The dictionary definition of fate is “the development of events beyond a person’s control, regarded as determined by a supernatural power.” When it comes to determining how much of your crop actually receives the water you provide it, sometimes it can seem rather mysterious what goes where.

Discussing “the fate of drip irrigation water” at the most recent Great Lakes Expo was Michigan State University Extension Agriculture Water Use Efficiency and Irrigation Educator Brenden Kelley. His goal was to help growers take more control over this resource and use it more successfully.

One of the first things those using drip irrigation need to consider is the vertical and lateral movement of water once it hits the ground. Heavier soils mean slower infiltration. They tend to create a wider “plume” of an irrigated area within the soil.

Coarser soils mean faster infiltration. They tend to create a deeper plume of irrigated soil. The soil’s texture determines the path of flow as well as its water-holding capacity.

Next, really think about depth. The maximum irrigation depth needs to equal the maximum rooting depth of the crop being grown. For example, apple trees have a maximum rooting depth of 48 inches; corn, grapes and asparagus, 36 inches; blueberries, 24 inches; carrots, 12 to 36 inches; and broccoli, 18 inches. Is your water penetrating that deep?

And remember that a plant’s growth stage also influences root depth and transpiration rates.

Where irrigation ends up has several factors, according to Kelley. These include the flow rate, emitters per plant, the application area, plant and row spacing, remaining soil moisture, soil type and duration.

This can all be condensed into three questions to be answered: How much water needs to be applied? How big is the area you’re applying to? And how much can the root zone receive? How much you need to apply should be based on scheduling, plant size and rooting depths.

You may also think more irrigation is better, but be careful that your emitters aren’t spaced too close together. “More emitters can be a detriment because they increase off-target application and there will be less incentive for roots to grow deeper,” Kelley said. (This is less of a problem in a bed or row with 100% coverage.)

Growers should aim to apply a volume of water that reaches the lower range of plants’ root zone. Try to direct the application directly to the soil – this will result in minimal loss (aka the “application tax”).

If your current rate can’t keep up with evapotranspiration, consider adding more lines. For example, for a one-inch application to the crop’s area, the depth applied to the application radius equals 31 inches for one emitter per plant or 15 inches for two emitters per plant.

For those looking for additional help steering the fate of their drip irrigation water, Kelley suggested looking into USDA-NRCS’s 449 Irrigation Water Management (IWM) program. The 449 program includes financial assistance for developing and maintaining irrigation records as part of an IWM plan, and for the purchase of IWM devices like soil moisture sensors. Most IWM plans have included the use of soil moisture sensors.

Other conservation incentive contracts practices and enhancements offered by USDA include 441 (Irrigation System, Microirrigation) and 442 (Sprinkler System). Reach out to your NRCS contacts to see if any of these programs may benefit your operation.

by Courtney Llewellyn