|Hergert, Gary - U OF NE, SCOTTSBLUFF, NE|
|Schlegel, Alan - KSU, TRIBUNE, KS|
Submitted to: Biological Systems Simulation Group Proceedings
Publication Type: Abstract Only
Publication Acceptance Date: March 21, 2006
Publication Date: April 11, 2006
Citation: Halvorson, A.D., Hergert, G.W., Schlegel, A.J. 2006. Managing for efficient use of limited irrigation water: current practices, research needs, and potential role of models. Abstr., 36th Biological Systems Simulation Conference, April 11-13, Fort Collins, CO. Technical Abstract: Water is becoming a very valuable and limited commodity in the central Great Plains area in eastern Colorado, western Nebraska, and western Kansas. Water used for irrigation of agricultural crops is being diverted to urban use to accommodate the increasing human population along the front-range of the Rocky Mountains. Sprinkler irrigations systems have been installed in the central Great Plains to irrigate land formerly furrow irrigated or that was formerly dryland. The increased pumping of water from the aquifers and reservoirs for irrigation has caused a decline in water tables, such as the Ogallala aquifer located in the eastern part of the central Great Plains. The decline in water table level not only increases pumping and production costs, but also jeopardizes the future of irrigated agriculture in some areas. Thus, managing available water supplies for optimum yield, quality, and economic returns becomes a critical management factor for producers. With reduced water availability, the question becomes how do producers utilize a limited quantity of water to achieve the highest economic yields on his or her farm. Limited water supplies need to be applied at critical crop growth stages to optimize crop productivity and yield. Research shows that for many grain crops, water application during the reproductive and early grain fill stages is critical. There must be sufficient stored soil moisture or precipitation up to this time, however, to provide sufficient growth and yield potential to produce a crop. Thus, reducing water application during the vegetative production period of crops and applying it during the reproductive stage may be a critical management decision that will result in improved water-use efficiency (WUE). The strategy for other crops (forages, root crops, vegetables) is not certain because there has been limited research. Forage crops have a different water timing need than grain crops. Forage crops require water during the vegetative production period to optimize biomass production, thus requiring early season rather than late season application of irrigation water to optimize WUE. Research is needed to determine the effects of water stress at various growth stages on final grain, forage, or produce yield of crops grown in the central Great Plains, as well as other irrigated areas. Developing sufficient data for a wide range of irrigated conditions across the U.S. is difficult. Models have the potential to integrate the research data, extrapolate beyond specific sites, and help producers with limited water supplies make management decisions on how to most effectively utilize available water for greatest economic returns. This paper presents examples of current management practices that can be used to optimize WUE when limited water supplies are available. Halvorson et al. (Proc. Great Plains Soil Fertility Conf., 2006) compared drip vs. furrow irrigation systems for onion production near Rocky Ford, Colorado. A total of 27 inches of water was applied to the onions in 20 irrigations compared to 96 inches of water in 13 irrigations with the furrow irrigation system. Onion yields were greater with the drip irrigation system than with furrow irrigation. Application of N fertilizer increased onion yield and onion size, with the drip system producing higher onion yields with less N applied than with the furrow irrigation system. Gross economic returns, after adjusting for cost of drip system, water, and N fertilizer, were greater with the drip system at low N rates and equal to the furrow system at high N rates. This study points out that irrigation system and management of plant nutrients, especially N, can play an important part in maximizing WUE. Halvorson et al. (Agron. J. 98:63-71, 2006) showed that N fertilization rates that optimized corn grain yields also optimized WUE near Fort Collins, CO. In Nebraska, Hergert et al. (J. Prod. Agric. 6:520-529, 1993) used no-tillage cropping systems to conserve more natural precipitation, and distributed limited water supplies to irrigated crops during critical growth stages. Crops included winter wheat, sorghum, soybean and corn in different cropping systems. Annual precipitation was 19.4 inches per year. Yield averages over 10 years showed that with a 6 inch water allocation, winter wheat yields were 100%, soybean yields 92%, sorghum yields 85%, and corn yields 77% of fully irrigated crop yields. Current research at Scottsbluff, NE (15 inch annual precipitation) is comparing yields in a winter wheat-dry bean-corn rotation. In this drier, climate 8 to 9 inches of irrigation water produced near maximum yields for dry beans and winter wheat, and about 80 % of fully-irrigated corn yields. Near Tribune, Kansas, current research by Schlegel et al. (2005 unpublished data) shows that grain yields of crops receiving a limited amount of irrigation water have averaged 80 % of fully irrigated crops. Continuous corn receiving 10 inches of irrigation produced 170 bu/a (3-yr average) compared with 211-213 bu/a for corn receiving 15 inches of irrigation in a corn-wheat, corn-wheat-grain sorghum, or corn-wheat-grain sorghum-soybean rotations. Grain sorghum yields were similar in the 3- and 4-yr rotations (125 vs. 129 bu/a). Soybean yields averaged 45 bu/a. Both sorghum and soybean were limited to 10 inches of irrigation. Wheat in the rotations was limited to 5 inches of irrigation allowing an additional 5 inches to be applied to corn (all systems were limited to an average of 10 inches). An economic analysis found that profitability was similar for all crop rotations, but less than that for continuous corn. Future research needs to include: (1) more information on the effects of water stress on crop yield potential at various growth stages; (2) determining the impact of tillage system on WUE efficiency; (3) determining alternative crop rotation effects for various irrigated production areas that optimize WUE and economic returns with limited quantities of irrigation water and (4) determining how water can be spread between different crops in different cropping systems to maximize the value of irrigation water applied. Models can play a key role in helping integrate regional research data from various research projects into a management or decision aid tools that help producers make the best decisions on how to use limited water supplies. For example, Kansas has a model called “Crop Water Allocator” (http://www.oznet.ksu.edu/mil/cwa/) to help producers decide how much water should be allocated to each crop in an irrigated management unit. Kansas also has a model called “Kansas Water Budget” (Khan et al., J. Nat. Resour. Life Sci. 25:170-174, 1996) to help producers decide the most effective time to apply limited quantities of water to a crop for optimum response and final grain yield. Nebraska has developed a spreadsheet program called “Water optimizer” (http://extension-water.unl.edu) that guides producers through exercises on water allocation. Additional information is needed for other crops and climatic areas which could be addressed by models. Models can play a key role in helping producers, crop consultants, and water managers decided when to apply water and how much to make best use of limited water supplies. Models could help producers decide if one crop should receive more irrigation water than another crop in the rotation for optimizing economic returns.