Site-specific Irrigation Through the Use of Innovative Technologies
Over the past 50 years, the goal of center pivot and linear move irrigation design engineers has been to have the most uniform water application depths possible along the entire length of the lateral pipe, and they have been relatively successful. However, the terrain under these types of irrigation systems is often quite variable, causing system pressure (and water distribution) fluctuations along the lateral pipeline. Intermittent end gun operations also cause system pressure fluctuations that end up resulting in uneven water applications. While engineering solutions such as flow control nozzles or pressure regulators at each head have somewhat helped this situation, they are still not able to fully compensate for the effects of system pressure changes (Evans et al., 1995; James, 1982; and Duke et al., 1997, 2000). These factors not only affect the amount of water applied to a given area within the field, but they also greatly compound environmental risk when applying agrochemicals through the irrigation system. If fertigation is used or if the water supply contains significant nutrients, then the nutrient distribution will also not be uniform (Evans et al., 1995; Duke et al., 2000).
In addition, soils are heterogeneous (chemically & physically) and water-holding capacities are not uniform across fields (Burden and Selim, 1989; Agbu and Olson, 1990; McBratney and Webster, 1983; Han et al., 1993). Consequently, even with relatively uniform applications, surface runoff or ponding can occur at the lower elevations. Shallow subsurface water transport along soil compaction layers and within-field surface runoff from higher elevations also contribute to saline seeps, nutrient leaching, and soil erosion (Han et al., 1996a, 1996b; Howell et al., 1995; Suddeth et al., 1996). The net result of these factors is a considerable variation in yield and agrochemical leaching across the field as well as reduced crop quality and higher pumping costs for unneeded water (Evans and Han, 1994; Han et al., 1995; Mulla et al., 1996; Mallawatantri and Mulla, 1996).
One possible solution is the development of site-specific irrigation technologies that can compensate for changing system pressures, heterogeneous soils and variable topography by applying water much more precisely to specific areas of a field. Center pivot and linear move irrigation systems are particularly amenable to site-specific approaches because of their current level of automation and the large area covered by a single lateral pipe. These types of irrigation systems provide a high level of water control and can also serve as a sensor platform for real-time water applications.
Automated, real-time irrigation technologies also make variable rate agrichemical and water applications possible. In fact, several innovative technologies have been developed to variably apply irrigation water for whole field management under self-propelled systems. Most of these approaches use standard, off-the-shelf components with the research effort directed towards developing appropriate control algorithms (Roth and Gardner, 1989; McCann et al., 1997; King and Wall, 1997; Camp et al., 1996; Sadler et al., 1996; King and Kincaid, 1996; Fraisse et al., 1992; Evans et al., 1996a; Duke et al., 1998; Harting 1999). Anticipated benefits of these systems are many including the ability for an irrigator to meet the specific needs of a crop in each unique zone within a field, which can optimize crop yield, crop quality, and maintain environmental health (water conservation and reduced agrichemical use) while reducing costs.
Activities of plant pathogens are influenced to a great extent by environmental factors such as temperature and humidity. Leaf spot caused by Cercospora beticola Sacc. is the most important foliar disease of sugar beets. The disease is a serious problem in the Northern Plains including Eastern Montana and Western North Dakota. The pathogen survives on infected beet residue as stromata (Vestal, 1933). Under optimal conditions, characterized by relatively high humidity (90-95%) and temperatures (25-35°C; above 16°C in the night), sporulation, germination and penetration occur to initiate Cercospora leaf spot disease in sugar beets (Ruppel, 1986). As an integral part of developing accurate irrigation technologies for the Northern Plains, we intend to apply recently developed DNA technology (Lartey et al., 2003) to compare the incidence of diseases under various irrigation systems. Considering the potential for disease incidence, the information will enable us to select the best irrigation system.
Contributing Scientists: Robert Evans (Agricultural Engineer), Jed Waddell (Soil Scientist), Robert T. Lartey (Plant Pathologist), Bill Iversen (Physical Scientist), James Kim (Post Doctoral Research Associate), Jay Jabro (Soil Scientist) and Bart Stevens (Agronomist)