Flashcards in Final Deck (131)
Organic matter is responsible for ___ of CEC. It ______ soil aggregates, and increases __ ___ ____. Energy, Carbon and nutrients for _______
water holding capacity
Soil organic matter can be divided into 3 components:
Biomass- living organisms
Detritus- Identifiable dead tissue
Humus- nonliving,non tissue
a complex mixture of brown and black amorphous and colloidal organic substances that result from microbial decomposition and synthesis and has a chemical and physical properties of great significance to soils and plants.
What percent of carbon is lost to CO2 from organic residues breaking down?
Dark brown to black, high molecular wt.
Soulble in bases, not acids.MW up to 300000 g/mol
Yellow to red, lower molecular wt.
Soluble in base and acid. Mw 2000- 30,000 g/mol
Highly condensed completed with clays.
Non humic substances make up what percent of soil organic matter? they are (more or less) complex chemically? (More or less) resistant to decomposition? The chemical and physical structure is _______?
Humic substances make up what percent of soil organic matter? they are _____. they are _____ in color and have a _____ molecular weight? _____ resistant to microbial attack?
Organic matter soil physical properties-(4)
Dark brown to black surface horizons
Improved soil aggregation
increased water infiltration
Increased water holding capacity
CEC,______ accounts for 50-90% of CEC in surface soils. and provides much of the ______________ in soils.
pH buffering capacity
provides most of the food for heterotrophic soil organism, especiall for the detritus fraction.
Provides nutrients for plants.
Diversity of organic matter increases diversity of soil organisms.
Soil organic matter increases or decreases depending on balance between?
Where do the gains come from?
Where do the losses come from?
gains and losses of carbon.
Gains- from plant residues grown in place or applied organic matter
Losses- from respiration, plant removal, and erosion.
How does temperature influence amount of organic matter?
at low temps, plant growth is greater than decomposition, organic matter accumulates.
How does moisture influence amount of organic matter?
more moisture means more organic matter
How does vegetation influence amount of organic matter?
more organic matter under grassland than forest
How does Soil texture influence amount of organic matter?
more organic matter in finer textured soils.
How does drainage influence amount of organic matter?
poorly drained soils accumulate more organic matter.
How does Tillage influence amount of organic matter?
decreases organic matter. aerates soil and breaks up residue
Guidelines for managing SOM(5)
add continuous supply of plant residues, animal manuers.
Ideal amount of SOM depends on soil, plants, and climate.
Encourage perennial vegetation
Soil microorganisms need N in addition to C.
1g of N for every 24g of C
If C/N ratio exceeds 25:1 what happens
Microbes will need to get N from soil
Plants could suffer from N deficiency
Decay of organic matter could be delayed.
creating humus-like organic materials by aerobic decomposition outside the soil.
Organic residues have been allowed to undergo biological decomposition.
Composting in large aerated piles; heat builds up within the compost piles.
3 stages of thermophillic compostion-
1. Mesophillic stage-
2. Thermophillic stage.
3. curing or 2nd mesophillic stage.
sugars and readily available food is metabolized; temps to voer 40C
decomposition of cellulose and other resistant materials; 50-70C
Curing or Second mesophillic stage-
temp falls to near ambient levels