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Recent ERS Research on Nutrient Management (cont.)

An Economic Analysis of Agricultural Practices Related to Water Quality: the Ontario (Oregon) Hydrologic Unit Area. ERS Staff Report No. AGES-9418. June 1994 (C. S. Kim, Ronald Fleming, Richard M. Adams, Marshall English, and C. Sandretto). This report evaluates the effects of adopting Best Management Practices (BMPs) on groundwater quality in Ontario (Oregon) area by incorporating time lags associated with nitrate leaching and groundwater flow. Results indicate that Federal drinking water standard of no more 10 ppm nitrate in groundwater may be accomplished in 12 years by adopting improved irrigation systems such as auto-cutback systems or solid-set sprinkler systems. However, the adoption of both improved irrigation systems and nutrient management systems, such as sidedressing and ceasing fall fertilization, would be necessary to meet the strict Oregon drinking water standard of 7 ppm. "The Role of Information in the Adoption of Best Management Practices for Water Quality Improvement." Agricultural Economics, No. 11 April 1994. (Peter M. Feather and Gregory S. Amacher). This paper tests the hypothesis that a lack of producer information regarding both the profitability and the environmental benefits of adopting improved practices may be a reason why widespread adoption of these practices has not occurred. A two-stage adoption model is specified and estimated using data from a survey of producers. The results indicate that producer perceptions play an important role in decision to adopt. Changing these perceptions by means of an educational program may be a reasonable alternative to financial incentives.

Timing Nitrogen Fertilizer Applications to Improve Water Quality. ERS Staff Report No. AGES-9407, February 1994 (Wen-yuan Huang, Noel D. Uri, and LeRoy Hansen). Analytical models are developed to determine the necessary conditions for the optimal timing of nitrogen fertilizer application. The empirical results explain various observed timings of nitrogen fertilizer application to cotton in Mississippi, and provide an estimate of a farmer's cost in complying with a restriction on the timing of nitrogen fertilizer application.

(Contact to obtain reports: Wen-yuan Huang, (202) 501-8289 [whuang@econ.ag.gov])

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PRODUCTION MANAGEMENT

4.6. Irrigation Water Management

Water management is an important element of irrigated
crop production. Efficient irrigation systems and water
management practices can help maintain farm profitability
in an era of limited, higher-cost water supplies. Efficient
water management may also reduce the impact of irrigated
production on offsite water quantity and quality. However,
measures to increase water-use efficiency may not be
sufficient to achieve environmental goals in the absence of
other adjustments within the irrigated sector. As is often
the case, technology is not the whole solution anywhere,
but part of the solution almost everywhere.

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percolation to saline formations, and greater instream pollutant concentrations due to reduced flows. Strategies to improve the Nation's water quality must address the effect of irrigation on surface and ground water bodies (National Research Council, 1996).

Farm Returns. Finally, improvements in IWM can help maintain the long-term viability of the irrigated agricultural sector. Irrigated cropland is important to the U.S. farm economy, accounting for about 40 percent of total crop sales with just 15 percent of the Nation's harvested cropland in 1992 (USDC, 1994). Water savings at the farm level can help offset the effect of rising water costs and restricted water supplies on producer income. Improved water management may also reduce expenditures for energy, chemicals, and labor inputs, while enhancing revenues through higher crop yields and improved crop quality.

Use of Improved Irrigation Technology and
Management

How producers respond to higher water costs and
limited water supplies is important to policymakers.
Producers may reduce water use per acre by applying
less than full crop-consumptive requirements (deficit
irrigation), shifting to alternative crops or varieties of
the same crop that use less water, or adopting more
efficient irrigation technologies. In some cases,
producers may convert from irrigated to dryland
farming or retire land from production. Many
irrigators have responded to water scarcity through
the use of improved irrigation technologies-often in
combination with other water-conserving
strategies and irrigators will likely look to
technology as one of several means of conserving
water in the future.

Various management practices and irrigation technologies are available to enhance efficiency of applied water in irrigated agriculture (see box, "Irrigation Water-Use Efficiency"). Irrigation improvements often involve upgrades in physical application systems, with improved field application efficiencies and higher yield potentials. Improved water management practices, such as irrigation scheduling and water-flow measurement, may also be required to achieve maximum potentials of the physical system. In addition, management of drainage flows may be an important concern in many irrigated areas (table 4.6.1). In some cases, the effectiveness of improved irrigation practices may be enhanced when implemented in combination with other farming practices such as conservation tillage and nutrient management.

Irrigation Water-Use Efficiency

Water-use efficiency measures are commonly used to characterize the water-conserving potential of irrigation systems. Alternative efficiency measures reflect various stages of water use and levels of spatial aggregation. Irrigation efficiency, broadly defined at the field level, is the ratio of the average depth of irrigation water beneficially used (consumptive use plus leaching requirement) to the average depth applied, expressed as a percentage. Application efficiency is the ratio of the average depth of irrigation water stored in the root zone for crop consumptive use to the average depth applied, expressed as a percentage. Crop-water consumption includes stored water used by the plant for transpiration and tissue building, plus incidental evaporation from plant and field surfaces. Leaching requirement, which accounts for the major difference between irrigation efficiency and application efficiency, is the quantity of water required to flush. soil salts below the plant root zone. Field-level losses include surface runoff at the end of the field, deep percolation below the crop-root zone (not used for leaching), and excess evaporation from soil and water surfaces. Conveyance efficiency is the ratio of total water delivered to the total water diverted or pumped into an open channel or pipeline, expressed as a percentage. Conveyance efficiency may be computed at the farm, project, or basin level. Conveyance losses include evaporation, ditch seepage, operational spills, and water lost to noncrop vegetative consumption. Project efficiency is calculated based on onfarm irrigation efficiency and both on- and off-farm conveyance efficiency, and is adjusted for drainage reuse within the service area. Project efficiency may not consider all runoff and deep percolation a loss since some of the water may be available for reuse within the project.

Irrigation Application Systems

Irrigation application systems may be grouped under two broad system types: gravity flow and pressurized systems. (For an explanation of irrigation systems discussed here, see boxes, "Gravity (Pressurized) Irrigation Systems and Practices," pp. 229-230.)

Gravity-Flow Systems. Many irrigation systems rely on gravity to distribute water across the field. Land treatments such as soil borders and furrows-are used to control lateral water movement and channel water flow down the field. Water is conveyed to the field by means of open ditches, above-ground pipe (including gated pipe), or underground pipe, and released along the upper end of the field through siphon tubes, ditch gates, or pipe valves. Fields are

Table 4.6.1-Irrigation technology and water management: conventional methods and improved practices

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