Organic Matter The key to healthy soils Fred

Organic Matter The key to healthy soils Fred

Organic Matter The key to healthy soils Fred Magdoff Dept. of Plant & Soil Science University of Vermont Are these compact soil problems or

low nutrient symptoms levels ? droughty many pest problems erosion and runoff Symptoms compact soil low nutrient

levels droughty many pest problems erosion and runoff Problem Degraded Degraded and and unhealthy

unhealthy soil soil Why are soils which in our fathers hands were productive now relatively impoverished? The depletion of the soil humus supply is apt to be

a fundamental cause of lowered crop yields. J.H. Hills, C.H. Jones, and C. Cutler, 1908 Soil Soil organic organic matter matter and and its

its management management are are at at the the heart heart of of soil soil health health

Characteristic s of Healthy Sufficient (but Soils not excess) nutrients Good tilth Sufficient depth

Good water storage and drainage Free of chemicals that might Characteristic s of Healthy Low populations of plant disease and parasitic Soils

organisms High populations of organisms that help plant growth Low weed pressure Resistance to being degraded Sustainable Agriculture Healthy Plants

Healthy Soils Soil Organic Matter There are three general types of organic matter in soils Living Dead Very Dead bacteria

plant roots nematodes fungi Living earthworms mites moles

springtails fungi nematode& small Root

Root hair Soil ecology in balance Tighter system More fluid / greater biological diversity Low disturbance Crop rotation Direct seeding Build organic matter

Permanent planting Infiltration Cover cropping Drainage Irrigation management Soil fertility / slow nutrient

release Manure / biosolids Neutral pH Moisture conservation Residue cover MANAGEMENT PRACTICES INFLUENCE ECOLOGY High disturbance Tillage Burning Steam sterilization

Fumigants Monoculture Herbicides Overgrazing Fungicides Insecticides Changing ecology of system

Imbalance in species Some groups increasing in number; some groups eliminated Dead Dead Recently Recently dead dead soil soil organisms organisms and and crop

crop residues residues provide provide the the food food (energy (energy and and nutrients) nutrients) for for soil soil

organisms organisms to to live live and and function. function. Also Also called called active active or or particulate

particulate organic organic matter. matter. Very Very Dead Dead Well Well decomposed decomposed organic organic

materials, materials, also also called called humus. humus. Humus Humus contains contains very very high high amounts amounts of

of negative negative charge. charge. All All three three types types of of soil soil organic

organic matter matter play play important important roles roles in in helping helping produce produce high high yields

yields of of healthy healthy crops. crops. Soil organic matter Organic matter is 1-6% of total soil mass living 10-20%

humus active (dead) (very dead) 10-20% 60-80% Organic Matter Influences a Vast Number of Important Soil Properties For Example: Nutrient availability Aggregation (and infiltration and drainage) Water storage

Diversity and activity of soil organisms Soil color Presence of growth stimulating compounds Important global cycles carbon, nitrogen, and water are strongly influenced by soil organic matter Nutrient Availability

As organic matter is decomposed nutrients are transformed into forms that are available to plants. From 50% to close to 100% of the CEC is due to soil organic matter

Organic matter level 20 16 7% CEC due to 12 organic

matter (me/ 8 100g soil) 5% 3% 4 0 4.5 6.0

1% 5.0 6.5 pH 5.5 7.0 Ca++ Ca++ - Ca++ --- - +- K Mg++-++

- Ca a) cations held on humus Ca++ Mg++ - - -- K+ b) cations held on clay particle

- Zn++ c) cations held by organic chelate Cation Exchange Capacity

Figure 4.3 Cationnutrients held on negatively charged organic matter and clay. and chelation QuickTime and a Photo - JPEG decompressor are needed to see this picture. Corn grown in

nutrient solution with (right) and without (left) humic acids. Photo by R. Bartlett. Soil Tilth QuickTime and a decompressor are needed to see this picture.

infiltration a) aggregated soil runoff b) soil crusts after aggregates break down Root heavily infected with mycorrhizal fungi

(note round spores at the end of some hyphae). Photo by Sara Wright. Sticky substance, glomalin, surrounding root heavily infected with mycorrhizal fungi. Photo by Sara Wright. Sticky substance, glomalin, surrounding soil

aggregates. Photo by Sara Wright. carbon dioxide (CO2) (0.04% in the atmosphere) respiration in stems and leaves photosynthesis crop and

animal residues carbon in soil organic matter root respiration and soil organic matter decomposition crop harvest

erosion The role of soil organic matter in the carbon cycle. Losses of carbon from the field are indicated by yellow color around the words describing the Karen Hills, 2007 Add organic

matter Increased biological activity (& diversity) Reduced soil-borne diseases, parasitic nematodes Aggregati on increased

Pore structure improved Decomposition Humus and Nutrients released other Harmful growth

substances promoting Improved tilth detoxified substances and water storage HEALTHY PLANTS 160 Yield (Bu/A)

140 y = 82.3x - 54.9 r2 = .78 120 100 80 60 40 20

.8 1 1.2 1.4 1.6 1.8 2.0 2.2 2.4 Soil organic matter (%) Relationship of corn yield and soil organic matter at the end of a long term cropping experiment

Two Two conditions conditions are are necessary necessary to to maintain maintain an an adequate adequate amount amount of

of organic organic matter matter in in the the soil. soil. These These are, are, first, first, an an adequate

adequate supply, supply, and and second, second, avoidance avoidance of of aa too-rapid too-rapid loss... loss... Lyon Lyon and and Fippin.

Fippin. 1909. 1909. QuickTime and a decompressor are needed to see this picture.

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