James R. Gilley

sprinkler Droplet Size Distribution Estimation from Single Leg Test Data

ABSTRACT DROPLET size distribution data from agricultural sprinklers are useful for predicting evaporation, wind drift, and droplet effects on the soil. Collecting droplet size distribution data is tedious and expensive, so a method of estimating such data from existing or routinely collected data would be useful. The theory and technique for estimating such data using droplet ballistics are described whereby droplet size data can be estimated from routinely collected single leg data. The model was tested for five sets of conditions including three nozzle sizes and three pressures and proved to fit published droplet size data very well. The distributions produced by the estimation technique are presented.

Simulation of the soil-water dynamics and corn yields under deficit irrigation

SummaryA simulation model capable of predicting the yield response of corn to a limited water supply was developed by combining two existing mathematical models. The resulting computer model was evaluated using experimental data taken under a wide range of soil moisture conditions. The soil profile water balances was simulated using SWATRE and SUCROS was used to model the crop growth in response to environmental conditions. In addition to the integration of the two existing models, some minor changes were made to each in an effort to improve the accuracy of the combined models. The model input parameters were derived entirely from published literature. The experimental data necessary for model validation were available from irrigation studies at the Sandhills Agricultural Laboratory of the University of Nebraska. These experiments not only provided the required input soil and climatic data, but also the observed irrigation levels, soil moisture distributions and crop yield required for model validation. Initial evaluation of the computer model indicates that the combined model adequately describes crop evapotranspiration, soil moisture extraction and crop yield under a fairly wide range of soil moisture stress. Additional modifications for the prediction of leaf area expansion and senescence, especially under moisture stress, are needed to improve the accuracy of the model.

Economic Analysis of Energy Saving Practices in Irrigation

ABSTRACT THE economic benefits of various energy saving practices for both gated-pipe surface irrigation systems and center-pivot sprinkler irrigation systems were evaluated for several initial operating conditions. The analysis included the energy savings resulting from a particular irrigation system improvement and the costs associated with that improvement. The order of economically beneficial changes for gated-pipe systems was: (a) pumping plant adjustment, (b) irrigation water management and (c) irrigation application efficiency improvements. For center-pivot systems the order was; (a) pressure reduction, (b) pumping plant adjustment, (c) irrigation water management and (d) irrigation application efficiency improvments

An experimental center-pivot irrigation system for reduced energy crop production studies.

ABSTRACT AN experimental 52.6 ha center-pivot irrigation system for studies of reduced energy crop production systems is described. The system consists of high pressure impact sprinklers, low pressure impact sprinklers, and low pressure spray nozzles that are automatically turned on or off at preselected locations in the field. The control procedures ofthe system operation are described. The system also has the capability of applying different depths of water per irrigation as a function of position radially outward from the pivot point. Four years of data indicate that the system controls function properly and the design irrigation depths are being met. The concept of rotational uniformity or the spiking of water application as the pivot rotates is presented. Field measurements of water distribution of the different sprinkler packages indicate that rotational uniformity appears to be a problem only on the spray nozzle system and only for those systems applying relatively small application depths. The low pressure spray nozzles have the lowest uniformities while the high pressure impact and low pressure impact sprinklers have nearly identical uniformities.

Potential use of wind power for pumping irrigation water

Abstract The potential energy savings from three types of wind powered irrigation pumping plants were determined for selected areas of the U.S.A. The wind systems analyzed were: wind assist combustion engines; wind assist electric motors, with and without the sale of surplus electricity; and a stand-alone turbine with a reservoir for water storage. Because of the reduced wind power available and the relatively short time span during the irrigation season, the wind assist turbines will only provide between 6 and 31% of the required energy for pumping water. In all regions, the amount of electrical energy available for sale from the wind assist system is greater than the energy saved. The stand alone turbines can provide all the energy required for pumping the irrigation water; however, their use will require the installation of a reservoir for water storage. Thus, the stand-alone systems are suitable only in locations where surface irrigation systems can be used or where other energy sources can be used to pressurize the water distribution system. The size distribution of the on-farm irrigation pumping plants in the U.S. for zones of similar average wind power during the principal irrigation season is presented. The mid and southern Great Plains areas which have the largest potential wind power during the primary irrigation season account for over 32% of the nations pumping units.

Irrigation System Capacities for Corn Production

ABSTRACT IRRIGATION system capacity requirements for corn production in Nebraska were determined using a computer simulation model. A daily water balance was used to calculate moisture depletions and ultimately, to estimate the amount of transpiration by the crop. Yield reductions were estimated using the ratio of the seasonal crop transpiration to the potential seasonal transpiration for a crop without water stress. Using the daily soil moisture depletion and seasonal yield reduction data, histograms and cumulative density functions of soil moisture depletion and crop yield reduction were developed for various soils, locations and system flow rates. Graphical relationships between soil moisture depletion and system capacity and between crop yield reduction and system capacity were developed. The yield reduction-system capacity relationships developed were dependent upon the type of irrigation management strategy employed and the soil type. Four sites in Nebraska were studied, and system capacity recommendations for two sites were chosen as representative of the climatic variability across the state.

ENERGY REDUCTION THROUGH IMPROVED IRRIGATION PRACTICES

Several methods are presently available to reduce the energy required to pump water for irrigation, including: increased water use efficiency; increased pumping plant efficiency; irrigation scheduling; and reduced pumping pressures. The cost of electricity for pumping can be reduced further by scheduling pumping during times other than the period of peak demand on the utility system. An additional energy saving from improved water management is achieved through a reduction in losses of nitrogen fertilizer by leaching.

Size Distribution of the On-Farm Irrigation Pumping Plants in the U.S.

ABSTRACT OVER 473,000 on-farm pumping plants were used to pump and deliver irrigation water in the United States in 1979. Over 60 percent of these units were smaller than 37.3 kW (50 hp) and only 9 percent of the units were larger than 74.6 kW (100 hp). Nearly one-half of the pumping plants (231,440) were located in the six High Plains States of Colorado, Kansas, Nebraska, New Mexico, Oklahoma and Texas.