Soils

Posted: October 13, 2011 in Soil
Tags: , , , , , ,

Complicated issues regarding irrigation scheduling:

-Water quality ( salinity) Influences the availability of soil water to plants.

-Irrigation systems have inherent qualities which restrict the frequency, rate, or duration.

–1/2 inch irrigation with furrows=non uniformity

–1/2 inch irrigation with center pivot= ineffective.

NON-ET based consideration:

Frost control

Softening soil crust

Herbicide incorporation.

External Factors:

Labor schedules

avoiding equipment interference

Availability of water ( Irrigation district or pump Time-of-use schedule

Parks–avoid weekend irrigation.

Soil triangle:

Sand, clay, silt.

Soil has 2-5% organic material.

Soil textures:

AG: Deep plow or importing huge amounts of soil.

Land Scape: Importing amending soils.

Horizons:

-Layers of soil with different characteristics.

-texture ( upper layers sometimes sandier than deeper layers)

-Structure

-Color

-Organic matter. ( generally top foot of soil.)

Nutrients:

Find in soil solution.

Cation exchange capacity-CEC: measure of the amount of negative charges in a certain weight of a soil (meq/100g)

Sand and silt have little or no CEC.

Clay: super absorbent. Negatively charged.

Reasons for poor structure————————————

Irrigation management

–affects top of the soil surface

–Influences infiltration rates

–Irrigation water wit h a high percent of sodium

–Irrigation water with high ratio of Mg/Ca

–Irrigation water which is very pure

–Large droplets caused by sprinklers with low pressures

–Furrow irrigation: structure changes with each irrigation

–Beginning of season: freshly plowed and large clods.

Soil moisture Definitions:

-Soil moisture reservoir

–soil acts as a reservoir for moisture

–fills up and empties.

Soil moisture tension ( matrix potential)

–Matrix potential is greater with clays ( smaller pores) than with sands

–as soil dries out, water is held in smaller pores.

 

LOAM SOIL: Best soil. 3o% silt,30% clay, 30% sand

25% air

25% water

50% Soil solids

Water is held in the ‘pore space’

 

The matrix holds water by surface tension just like capillary tubes.

 

Osmotic potential: Gets the water into the roots.

 

FC-Field Capacity-

The upper limit of soil water in the soil.

Soil moisture Characteristic curve-

Determined by lab.

Shows h20 content.

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