Irrigation scheduling is using water management strategies to keep optimum water balance in the soil profile; or optimum available soil moisture (ASM) for that crop through the growing
season. Each crop's optimum water balance is different. For potatoes, the optimum ASM for about 75% of its' growing season would be between 70-90% ASM. The goal of irrigation
scheduling is to keep the potato crop in that optimum range of 70-90% for 75% of its' growing season. You are applying the proper water amounts that match ASM and evapotranspiration,
or ET's, for that crop at that time period of growth.
In simple terms, irrigation scheduling is applying the right amounts of water at the right time frame for that crop's stage of growth using ET's and soil moisture monitoring.
"Successful irrigation management requires regular quanitative monitoring of soil water and knowledge of the field crop water use, soil water holding capacity, and crop-rooting
depth." -King and Stark, BUL789
That is what Western Ag Research specializes in. That is, using soil moisture monitoring to keep the optimum water balance in the soil profile for ideal crop production and quality. We do
irrigation scheduling using four basic formats:
Regular soil moisture monitoring.
Keeping track of evapotranspiration (ET's).
Keeping track of soil water inputs (irrigations + rains).
Keeping track of crop health and crop growth stage.
1. Regular soil moisture monitoring - Western Ag Research does different soil moisture monitoring methods for two different types of irrigation systems.
For pivots, routine soil moisture monitoring should be at least 4-5 days per week. For hand-lines, wheel-lines, or solid-sets, 3 days per week is plenty.
We use three primary methods for routine soil moisture monitoring. First, we communicate with the farmer or farm manager on what they are seeing and digging for soil moisture content in
their fields. Accurate communication between Western Ag Research and the farmer or farm manager is key to irrigation management success. Second, we use TDR soil moisture probes for our
routine soil moisture measurements. The soil moisture readings are then charted 3-5 days per week.
Third, Western Ag Research uses a stationary soil moisture system that keeps track of soil moisture and precipitation on a daily basis. This is included if the farmer requests this
service. The value of this service is that a stationary moisture sensor records the entire season, each day, and provides a graph for irrigation scheduling and record keeping.
2. Keeping track of evapotranspiration (ET's) -Western Ag Research keeps track of ET's through two methods. First, we look at the AgriMet weather
generated ET data. Second, ET is measured through soil water loss on a solid-set irrigation system. Western Ag Research uses a soil that holds about 2.00 inches in the top foot. Solid-set
irrigation frequency is mostly 5-6 days with a 7-8 hour set. The amount applied is measured with rain gauges and then we measure the water use from this solid-set on a daily basis,
usually in the evening.
3. Keeping track of soil water inputs (irrigation + rain) -Western Ag Research uses special type of rain gauges for each field that has minimal
evaporation losses. All irrigation and rain events are recorded.
4. Keeping track of crop health and crop growth stage -In August, crops start to do their own thing. Some potato fields may be healthier than others,
thus their ET rates will be different in August. Even though two fields planted just 3 days difference and side-by-side may not have the same ET based on crop health. Thus, we use crop
health as a factor in scheduling irrigations.