Soils

The soil resource : 

The soil resource We get our food and natural fibers from ? In eastern US, takes 200 yr to form 2 cm topsoil What about the West? Soil erosion Erosion in undisturbed forests: ~ 0.0018 to 0.022 tons/ acre/ yr Overall rates in US: 7.6 tons/acre/yr What fraction of our topsoil have we lost in the US? For every inch of topsoil lost, corn & wheat yields drop by 6%

What is soil? : 

What is soil?

Where does soil come from? : 

Where does soil come from? Weathering of parent material Organic inputs from above Soil horizons O horizon organic, few cm thick (litter, fermentation, humus) A horizon topsoil, 10-30cm thick, plant roots E: (sometimes present) mineral sand & silt w/o clay, iron, or Al. B horizon intermediate weathering, larger particles, 30-60cm C horizon unconsolidated rock, partially weathered parent material, 90-120 cm

Organic Matter : 

Organic Matter Decomposed plants and animals; called humus Increases nutrient content of soil Nitrogen reservoir of soils Increases the amount of other nutrients (cation exchange capacity) Mineral soils: 1-10% OM; organic soils ~ 30% OM; swamps may be 90% Helps create soil structure Pore sizes influence rate of water movement Increases aeration Absorbs water:  water holding capacity Constantly undergoing change and must be replenished

Mineral Particles : 

Mineral Particles Sand 0.05-2.0 mm Silt 0.002-0.05 mm Clay < 0.002 mm Clay soils  water holding capacity, but not all available for plants. Also,  infiltration rates so  runoff What soils are best for agriculture?

Air & Water : 

Air & Water Air 25-50% by volume aerobic respiration Water 1 corn plant uses 100 liters/month 1cm3 soil has 150,000 root hairs plant available water is between field capacity and wilting point ( in clay soils,  in sandy soils)

Grassland Soil Systems : 

Grassland Soil Systems Climate, biota, parent material and time since last disturbance explains patterns of soil fertility within and among sites. North American mesic grassland soils are exceedingly rich (high in organic matter, nutrients) Shrubland soils are not very rich Grassland soils different from forest soils Biota have strong control on physical & chemical soil features Fire can also be an important factor for soil development -- especially soil fertility

Soil pH : 

Soil pH Why is pH important? Most soils pH 6-7, can support almost any plant Forest soils more acidic, even more if acid rain (pH 3-4) increases Fe, Mn, Al to toxic levels can neutralize by adding lime Highly alkaline soils poor, too lower availability of P can neutralize by adding sulfate

Salt-Affected Soils : 

Salt-Affected Soils Where is salt contamination more of a problem and why? What does salt do to plants? (Miller and Donahue 1990)

Colorado River Basin Salinity : 

Colorado River Basin Salinity How does salt get into the Colorado River? Estimated damages from salinity in the Colorado River is $500 to 750 million/yr!!! Why so high?? http://www.usbr.gov/dataweb/html/crwq.html

Colorado Salinity Control Program: Grand Valley Unit : 

Colorado Salinity Control Program: Grand Valley Unit 580,000 tons/yr of salt added to the Colorado River from the Grand Valley Much of this is due to irrigation return water and other seepage which picks up salts from the underlying Mancos shale Program reduces amount through underground pipelines, lined irrigation canals, drip irrigation, etc. Unit removes estimated 115,700 tons/yr salt at a cost of $93/ton http://www.usbr.gov/dataweb/html/grandvalley2.html

Managing salty soils : 

(Miller and Donahue 1990) Water control Leach salts before planting (seedlings are less salt tolerant than adult plants) irrigated lightly but frequently to keep salts from the surface Planting position Salts move with water so may accumulate in surface soil or furrow ridge Avoid planting on tops furrow ridges Managing salty soils

What makes some plants salt tolerant? : 

What makes some plants salt tolerant? Salt tolerant plants are called ______________ Some plants exclude uptake of salt by root cells Some plants accumulate high levels of sodium and chloride in tissues which can increase plant organic compounds in cells leading to a lower water potential Some plants excrete absorbed salts from the plant by means of “salt glands” that either burst, dripping out the high salt solution or finally drop off the plant

Selenium : 

Selenium What is selenium? Why is it harmful? Where does selenium in the Grand Valley come from? http://www.seleniumtaskforce.org (Grand Valley Selenium Task Force)