written by Dr. Niel Allen
Extension Irrigation Specialist
To maximize the benefits from our irrigation water the following are some water conservation practices to consider.
Cover crops require water. The water use of a cover crop can be more than 12 inches depending on planting and harvest dates, and cover crop type. Water is needed to grow all crops. Cover crops are great if you have water (precipitation or irrigation) to grow the crop. Some cover crops have a high water use efficiency (unit of yield per unit of water use) which can result in the effective use of water, nevertheless, water is still required. Cover crops can provide livestock feed, provide wildlife habitat and food, reduce nitrate leaching, increase soil organic carbon, provide a ground mulch and reduce erosion. It is generally thought that cover crops improve soil structure, increase infiltration rates, and increase water holding capacity, however, some studies did not show changes in these soil properties. Challenges include cover crop establishment and termination, costs, crop establishment in mulch, and soil moisture loss. Consider your available water and decide if a cover crop is feasible.
Fallowing conserves water but doesn’t provide a crop. Consider no-till and chemical fallow to save water. Proper tillage of fallowed land can be effective but leaves soil open to wind and water erosion. If fallowing land is used for small grains or oilseed crops, consider leaving the stubble and controlling weeds with herbicide. Weed and vegetation control is critical to preserving water.
Short-season irrigation of pasture or alfalfa conserves water. Short season irrigation is discontinuing irrigation mid-season, this is also sometimes called fallowing of forage crops. Alfalfa and pasture water use efficiency is highest in the cooler months. Alfalfa produces well in hot weather but requires more water than in cooler seasons. Grass pasture production in Utah is low during the hot summer months because most Utah pastures are cool-season grasses.
No-till or reduced tillage can conserve water. Tilling soils can bring moist soil to the surface resulting in evaporation. No-till or reduced tillage can provide a mulch to reduce soil evaporation. No-till has some of the benefits of cover crops.
Fall planted small grains for forage or grain utilizes winter and spring precipitation requiring less irrigation than spring-planted grains. Fall planted grains mature sooner than spring-planted grains, shortening the irrigation season.
Weed control conserves soil moisture in all crops. Control of weeds with herbicides reduced soil water evaporation resulting from tillage.
In summary, reduce water use by 1) only growing economically feasible crops, 2) all crops require water, 3) fallowing reduces water use, but doesn’t provide a crop, 4) reduce evaporation from soil by using no-till or minimizing the number and depth of tillage, and 5) control weeds to provide more water and nutrients for crops.