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:

- Seasonal

- ‘Perched’

- 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:

1. Sufficient.

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

cumulative ET

B. Improving WUE of crops: many ideas here:

1. High yielding varieties

2. Mulches:

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

10. terraces

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

17. others?

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.