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Cover crops & soil compaction
This document discusses soil compaction, its causes and impacts, and strategies for mitigating compaction through reduced tillage and the use of cover crops. It notes that soil compaction physically impedes root growth, limits water and nutrient uptake, reduces infiltration and aeration, and increases risks of stress, disease and poor fertilizer efficiency for crops. Cover crops like rye and forage radishes are presented as tools to alleviate compaction through their root systems. Research shows that forage radishes in particular have a large, deep taproot capable of penetrating compacted subsoil layers and improving soil structure. The document emphasizes the importance of cover crop root systems and provides evidence from studies using imaging and root counting methods.
Cover crops & soil compaction
- 1. Soil Compaction &Cover Crops Ray Weil rweil@umd.edu Professor of Soil Science Dept. of Environmental Science and Technology.
- 2. What is soil compaction? Polarized light microscope
- 3. Compaction from traffic& tillage
- 4. AgriCanada Without restricted traffic, most field Chiseling surfaces receive traffic each year
- 5. Structural damage sensitivity index Damage to soil structure is worst when soil is wet and organic matter is low! Watts, C.W., and A.R. Dexter. 1997. Soil and Tillage Research 42:253-275.
- 6. Soil compaction: whythe concern? Physically impedes root growth Limits water/nutrient uptake from subsoil Reduces infiltration, drainage drought & ponding Reduces Oxygen diffusion into soil – yes, roots need to breathe!! Poor aeration favors fungal root diseases Reduces fertilizer use efficiency Increases risk of soil-applied herbicide injury
- 7. Crop stress dueto impaired root function
- 8.
- 9. Less tillage ,less long-term compaction
- 10.
- 11. ><-2 MPa 1 12MPa MPa http://www.bettersoils.com.au/module6/6_3.htm
- 12. CM0 CM5 CM10 Chestertow n 02/02 Plow pans and traffic pans Soil Depth CM15 CM20 CM25 Plow Pan persist, even under CM30 no-till. CM35 CM40 CM45 0 00 000 000 000 000 000 000 Hayden Farm, 03/04/03 10 2 3 4 5 6 7 Penetration Resistance, kPa CM_0 CM_5 CM_10 Soil Depth CM_15 CM_20 CM_25 Plow Pan CM_30 CM_35 CM_40 CM_45 0 1000 2000 3000 4000 5000 6000 7000 Penetration Resistance, kPa
- 14. Map of Compactionlevels varying within a field. 1000 kPa = 145 PSI Kilo Pascals (kPa) atkPa at (14 inches) deep Hayden, 35 cm 35 cm 0 25 180 200 00 20 East_West, Ft 0 200 1500 00 15 0 200 50 20 2000 00 1 00 120 0 00 0 200 50 150 15 200 1 20100 0 00 0 2000 00 0 250 20 0 0 2500 30 60 35 4500 0 0 200 00 500 1500 00 00 400 200 6000 200 55 00 0 0 0 15 0 -20 70 160 250 340 430 520 North ---South, Ft
- 15. Soil water content influence on soil strength Penetration resistance is Clay subsoil meaningful only in context of a certain moisture condition. So don’t let an equipment salesperson test your soil strength in the summer! Data of Gilker and Weil
- 16. More than JustCover: Cover Crops as Multiple Purpose Soil Quality Mgt. Tools Soil Food Cover Cooler Aggregation web Weed crops soil suppression Labile C Soil Crop Nematodes Soil water growth Bio- organic Bio- drilling matter Nitrogen drilling Nitrogen fertility leaching
- 17. Rye effect ontopsoil bulk density (g/cm3) in Spring 1.65 Rye killed May 1 1.6 Rye killed May 15 1.55 0-4” 1.5 a a a depth 1.45 1.4 b 1.35 w/o Rye with Rye 1.65 1.6 ab a 4-8” ab 1.55 depth b 1.5 1.45 1.4 1.35 w/o Rye with Rye With Rye w/o Rye Both samples under manure spreader tracks on dairy farm operation Data and photo from Sjoerd Duiker - PSU
- 18. Rye roots ina compacted soil Not very good at soil penetration
- 19. Forage radish Key differences are in the roots!
- 20. Forage radish: •kills itself •suppresses winter weeds Rape Rye Forage radish
- 21. “Weil’s Law” of root/shoot ratio effects 1. If conditions above ground are limiting, the roots will suffer most. e.g. late planting or crowding (above ground limit) decreases root/shoot ratio. 2. If conditions below ground are limiting, the shoots will suffer most. e.g. N deficiency or drought (soil limit) increases root/shoot ratio +N -N
- 22. Effect of seedingdate on forage radish root & shoot growth in fall Dry matter (shoot or fleshy root), kg/ha 5000 0.8 Means of four sites (measured Dec. 1) 0.7 4000 Shoot 0.6 Root/shoot ratio 3000 0.5 2000 Root/shoot ratio 0.4 0.3 Root 1000 0.2 0 0.1 1 2 3 4 5 Seeding date (weeks after August 20)
- 23. Bulk densities (Mg/m3) uncompacted compacted Larger diameter roots have greater ability to penetrate compacted soil 0 1.14 1.16 10 1.25 1.57 20 1.32 1.43 Data from: Materechera, S, M. Alston, J Kirby, and A.Dexter. 1992. Plant and Soil 144:297-303.
- 24. Which answer to compaction? “Radish – Ripper” Steve Groff Ripper Radish
- 25. But – how tolearn what the roots are doing down in the subsoil?
- 26. One approach: WaterTension at 50 cm (20 inch) depth Changes in Soil monitor summer as affected by preceding fall cover crop. during crop use of water from the subsoil June July August Wet Dry
- 27. Investigating roots withfiber optic camera: minirhizotron Subsoil 16 in (40 cm) deep Wye, Md – silty clay loam Subsoil 17 in (42 cm) deep Groff farm – clay loam
- 28. First published proofof “bio-drilling” to alleviate subsoil compaction Rapeseed root Williams and Weil (2004)
- 29. Compaction Experiment (Don’t try this on your farm!) 3 compaction levels: • No: no pass • Medium: one pass • Heavy: two passes For each pass Wt: 1.19*104 kg contact area: 1600 cm2 force: 7.44*104 N
- 30. Rye and RadishCover Crops in Forage Radish roots under Dec. after compaction no or heavy compaction Note: the whole experimental site was disked to 8 cm (3 inches) to provide a suitable seedbed before planting cover crops.
- 31. Learning about rootsthe hard way – digging them up and counting them! Core-break method to determine at root numbers with depth. Counting root numbers at Taking soil core to a depth of 60 cm the breakage faces Three cores per plot
- 32. Root penetration capabilityof 3 cover crop growing under heavy compaction * * * * * * FR had 2 to 4 times as Soil depth, cm many subsoil roots as * rye or rape * * * * * * Roots per 32 cm2 Chen and Weil, 2010 Differences of root numbers (per 32 cm2) at each depth are indicated by *; student t-test, a=0.05
- 33. Roots of corn following rye, radish or no winter cover crop Plow depth 45 cm2 Late July Chen and Weil, unpublished
- 34. Think about… Managing plantsto soils soils improve plants Stick around for the Q and A Panel!
- 35. We want towork with you! If you are interested in using cover crops for…. • Early spring vegetable crops • Reduced or no-till planting • Please fill out the survey and • pick up a sample of Tillage™ Radish seed