AGEN 2363, Chpt. 13 notes. Water Conservation.
I. Importance of water to agriculture and non-agriculture use:
1. 80% + water used in U.S. devoted to agriculture
2. Irrigated crops necessary for profits in most arable regions.
3. Water and quality of water of national security.
II. The Water Cycle: know it!
A. Surface water sources:
- streams, ponds, lakes, reservoirs. What is the difference between a lake and a reservoir?
B. Ground water sources:
- confined aquifier, EX Sparta
- unconfined aquifer, EX alluvial
- know what the ‘static’ water table is
Some aquifers cover extremely large, multi-state areas.
III. Water and plants.
A. Three types of plant water status:
2. ‘Hidden’ –
3. Visual –
B. Four soil-water status regimes:
1. field capacity =
2. permanent wilting point = -15 bar
3. ‘available’ water = -0.2 - -15 bar
4. ‘readily available’ water = -0.2 - -1 bar
C. Soil water holding capacities by texture:
loams, silt loams, fine sandy loams: 2.2-2.4 in/ft
clays 2.0-2.2 in/ft
sandy loams 1.6-2.0 in/ft
sands 1.2-1.6 in/ft
D. Evapotranspiration (ET) = evaporation + transpiration water use by crops
1. ‘Potential’ ET (ETp) =
2. Actual ET (ETa ) =
3. Factors affecting ETa :
E. Three mechanisms plants use to avoid drought stress:
1. escape –
2. evade –
3. endure –
F. Total water balance of a crop:
1. inputs: rain, irrigation, snow melt, dew, upward wicking from subsoil
2. outputs: runoff, deep percolation, evaporation from soil surface, plant transpiration
IV. Water use efficiency of crops.
A. Water Use Efficiency (WUE) = harvestable yield
B. Improving WUE of crops: many ideas here:
1. High yielding varieties
3. irrigation systems:
micro-irrigation > sprinkler > 0 grade flood > furrow or flood
4. crop rotations
5. multiple inlets in flood or border
6. ‘surge’ irrigation techniques in furrow
7. conservation tillage systems
8. fallow farming in semi-arid dryland systems
9. sub-soiling fields with traffic pans
11. contour cultivation
12. ‘water harvesting’ methods in orchards, horticulture plots in semi-arid regions
13. weed control
14. wind breaks
15. soil test, optimum fertilization programs
16. nematode and other disease and insect pest control
V. Irrigation scheduling.
A. Soil-water sensors: - tensiometers
- neutron radiation
- TDR sensors
- ‘watermark’ type sensors
B. Arkansas ‘Check Book’ method. Examples will be performed in a laboratory exercise.