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NWISRL

NWISRL. Compaction and Soil Moisture. Far West Agribusiness Association 32 nd Annual Fertilizer & Chemical Conference Jackpot, NV January 10-12, 2005. Bob Sojka. Good News & Bad News. The Good News: We know quite a bit about soil moisture We know quite a bit about soil compaction

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  1. NWISRL Compaction and Soil Moisture Far West Agribusiness Association 32nd Annual Fertilizer & Chemical Conference Jackpot, NV January 10-12, 2005 Bob Sojka

  2. Good News & Bad News • The Good News: • We know quite a bit about soil moisture • We know quite a bit about soil compaction • We know quite a bit about their effects in many crops • The Bad News: • Alfalfa is not one of the crops we have a lot of specific information on for compaction NWISRL Kimberly, ID

  3. What We’ll Cover • Basic 3-phase Soil Physical Model • General plant responses to compaction • Effects of compaction on soil bulk density, strength, moisture, and aeration • Effects of soil moisture on compaction • Some data from Alfalfa • Some management tips NWISRL Kimberly, ID

  4. Three Phase Soil Model Sojka, 1999 NWISRL Kimberly, ID

  5. Three Phase Soil Model Sojka, 1999 NWISRL Kimberly, ID

  6. HARDNESS Soil Strength Mechanical Impedance Penetration Resistance Cone Index NWISRL Kimberly, ID

  7. Soil Gets Harder: When more compact When dryer Mirreh and Ketcheson, 1972

  8. Fundamental Soil Strength Relationships Derived from In-Situ Measurements Portneuf Silt Loam Subsoil 12-18” Plow Layer 6-12” NWISRL Kimberly, ID Sojka et al. 2001

  9. Corn Root Growth Through Subsoiled Portion of Hardpan Into Soft B Horizon Norfolk loamy sand Courtesy of Bob Campbell NWISRL Kimberly, ID

  10. When roots are forced to curve, branching Is Induced. Hard soil resists root penetration, bending the root, inducing branching, further reducing penetration Lateral Meristem Russell and Goss, 1974 NWISRL Kimberly, ID

  11. BD 1.2 BD 1.4 PEA Voorhees, 1975 BD 1.8 BD 1.6 NWISRL Kimberly, ID

  12. Amarillo Fine Sandy Loam COTTON Taylor and Gardner, 1963.

  13. Three Phase Soil Model SOIL AERATION: Compacting soil decreases the proportion and total amount of voids. The gases are pushed out. The water remains. Water fills a larger proportion of the remaining voids and the water films become thicker. O2 diffuses in through water only one ten-thousanth as easily as through soil air NWISRL Kimberly, ID

  14. COTTON Tackett & Pearson 1964

  15. Poorly Aerated Roots Close Stomata Sojka, 1988 NWISRL Kimberly, ID

  16. Low Root O2 Cuts Photosynthesis Oosterhuise et al., 1986 NWISRL Kimberly, ID

  17. Soil Oxygen in Alfalfa as Affected by Irrigation Meek et al., 1986 NWISRL Kimberly, ID

  18. Three Phase Soil Model WATER RETENTION: Compacting soil decreases the average size of voids. Less water is held at field capacity. Water is more subject to capillary action, so more water is available at greater suction (lower water potentials). If root growth isn’t restricted water can be available over a longer drying period… but roots have usually already been restricted NWISRL Kimberly, ID

  19. Compaction Squeezes Water Out of Big Pores But Holds Water Tighter in Small Pores This changes water holding properties and soil aeration properties Hillel, 1971

  20. Three Phase Soil Model WATER CONDUCTIVITY: Compacting soil decreases the average size of voids. Smaller pores, Less water flow at saturation. Water is more subject to capillary action, so more water flows in the dryer range (up to a point). NWISRL Kimberly, ID

  21. As Compaction Increases: Water flow through large pores decreases, but flow through small pores increases. Saturated Conductivity Decreases Unsaturated Conductivity Increases (to a point) High BD Low BD Carleton, 1971

  22. Compaction decreases the numbers of interconnected large pores, so infiltration rate decreases. Flocker et al. 1958 SSSAP 22:181-186

  23. SOFTNESS Plastic Limit: Wet enough for Permanent Deformation (Lower Plastic Limit) NWISRL Kimberly, ID

  24. SOFTNESS Liquid Limit: Wet enough to flow (Upper Plastic Limit) NWISRL Kimberly, ID

  25. Soils Compact More Easily as Water Content Increases

  26. Sandier Soil Compacts to Higher Bulk Density than Loamy or Clay Soils Hovanesian and Buchele, 1959

  27. Compaction Footprint Underground Is Wider Than the Tire Vanden Berg et al., 1957

  28. Depth of Compaction Increases With Load

  29. Dr. Al Trouse NWISRL Kimberly, ID

  30. Traffic/Tillage Pans Norfolk loamy sand NWISRL Kimberly, ID

  31. Soil Compaction in Alfalfa As Affected by Amount of Traffic Meek et al., 1988 6 inch 1 ft 2 ft NWISRL Kimberly, ID

  32. Determinate Southern Soybean Subsoiled at Planting Not Subsoiled Mr. Bob Campbell NWISRL Kimberly, ID

  33. Norfolk loamy sand CORN Sojka et al., 1991

  34. Pratt Fine Sandy Loam Fertilized SUGARBEET Root Weights kg Unfertilized

  35. Mapfumo et al., 1998

  36. Mapfumo et al., 1998

  37. Mapfumo et al., 1998

  38. Anti-Compaction Tips AVOID FIELD OPERATIONS ON WET SOIL Conserve Soil Organic Matter Control Wheel Traffic Patterns Minimize Operations and Traffic Keep Axle Loads to a Minimum Match-up Tractors, Implements, Tires, Trailers etc. Preserve Organic Matter and Soil Structure Break up Compacted Soil if Needed AVOID FIELD OPERATIONS ON WET SOIL NWISRL Kimberly, ID

  39. Structured vs Massive Soil • Soil without structure is more easily compacted • Structure provides voids for gas and water exchange and potential root channels • Soil Structure tends to be enhanced and stabilized by Soil Organic Matter and a mixture of particle sizes NWISRL Kimberly, ID

  40. Wet Soil: • Weakens structure (easy to compact) • Lowers O2 availability to plant roots • Favors microbial activity if warm • Can promote disease if prolonged • Can leach nutrients / agrichemicals • Can cause reducing conditions (Gaseous N-loss) NWISRL Kimberly, ID

  41. Sojka and Bjorneberg, Current Research Subsoiling Plus Polymers

  42. Mixing fines into sandy soils can worsen the soil strength of a compaction prone soil by achieving the “Minimum Void Ratio.” It takes 100s of tons of silt and clay per acre to convert a sandy soil to a loam (surface 6”).

  43. Only a few tons of manure per acre can change the tilth of the of a sandy soil, by promoting inter-aggregate structure, allowing the soil to perform more like a loam

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