4 BRAE 236 Soil Plant Water

4 BRAE 236 Soil Plant Water - Basic Soil, Plant and Water...

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1 Basic Soil, Plant and Water Relationships Purpose of Soil • Moisture reservoir • Nutrient reservoir • Mechanical support
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2 ET Definitions • Transpiration Transpiration : liquid movement of water from the soil into the roots up the plant stems and finally soil, into the roots, up the plant stems, and finally out of the plant leaves into the air as vapor • Evaporation Evaporation : conversion of liquid to vapor from the soil or plant surface from the soil or plant surface-- --this water does not this water does not move through the plan move through the plant • Evapotranspiration (ET) Evapotranspiration (ET) : combination of evaporation and transpiration Irrigation Scheduling Need to answer 2 basic questions: • When to irrigate? • How much to apply?
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3 Complicated issues regarding irrigation scheduling Soils have different moisture holding characteristics Soils have different moisture holding characteristics: soil depth available water relationships between soil moisture depletion and matrix potential due to texture Complicated issues regarding irrigation scheduling Plants differ in their abilities to withdraw Plants differ in their abilities to withdraw water from soils cotton needs to be stressed vines need to be stressed Plants differ in their water use rates citrus vs. alfalfa (by a factor of 2)
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4 Complicated issues regarding irrigation scheduling Water quality (salinity) influences the availability of soil water to plants Irrigation systems have inherent qualities which restrict frequency, rate, or duration 1/2 inch irrigation with furrows = non-uniformity 1/2 inch irrigation with center pivot = inefficient Non-ET based Considerations • Frost control • Softening soil crust • Herbicide incorporation • Irrigating cover crop or wind break
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5 External factors • Labor schedules • Avoiding equipment interference • Availability of water – irrigation district limitations – pump Time-Of-Use electric schedule • Parks--avoid weekend irrigation Soil Texture: ratios of various sizes of soil particles • Clay < .002 mm dia • Silt < .05 mm dia • Sand < 2.0 mm dia
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6 Changing Soil Texture • Agriculture: deep plowing or importing huge amounts of soil • Landscape: importing or amending soils
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7 Horizons • Layers of soil with different characteristics – texture (upper layers are sometimes sandier than deeper layers) – structure – color organic matter (generally in top foot of soil – organic matter (generally in top foot of soil) Ground Surface Sandy Loam - 1 ft Horizons Clay Loam - 1.5 ft Clay Loam - 1.5 ft Sandy Loam - 1 ft Sandy Clay Loam
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8 Nutrients • Found 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 Soil Structure • The way that various soil particles are held together and oriented with respect to each other • Good structure: many large pore spaces allowing movement of water and air • Can be influenced by irrigation management
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This note was uploaded on 11/12/2011 for the course BRAE 236 taught by Professor Styles during the Spring '08 term at Cal Poly.

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4 BRAE 236 Soil Plant Water - Basic Soil, Plant and Water...

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