Maximizing Alfalfa Irrigation Efficiency

A variety of irrigation management practices prove effective in utilizing water supplies more efficiently and enhances production yield potential.

The arrival of spring marks the beginning of another growing season for alfalfa growers in many parts of the country. Geography, topography, climate and soil types aside, all alfalfa growers face a variety of irrigation-related challenges, whether they use a sprinkler irrigation system or subsurface drip irrigation.

“Alfalfa and forage growers from all areas of the country are looking for effective irrigation management strategies to maximize water use efficiency without sacrificing yields,” said Dan Putnam, Extension Specialist and Agronomist with the University of California Davis (UC-Davis) Department of Plant Sciences. “Every growing season is different, as is each field. Early spring moisture and climate conditions vary from year to year, creating a new set of annual growing season challenges for producers, especially for those located in geographic regions most prone to drought and moisture deficit situations, and where precious water supplies are limited and costly.”

Water is considered by many to be the most precious and heavily scrutinized natural resource, particularly in the arid West regions of the United States. Because alfalfa requires a significant amount of water due to its long growing season, deep root system and dense canopy of vegetation, growers are often caught in the cross-hairs as regulators and environmental conservationists search for new sources to satisfy urban demand, while also serving the critical needs of agriculture.

"Once the amount of water applied with the current system is quantified, alfalfa growers can devise an effective plan for improving irrigation water management."
In California, for example, nearly 20 percent of all irrigation water used in the state is applied to alfalfa fields. This doesn’t imply, however, that alfalfa irrigation is a “water waster.” On the contrary, compared with other agricultural commodities, irrigating alfalfa is actually a fairly efficient use of H2O. Still, growers may consider a number of systems or methods to optimize water efficiency.

First things first — take accurate measurements to determine water use needs. The amount of water needed for alfalfa production is a function of temperature, wind, humidity and the amount and intensity of light. Common water use requirements for alfalfa range from 20 to 46 inches of water per season, depending on climate, elevation, growing season, number of cuttings and the fall dormancy rating of the alfalfa variety.

According to Putnam, irrigation water management cannot be improved unless alfalfa water needs are determined early in the growing season and the amount of water being applied can be accurately anticipated and measured. These two pieces of information are critical regardless of the type of irrigation system utilized. But just as each year presents new challenges, measuring the applied water can also be a challenge, especially if water is delivered in a ditch or canal.

“Accurately knowing how much water is being applied is critical for a couple of reasons,” Putnam said. “First, comparing applied water to actual water use provides growers with a good idea of how much water could be saved. Second, if alfalfa growers should decide to switch irrigation systems, it’s important for them to know how much water was applied using the former approach compared to the new irrigation system to assess potential water use reductions and efficiencies. Equally important is determining when and how much water to apply. Alfalfa irrigation scheduling is most frequently determined by diligent and accurate monitoring and estimating evapotranspiration (the process by which water is transferred from the land to the atmosphere by evaporation from the soil and other surfaces and by transpiration from plants).”

“Once the amount of water applied with the current system is quantified, alfalfa growers can devise an effective plan for improving irrigation water management,” said Putnam. “If the correct amount of water is already being applied to match evapotranspiration, water will not be saved by changing the irrigation system or management practices. Yet, it may still be possible to increase yield and alfalfa quality by changing to sprinkler or drip irrigation methods that apply water more frequently, potentially decreasing water stress. That’s why accurate and diligent moisture monitoring information is so important.”

Drought conditions present additional challenges. In areas most prone to drought of deficient moisture conditions, there are several production strategies alfalfa growers can employ to preserve alfalfa stands for future growing seasons. The ability of alfalfa to go dormant during extended dry periods when water is not readily available makes it one of the few crops that can recover once adequate precipitation or irrigation occurs. As long as plant roots remain viable (white, moist and pliable) the alfalfa plant itself has a good chance to recover and survive.

Cutting management is the primary control for increasing stand during periods of drought. Harvest frequency will not only determine alfalfa persistence, but also the quality of the crop. Cutting during drought management is similar to dormancy management. Therefore, alfalfa growers need to keep enough top growth to maintain the plants vitality and retain healthy stands. If the crop is cut during drought conditions, top growth of at least six to eight inches should be maintained which allows continued root and plant functioning so that the alfalfa can persist through the fall and winter months. If enough top growth is available to make cutting economical while maintaining height as the plant enters dormancy, cutting can be managed based on when harvesting is the least stressful to the plants.

If water is available, summer irrigations should occur between cuttings and be applied immediately after the crop is removed from the field, generally within 10 to 15 days after cutting. This allows for continued root development even under the stress inflicted by drought conditions. In situations where district irrigation water or the more salty shallow well water is not available, plant heights of between six and eight inches should be maintained to allow plants to enter dormancy. Later rains may revive the plants prior to the arrival of cooler fall and winter temperatures, but if not, the top growth may help plants survive through the drought period and into winter dormancy.

To retain crop persistence in alfalfa during drought years, it’s important for growers to consider key management—cutting management, irrigation (if available), insect control and fertilization—to optimize drop maintenance and growth during drought periods. Alfalfa producers should be aware, however, that deficit irrigation imposed after the first cutting is likely to reduce yields of future cuttings, especially if no irrigation is available.

 

Common Alfalfa Irrigation Systems:

Sprinkler irrigation is very common, most notably on fields that are not easily leveled. A well-designed sprinkler irrigation system should be capable of high irrigation efficiency with little runoff. The two most common issues impeding efficiency are poor management and inadequate maintenance. It’s important for growers to accurately match irrigation water applications to the specific needs of a field, while inadequate maintenance will be evident by sprinklers not delivering water properly or the presence of leaks created by replacement sprinklers that do not match the original design.

 

 

 

 Drip irrigation, while not yet common, is being used more frequently as water cost and scarcity of supplies increase. Drip irrigation is almost exclusively subsurface drip irrigation in which drip tape is placed below ground at various spacing and depths. The depth of tape placement is dependent on the ability to irrigate the crops, installation issues and the requirement to do field cultivation or other cultural practices above the tape. A well-designed drip irrigation system can be highly efficient, but it is also an expensive system to install and maintain.

 

 

 

Want more? Check out these Irrigation Strategy Recommendations.

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