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
- 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
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