Managing Soil Physical Properties Dr. Steven Green 29 October 2014 Southern Agricultural Cover Crops Conference Jonesboro, AR @AStateCoAt
Objectives Identify some important soil physical properties Understand the function of these soil physical properties Understand the role of cover crops in soil physical function Understand the connection between soil biology and soil physical properties
Laws of Ecology: Barry Commoner Everything is connected to everything else Everything must go somewhere Nature knows best There is no such thing as a free lunch
Physical Soil Properties Soil Structure Aggregate Stability Bulk density/compaction Water Infiltration Surface Crusting Available Water Holding Capacity
Physical Soil Properties Soil Structure Aggregate Stability Bulk density/compaction Water Infiltration Surface Crusting Available Water Holding Capacity
Soil Structure Arrangement of soil particles into larger units Peds Aggregates Clods Functional influence on Infiltration Soil erosion Runoff Root penetration Organism habitat Abertay University
Structure
Aggregate Stability Ability of aggregates or peds to resist disruption Functional influence on Erosion Infiltration Root growth www.abc.net.au
Bulk Density/Compaction Mass per unit volume Reduction of pore space Functional influence on Water and gas exchange Root penetration/root growth Biological habitat Building Soils for Better Crops, 2009
Role of Cover Crops Photos by Steve Green and Jami Nash, Jonesboro AR
Cover Crops Rhizosphere Root penetration Organic matter Organic glues
Rhizosphere This is where the action is Very high microbial activity Root exudates and microbial exudates The immediate zone around the root Usually within 2 mm from root surface Microbial numbers 2 to 10x that of bulk soil Cover crops provide rhizosphere during non cash crop time of the year
Root Penetration Don t underestimate the strength of the root Some can penetrate compacted layers Rye and wheat Sorghum sudan Radish Sweet clover and red clover
Organic Glues Humic acids Glomalin Polysaccharides Function Binding particles together Glomalin not easily broken down naturally Glomalin produced by mycorrhizal fungi associated with most plants (except in Brassica plant species)
Glomalin Glomalin (noun). A strong glue, glomalin, is produced by a beneficial fungus that grows on plant roots. The glue comes off of the fungus and is deposited on soil particles. This process leads to build up and stabilization of aggregates. --Glomalin, A manageable soil glue (Sara Wright)
Glomalin and Soil Management Green, Wright, et al. (2007) Soil Tillage Research 94:546 549.
Glomalin and Soil Management Wright and Upadhyaya (1998) Plant and Soil 198:97 107.
Cover Crops to Enhance Glomalin and therefore, aggregate stability Key is to enhance (and not reduce) mycorrhizal fungi in the soil (Don t ruin the habitat) Keep a root in the soil at all times (these fungi are root associated) no root = no fungi = reduced glomalin = reduced aggregate stability = poor structure = less infiltration = more runoff = less water for plant = less yield or more inputs = lower profits = sad farmer Legumes greater association with mycorrhizal fungi Clovers Winter pea Vetch
Organic Matter Soil organic matter Heart beat of the soil Provides greater porosity Reduces overall bulk density Increases water holding capacity Allow soil to give Covers that increase organic matter in a big way Cereal rye Winter wheat Barley Sorghum sudangrass Subterranean clover Berseem clover Cereal rye, 2014; 4.6 ton/acre dry biomass (May 1). Photo by Green in Jonesboro
Cover Crops Increase organic matter Enhance aggregate stability Break up compaction Results in: Better root penetration and establishment Increased infiltration Greater water holding capacity
Structure
Don t forget about the structure Lack of structure = lack of function