Submitted to: Proceedings of the Central Plains Irrigation Conference
Publication Type: Proceedings
Publication Acceptance Date: 2/1/2006
Publication Date: 2/21/2006
Citation: Colaizzi, P.D., Lamm, F.R., Howell, T.A., Evett, S.R. 2006. Crop production comparison under various irrigation systems. Proceedings of the Central Plains Irrigation Conference, February 21-22, 2006, Colby, Kansas. p. 189-207. Interpretive Summary: Many irrigation systems presently in use in the Great Plains are highly efficient, and enable high crop yields to be produced per unit water applied. These systems generally consist of center pivots or drip irrigation. For center pivots, irrigation water is applied just over the crop (spraying) or applied in precise locations between crop rows with flexible hoses (called drag socks). Drip irrigation consists of flexible tubing buried just below the surface, and water is dripped from the tubing into the soil through plastic emitters, where it is taken up by the crop roots. We reviewed published studies on crop productivity comparisons between different systems. Most comparison studies were conducted over a range of irrigation rates from dryland (no irrigation) to full irrigation (applying as much water as the crop will use). Irrigation rates less than full irrigation are generally referred to as deficit irrigation. For most major irrigated crops in the Great Plains (corn, cotton, grain sorghum, winter wheat, soybean, sunflower), surface drip irrigation (SDI) resulted in greater crop yields under deficit irrigation, but spray irrigation slightly outperformed SDI under full irrigation. Data is presently lacking that would conclusively explain why these differences in crop yield occur, but we offer several hypotheses. Under deficit irrigation, the crop can use scarce water more efficiently with SDI than with spray because soil water evaporation is virtually eliminated. Since SDI practically eliminates soil evaporation for most irrigation rates, we think that under full irrigation, SDI may be concentrating too much water in the plant root zone, resulting in poor aeration or leaching of nutrients. Any of these factors could result in yield reduction. These studies point to the need for careful irrigation scheduling and for additional research that will increase our understanding of soil water and plant processes for different irrigation systems, so that water resources may be used most efficiently.
Technical Abstract: Studies on crop productivity for major irrigated crops in the Great Plains were reviewed for different types of modern pressurized irrigation systems. Crops included corn, cotton, grain sorghum, winter wheat, and preliminary data on soybean and sunflower. Irrigation systems consisted of spray and low energey precision application (LEPA) devices commonly found on center pivots, and drip irrigation (usually SDI). Spray, LEPA, and SDI were compared at Halfway and Bushland, TX, and simulated LEPA and SDI were compared at Colby, KS. Nearly all studies involved varying the irrigation capacity (fixed application per unit time) or irrigation rate (percentage of soil water replenishment). Yield response in terms of irrigation method could usually be described as SDI>=LEPA>=SPRAY for low irrigation capacities (or rates), and SPRAY>=LEPA>=SDI for full (or nearly full) capacities or rates. In some cases, yield response was more consistent across irrigation rates. Although additional data are lacking that would explain these differences, it appears that LEPA, and to a greater extent SDI, result in greater partitioning of water to plant transpiration relative to spray for low irrigation rates. At greater irrigation rates, the yield depressions observed for SDI and/or LEPA relative to spray were less clear, although these may be the result of poor aeration and nutrient leaching by deep percolation.