Alex Stone, Oregon State University A.Stone: Stone: Soil Biology A. Biology Workshop Workshop2/5/02 2/5/02
King et al, 1934
“..the manure increases the number and activities of competitive organisms which inhibit the growth and development of the root rot fungus.” A. Stone: Soil Biology Workshop 2/5/02
Stone: SoilBiology BiologyWorkshop Workshop 2/5/02 2/5/02 A. A. Stone: Soil
Effects of Organic Matter and Cover Crops on Soil Properties BIOLOGICAL PROPERTIES: disease suppression • Shift the soil community to more desirable organisms with specific biological control activities reduce pest incidence
A. Stone: Soil Biology Workshop 2/5/02
How Can Organic Matter Management Reduce Disease Severity? Suppression of the pathogen: • destruction of the pathogen • competition for space or nutrients Effects on the plant: • induced resistance to root and foliar diseases
Restoration of Root Rot Suppression in Avocado Orchards • Avocado root rot (P. cinnamomi) in avocado orchards • “Ashburner System” - continuous legumemaize cover crops, straw mulch, 4T/A poultry manure, pH maintained above 6 • Suppression is biological (destroyed by heating), and is generated by pathogen suppression. • Suppression originates in mulch. Malajczuk, 1983 A. Stone: Soil Biology Workshop 2/5/02
Trichoderma
Phytophthora hyphae Malajczuk, 1983 A. A. Stone: Soil Stone: SoilBiology BiologyWorkshop Workshop 2/5/02 2/5/02
Competition for nutrients • most fungal propagules require “signal” nutrients from the host to germinate and cause infection • in the absence of these signals, the pathogen propagules won’t cause disease • fungal pathogens also require nutrients to grow and infect • a very large and active microbial community scavenges those nutrients, reducing disease severity. Chen et al, 1987
A. Stone: Soil Biology Workshop 2/5/02
conducive soil
suppressive soil
Malajczuk, 1979 A. Stone: Soil Biology Workshop 2/5/02
Malajczuk, 1983 A. A. Stone: Soil Stone: SoilBiology BiologyWorkshop Workshop 2/5/02 2/5/02
from the USDA Soil Biology Primer A. Stone: Soil Biology Workshop 2/5/02
SOM is Compositionally and Functionally Heterogeneous Pool Biologically Active
Size/Age (yrs) Small/1-5
Protected
intermediate/ 5-30
Stable
Large/ 50-10,000
Functions The Meat: nutrient mineralization, macro-aggregation, disease suppression The Bones: soil structure, porosity, water relations Micro-aggregation, CEC, fate of ionic and non-ionic compounds, color A. Stone: Soil Biology Workshop 2/5/02
What Can We Learn from the Nursery Industry? Longevity of Root Rot Suppression Percent Biocontrol Organisms