Cover Crops Can Help Maximize Available Soil Moisture Rachel Stout Evans Soil Scientist USDA-NRCS Metcalfe Soil Survey Office
When the earth will drink up the rain as fast as it falls. -H.D. Thoreau, The Journal
What is Available Soil Water and Where is it stored?
Available Water Water
Ideal Soil Composition Pore Space Solids 25% Water 25% Air 45% Mineral 5% Organic Matter MRBI: Managing Cover Crops A Farmer s Perspective by David Brandt
Organic Matter MICROPORES H2O MACROPORES H2O Soil Minerals
What affects the Available Water Capacity of a Soil? And can we change those things? Available Water Water
1) Amount and Size of Pore Space 2) Amount of Soil Organic Matter Organic Matter MICROPORES H2O MACROPORES H2O Soil Minerals
Pore Space: Water and Air Movement and Storage Macropore Space Macro and Micropore Space Micropore Space
Loss of Pore Space = Compaction
So, what do Cover Crops do?? Metcalfe, MS 4 Dec 2014
Above Ground Cover Bare Soil Decrease Rain Drop Impact Velocity Slow Surface Runoff Increase Rain Water Infiltration into Soil Protect from Erosion
Below Ground MRBI: Managing Cover Crops A Farmer s Perspective by David Brandt Metcalfe, MS 4 Dec 2014
Living Roots in Your Soil Fall, Winter, and Spring Physical, Biological, Chemical Activity Pore Space + Organic Matter = Available Water Capacity Long Term Water Storage
New Roots Physical Roots create macropores - water and air channels Old Roots Roots grow and regrow along same paths year after year, creating larger channels
Eudora, AR Rooting Depth and Root Size depends on Plant Species Soil Type (texture) Soil Density (compaction)
Plant Species: Tillage Radish (tuber/tap) Rape (tuber/tap) Winter Pea (fibrous) Clover (fibrous) Cereal Rye (fibrous) Plant Species: Tillage Radish (tuber/taproot) Triticale (fibrous grass root)
Metcalfe, MS Tap Roots and Fibrous Roots in Sharkey Clay and Commerce Silty Clay Loam
Macropores
Soil Density Compacted layer plow pan at 4 inches, Bruin very fine sandy loam First year of planting tillage radish
Fibrous grass (Triticale) roots penetrating compacted layer (plow pan) in Bruin very fine sandy loam Eudora, AR First year of planting cover crops
Open field Oilseed Radish field Soil compaction decreased by >40% Long Term Cover Cropping Penetration Resistance
Fibrous Roots at 30 inches in Dundee silty clay loam, Yazoo County
Root Growth and Pore Space with Compacted Layer Root Growth and Pore Space without Compacted Layer Plow pan Network of biopores MRBI: Managing Cover Crops A Farmer s Perspective by David Brandt
Biological/Chemical More and deeper roots to find and use more water Living roots + little disturbance = Mycorrhizal Fungi Hyphae AND Earthworms (Soil Organisms)
Mycorrhizal Fungal Hyphae and Plant Roots
MYCORRHIZAL FUNGI A symbiotic association between fungi and plant roots Fungi serve as a bridge to bring nutrients (N, P, and micronutrients) to plant roots Under dry conditions, fungi can bring moisture to the roots they colonize
Mycorrhizal Fungus S Source: Better Soils for Better Crops
Sticky substance, glomalin, surrounding root heavily infected with mycorrhizal fungi. Fungi help roots explore up to 20% of the soil volume. A root by itself can only explore 1% of the soil volume. Photo by Sara Wright.
Soil Critters, Bacteria, and Fungi Shred organic material Stimulate further microbial activity Convert dead organic material into useful organic acids and mineralized nutrients Decompose residues and break down nutrients for plant availability Nutrient Cycling: Eat other soil critters and release nutrients for plants Convert NH4+ to NO2- to NO3- (plant available N)
EARTHWORMS Of all the members of the soil food web, earthworms need the least introduction Their presence is usually an indicator of a healthy system
Decomposers Earthworm pulled plant residue into burrow EARTHWORMS IN AGRICULTURE Increase infiltration. Earthworms enhance porosity as they move through the soil. Some species make permanent burrows deep into the soil. Bury and shred plant residue Earthworms eat residue, digest and excrete rich organic matter
Cover crop root mass Creates and enlarges pore spaces through the soil, allowing more air and water to move through and be stored Excretes carbon and sugars for soil critter food Hosts beneficial fungi to gather more water and nutrients for plants Hosts earthworms, which create more pore space and organic matter Contribute organic matter as they decompose
Water Uptake 0 6 12 18 24
Increased Water Storage Capacity Equals less Flooding 50% Void Space Equals 3-4.5 inches of additional water storage capacity. Illustrated by Cheryl Bolinger-McKirnan & Jim Hoorman
Greenville
Helping People Help the Land
0 Root Growth and Pore Space with Compacted Layer 0 Root Growth and Pore Space without Compacted Layer 6 6 8 Plow pan 8 Network of 12 12 biopores 15 15 20 20 MRBI: Managing Cover Crops A Farmer s Perspective by David Brandt
Mississippi Alluvial Aquifer is how irrigate our farmland Here in the Mississippi Delta
Cover Crops: Use Multiple Species for different root growth habits and functions
Cover Crops Can Help Maximize Available Soil Moisture Thank you