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Alfalfa provides high-energy feed for dairy cows and other livestock. This crop is also known for its high water-use efficiency. Subsurface drip irrigation (SDI) is an ideal method for meet...

The Alto Rio Lerma Irrigation District, located in the state of Guanajuato in Mexico, is an agricultural area whose sustainability depends partially upon groundwater withdrawal for crop irrigation. Because of high pumping demands and current land-management practices, groundwater levels have declined severely, resulting in aquifer overdraft. In order to analyze economic, environmental, and water use problems in this region, 12 potential cropping patterns were generated for different groundwater withdrawals using linear programming. Then, simulation of the agricultural system was performed using GLEAMS to estimate the amounts of water, nitrate, and pesticides in both runoff and percolation for each cropping pattern. Pumping costs and an aquifer exploitation coefficient account for the economic and environmental impacts of aquifer overdraft. Finally, the Range of Value Method (multicriteria method) was applied to rank and identify the best cropping pattern. The results show the best alternative for effectiv...

A key component in the calculation of reference crop evapotranspiration (ETr) is the weather data. If the weather data have been collected from a station under nonreference conditions, the data itself may contain errors, which will in turn yield inaccurate ETr estimates. It was proposed by Allen in 1996 that data used for evapotranspiration be scrutinized by comparing daily minimum temperature (Tmin) and the daily average dew point temperature (Tdew). If the difference between Tmin and Tdew is greater than 3°C, then the site is considered to be arid (nonreference) and adjustments are recommended for temperature and dew point data. In Arizona, normal weather conditions often occur where Tmin and Tdew do not approach each other. This study examined the appropriateness of applying the conditions set forth by Allen to temperature data collected in central Arizona. Two weather stations were set up in a 35.5ha alfalfa field in central Arizona to measure dry bulb and wet bulb temperatures. Additionally, plant te...

Contamination of surface and subsurface waters has become a major problem related to agricultural practices. Nitrate, one of the principal plant fertilizers, is the chemical having the greatest effect. This research utilized closed system laboratory experiments to evaluate the effectiveness of an electrokinetic process in concentrating and retaining nitrates close to the anode and studied the effect of selected electrokinetic system design parameters on the performance of the process. The tests demonstrated that an electrokinetic process can effectively concentrate and retain nitrate close to the anode in saturated sandy soil.

Chemicals applied to agricultural lands inevitably move below the plant root zone and may contaminate the underlying ground-water reservoirs. Laboratory open system soil column experiments were conducted to evaluate electromigration as a process for concentrating and retaining the nitrates close to the anode in soil subjected to hydraulic flow. Electromigration was found to be an effective means for concentrating and retaining nitrate close to the anode in saturated sandy soil at low flow rates. However, for a given electrical input, the effect was reduced as the hydraulic flow rate increased, being indiscernible for higher flow rates.

A framework for determining the effect of maintenance events on irrigation system flows is described. Standard definitions for corrective and preventive maintenance are presented and two maintenance objectives and six classifications are established. Maintenance activities and decision criteria common to many irrigation systems are suggested. A format for describing these and other maintenance activities is proposed. A methodology for setting decision levels for maintenance activities is presented. Maintenance cost is compared with income lost as a result of less than maximum production because water supplied was insufficient for crop requirements. This comparison demonstrates that maintenance decision levels should be set so that maximum evapotranspiration can be achieved. Budget request forms and report forms are presented with examples of actual maintenance events showing the expected and actual impact on system flows.

This paper describes a simple, few-parameters simulation model for a water harvesting-strip farming system. The model includes runoff threshold functions for different soil types, and for different initial soil water contents. The evapotranspiration component of the model accounts for dynamic root water extraction using regression equations that correlate canopy cover with root growth as a function of time. The model is simple to operate and uses readily available inputs. It can work with several crops when leaf area indices and crop stage coefficients are provided. The agreement between simulation outputs and field-observed data indicates that the model accurately describes the water balance within the system. The model is then recommended for obtaining preliminary design of water harvesting systems. A FORTRAN77 source code has been written for the simulation procedure.

Migration of chemicals in soils to surface or ground water has become a serious threat in many agricultural regions, with nitrates affecting the broadest area due to intensive fertilization and nitrate solubility. This project evaluated electroreclamation utilizing subsurface horizontal drainage tubing and parallel electrodes to concentrate and remove nitrates from soil. Nitrate concentration in saturated soil tended to increase from anode to cathode after the application of a small direct-current electrical field as the nitrate solution moved toward the cathode. When soil moisture content dropped below the saturation level, the nitrate began to migrate toward the anode. Research is recommended to evaluate the effect of a broader range of electrical parameters and analyze the feasibility of commercial application.

A significant advantage attributed to surge flow irrigation is that for the same volume of water applied the stream will advance farther along the furrow than with continuous flow. Where this advance phenomenon exists, the reduction in runoff and deep percolation will improve uniformity and application efficiency. The mechanism for improvement in advance time has generally been ascribed to surface sealing and surface layer consolidation. However, these phenomena do not satisfactorily explain improved advance times in sandy soils. The Green‐Ampt model combined with a simple redistribution model is used to illustrate the effects of reduced wetting front suction due to intermittent wetting on the instantaneous infiltration rate on two soils. The effect of various surge cycle times on the volume infiltrated versus time is also predicted by the model. This approach to modeling infiltration under surge irrigation shows considerable potential for determining the effect of surge irrigation on a range of soil text...