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Fluid Journal : Fluid Journal 1993-1995
1 Fluid Journal Spring 1993 Table 1. Nitogen characteristics of the Nebraska MSEA site. Residual Starter Other Irrigation Irrigation Soil N* N N fertilizer Fertilizer water N** system (lb/acre) (lb/acre) (lb/acre) Method (lb/acre) 1991 Conventional 95 30 150 preplant (NH3) 269 Surge-Flow 154 30 80 sidedress (NH3) 129 Center-Pivot 85 30 0 fertigation (NH3) 97 1992 Conventional 108 19 140 preplant (NH3) 212 Surge-Flow 121 19 46 sidedress (NH3) 66 Center-Pivot 70 19 23 fertigation (NH3) 60 * Total residual N (nitrate-N) to a depth of 3 ft. ** Estimated credit for nitrate-N in irrigation water for the purpose of making fertilizer N recommendations was 69 lbs N/acre (9.5 inches average application at 32 ppm (mg/L) nitrate-N or approximately 7 lb N/acre-inch. Summary: Nitrate contamination of ground water is often attributed to the nitrogen (N) fertilizer that producers apply to crops. Efforts to minimize nitrate leaching can take many forms, de-pending on the cropping system. Management practices that improve N use efficiency by crops will be a major component of environmentally sound and profitable cropping systems of the future. The Nebraska Management System Evaluation Area (MSEA) project is an example of how N and water management practices can be modified to improve crop N use efficiency. The objective of this demonstration/research project is to develop and implement cropping systems that reduce the potential for nitrate contamination of ground water in the Platte River Valley of Central Nebraska. This project near Shelton, Nebraska, is one of five such lo-cations (Ohio, Missouri, Iowa, Minnesota and Nebraska) in the U.S. that are part of the President's Water Quality Initiative. The scope of each project and the approach taken at each location are unique because of the different climatic conditions, soil characteristics and cropping systems for the areas. Nitrogen management options avail-able to producers vary by regions, but to be practical they must be compatible with existing cropping systems. Producers with irrigation may have the opportunity to fertigate, which extends the traditional window for fertilizer applications. Dryland producers can also apply N fertilizer after sidedressing by using high- clearance vehicles (i.e. spoke injectors), but this approach is less convenient than fertigation and is plagued with the uncertainty about N availability to the roots when applied in dry soil. Drs. James S. Schepers, Darrell G. Watts and Todd A. Peterson In Search of Nitrogen Efficiency Nebraska MSEA project explores ways to improve crop N use efficiency. Irrigated corn producers who choose to rely on fertigation to apply part or all of their N fertilizer expose themselves to the risk of not needing to irrigate at times when the crop requires N. However, environmental considerations and a shift toward more automated irrigation systems (sprinkler and gated pipe with surge-flow control valves) have prompted more and more producers to consider fertigation for part of their N needs. Any discussion of fertigation requires one to consider the uniformity of water application, because an irrigation system that has poor water distribution will not apply fertilizer uniformly and could even enhance ground water contamination by nitrate. Considering the water management options available to producers, the Nebraska MSEA project was designed to compare nitrate leaching, productivity and profitability of a conventional irrigated corn cropping system with a somewhat more costly alternative using surge-flow irrigation and a more costly center-pivot irrigation system. Each of these cropping systems offers unique features that can be viewed as either an opportunity or a limitation. Fertigation is one of the primary N management options associated with irrigation systems, provided water is distributed uniformly. Therefore, fertigation was considered a viable management practice for the surge-flow and sprinkler irrigation systems above. Other management practices imposed on the cropping systems as appropriate were: Conventional Furrow • soil testing • furrow irrigation • diked-end furrows • preplant N fertilizer Surge-flow Furrow • soil testing • laser grading • runoff recovery pit • irrigation scheduling • limited sidedress N or fertigation Sprinkler • soil testing •tissue testing •fertigation • irrigation scheduling
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