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:
Softening soil crust
avoiding equipment interference
Availability of water ( Irrigation district or pump Time-of-use schedule
Parks–avoid weekend irrigation.
Sand, clay, silt.
Soil has 2-5% organic material.
AG: Deep plow or importing huge amounts of soil.
Land Scape: Importing amending soils.
-Layers of soil with different characteristics.
-texture ( upper layers sometimes sandier than deeper layers)
-Organic matter. ( generally top foot of soil.)
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————————————
–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
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.
The upper limit of soil water in the soil.
Soil moisture Characteristic curve-
Determined by lab.
Shows h20 content.