Over the last several years, agricultural producers have been pulled in multiple directions: improve water use efficiency, maintain profitability in the face of rising input prices, and improve sustainability and soil health. But what if these objectives didn’t need to be competing?
In the western United States, the summer of 2021 will be remembered as one of the driest and hottest years on record. It has become increasingly apparent that agriculture is under more and more pressure to produce crops with less irrigation water. This is driven by several factors: a series of below-normal irrigation water supply years, a series of higher-than-normal crop water use years, and increasing demand for limited water resources. These past few years of water supply challenges may be a preview of more serious conditions to come. Although the timing and severity of water supply reduction will vary with location, general trends indicate that future supplies will be limited to some degree. Therefore, adoption of changes in irrigation and soil management that conserve water while maintaining crop yield and quality will help minimize the long-term impact on irrigated agriculture.
Relationship Between Water and Soil Health
The technical definition of soil health is the continued capacity of the soil to function as a vital living system, within ecosystem and land-use boundaries; to sustain biological productivity; promote the quality of air and water environments; and maintain plant, animal and human health. But what does this mean for an individual producer? It’s almost a guarantee that if 100 growers were asked what soil health meant to them, there would be at least a dozen answers. This is where goals become important. Without soil health goals, it’s almost impossible to assess progress and impact of implemented practices. Some examples of goals growers might have are: increase soil organic matter; reduce fertilizer inputs; or improve water infiltration or water use efficiency.
For all three example goals, water can be, is, and should be a key component. Without water, provided either through rainfall or irrigation, soil biology cannot thrive. Soil fauna, just like humans, need water to reproduce and function. One of the key functions of soil biology is nutrient cycling through the consumption and creation of soil organic matter as well as plant and animal residues. Some soil organisms help “glue” soil mineral particles together through byproduct production, while other soil organisms “tie” particles together with hyphae. Both processes help improve soil structure by creating more space for water and air exchange, which improves water infiltration. In sum, improved water management improves soil health and improved soil health improves water management.
Tips for Improving Water Management
Water delivery to the crop can be improved by regularly maintaining and replacing worn sprinkler nozzles. Data from several University of Idaho assessments of irrigation systems has shown that incorrectly sized or worn-out nozzles on any type of irrigation system (handline, wheel line, pivot) can result in 10 to 15% more water being applied than necessary. The overall life expectancy of nozzles depends on several factors but can generally be expected to maintain good efficiency for five to seven years. Surface water that contains silt can reduce life expectancy; groundwater sources generally don’t have this issue. Regardless, nozzles should be inspected every year for wear and tear and replaced when necessary. Leaks can cause an additional 10 to 35% excess water application.
Growers should consider ways to capture more winter moisture like reducing or eliminating fall tillage. Maintaining crop residues through the winter can help increase spring soil moisture 5 to 15% over fall-tilled ground by capturing more snow. This moisture head start over bare ground can reduce spring irrigation needed to fill the soil profile and provide a buffer if irrigation supply is limited or if the irrigation system cannot keep up with crop evapotranspiration.
New technology like soil moisture sensors or an irrigation water scheduling assistant should also be considered. Soil moisture sensors can be a valuable tool for making irrigation scheduling decisions based on crop and soil conditions rather than a set weekly schedule. Sensors can also highlight ways irrigation management can be improved. For example, soil moisture sensors deployed in six locations across a wheel line-irrigated field showed that there were significant differences in water applied across the season (8 inches difference). By using data like this, in-season management decisions can be tailored based on weather conditions and crop conditions.
Free irrigation schedulers are also available that use local weather data and crop water needs to help make irrigation timing decisions.
Linda Schott is a soils and nutrient management extension specialist at the University of Idaho’s Twin Falls Research & Extension Center. She can be contacted at lschott@uidaho.edu.
Howard Neibling (hneiblin@uidaho.edu) is an extension water management engineer based at the UI Kimberly Research & Extension Center.