 A 2 2 40 40 Depth, cm Depth, cm Bt1 Bt1 1 Cropping System 1 Min-Till Corn-Soybean 60 60 Bt2 Bt2 No-Till Corn-Soybean C1 C1 No-Till Corn-Soybean-Wheat 80 80 0 0 01234 01234 CI, MPa CI, MPa Standardized Soybean Yield Standardized Soybean Yield Cropping System -1 -1 Min-Till Corn-Soybean No-Till Corn-Soybean No-Till Corn-Soybean-Wheat -2 -2 10 20 30 40 1.6 2 2.4 2.8 3.2 3.6 Depth to Maximum Cone Index, cm Maximum Cone Index, MPa Measuring Compaction Within-Field Variation Site 1 Site 2 Site 3 • Soil cone penetrometer • Automated units use a power source to push them into the soil and record data simultaneously • Trailer-mounted • Tractor-mounted • Improved data collection • But still a point measurement Within-Field Variation A New Compaction Sensing Approach • Desirable characteristics for a compaction sensor • Using a penetrometer, it’s difficult to collect enough • Rapid, efficient data collection at the intensity needed for data to understand how compaction varies across spatial within-field compaction mapping (i.e. on-the-go) fields • Describe compaction profile to identify the depth of restrictive layers • Tillage draft sensors can collect surface compaction- • Repeatable, consistent measurements related data on whole fields, but don’t indicate depth • One solution: variations • Tractor-mounted shank that collects soil strength data at multiple depths 7 Soil Strength Sensors Soil Strength Sensors • USDA-ARS, Auburn, AL (Raper et al.) • University of California (Upadhyaya et al.) • On-the-go Soil Strength Sensor (OSSS) • Compaction Profile Sensor (CPS) • One sensor tip, moves up and down • Five sensor tips to 40 cm depth • University of Nebraska (Adamchuk et al.) • USDA-ARS, Columbia, MO (Sudduth et al.) • Integrated Soil Physical Properties Mapping System • Soil Strength Profile Sensor (SSPS) (ISPPMS) • Five sensor tips to 50 cm depth • Blade-based sensor, measures total force and depth trend USDA-MO SSPS – 5 extended sensing tips USDA-MO SSPS Field Test Results • Sensor worked well in field tests, showing both short- Wiring range and longer-scale tunnel variations in soil compaction 4 Prismatic tip Depth=50 cm A 20 in. 3 Depth=40 cm 2 Depth=30 cm B * A: tip extension (2 in.) Depth=20 cm Load * B: tip spacing (4 in.) MPa PSSI, 1 cell Depth=10 cm 0 Main blade 160 170 180 190 200 210 Position, m * Width is 1 in. with cover on Compaction Mapping How can we manage compaction? 10 cm 20 cm 30 cm • Avoiding Compaction • Undoing Compaction 2.2 40 cm 50 cm 2 1.8 1.6 1.4 1.2 1 0.8 PSSI (MPa) 0.6 0.4 0.2 8 Avoiding Compaction Avoiding Compaction: Research Results • Reduced Axle Load • Assuming moist, arable soil: • Near surface • 4.4 tons/axle compacts to 12 in. • Compaction caused by specific pressure • 6.6 tons/axle compacts to 16 in. • Subsoil • 11 tons/axle compacts to 20 in. • Compaction caused by axle load • 16.5 tons/axle compacts to 24 in. and deeper • It’s common to see subsoil compaction persist for 6-7 years. Hakaansson, and Reeder, 1994 Approximate Axle Loads Avoiding Compaction Equipment Axle Load • Reduced Axle Load (ton/axle) • Minimize Tractive Element-Tire Contact 100 hp 2-wheel drive tractor 4 200 hp 2-wheel drive tractor 8 Stress (Spread the Load) 320 hp 4-wheel drive tractor 9 • Increased Tire Size 6-row combine (empty) 11 • Height 12-row combine (full) 26 • Width Single axle 27 yd3 grain cart (full) 22 • Tire Construction - Radial tires Double dual-axle 50 yd3 manure tanker (full) 35 (rear) 13 (front) Radial Tires & Proper Inflation Pressure Tractive Performance Data 18 psi 6 psi 9 Avoiding Compaction Benefits of Duals Duals Single • Reduced Axle Load • Spread the Load • Increased Tire Size • Tire Construction - Radial tires • Multiple tires Taylor et al., 1975 Avoiding Compaction Effects of Duals and Tracks on Soil Density • Reduced Axle Load 1.65 • Spread the Load 1.6 D-over • Increased