ArkValley Irrigation Grant Final Report

Home Browse Search

I I I I I I I I I I I I I I I I ~ , Techniques to provide inexpensive, accurate and detailed data for large areas have been needed to overcome these limitations for the effective diagnosis, management and monitoring of salinity conditions. Recently, two mobile systems were developed by Dr. James Rhoades and his staff at the USDA-ARS Salinity Laboratory that can rapidly measure soil salinity. One of the mobile instruments consists ofa tractor-mounted four-electrode sensor, also called a wenner- array, that measures and logs soil electrical conductivity "on-the-go", (Fig. 5). As the tractor moves along a transect, an electrical current is sent through the soil with one pair of probes while the second pair of probes measure the electrical resistance which is related to salinity (Fig. 6). Measurements are recorded automatically every second as the tractor moves at speeds ranging from three to four miles per hour. The salinity is then calculated using specialized computer software. The second mobile system consists of a remote electromagnetic instrument mounted on a spot-spray vehicle, resembling a "high-boy" sprayer or small, high clearance tractor. It has become known as the asSAuLT vehicle, (Fig. 7). The salinity sensor produces an electromagnetic field that penetrates the soil causing an electrical current flow within the soil profile. The current flow is proportional to the salinity of the soil. Salinity maps can then be developed with the assistance of computer processing. Another key to the technology is the use of the Global Positioning System (GPS). Both of these mobile instruments require the precise location of each salinity measurement. The GPS currently is comprised ofl6 radio-equipped navigational satellites circling the earth in l2-hour orbits. The receiver automatically collects simultaneous location data from at least three satellites, performs precise triangulation and calculates the exact field position of each salinity measurement. At the field site, the salinity measurement and GPS data are down-loaded to a computer and processed. From the data, the computer program pinpoints for the technician the exact points in the field that will require limited soil sampling to ground truth the salinity measurements. Typically, only four to six soil sampling sites would be required in a 60 to 80 acre field. The Natural Resource Conservation Service in Colorado is currently acquiring and developing a set of equipment and instrumentation patterned after the prototypes developed by the staff at the USDA-ARS U.S. Salinity Laboratory in Riverside, California. This project demonstration site will be used to evaluate this new technology. Once implemented it will be the first time this technology will be available to Colorado farmers in making more timely and more accurate salinity assessment for better management of irrigated soils. Surge irrigation is a relatively new irrigation technology that is now recognized as a usable practice in the Arkansas River area. Surge irrigation has been demonstrated in the USDA Patterson Hollow Hydrologic Unit Area Water Quality Project in Otero County and eastern Pueblo County. Corn yields up to 228 bushels per acre have been produced with 26% less irrigation water and 34% less runoff when compared to conventionaltimow irrigation. Salt and nitrogen loading as well as deep percolation have been significantly reduced by the use of surge irrigation in these studies. There is much need for information concerning grass mixtures and grass-legume mixtures and the management of these forages for improved yielding capabilities and economic returns. Alternative forage species could help to reduce nitrate and salt loading on the soil and in the runoff water and ground water. Alternative forage crops requiring less fertilizer and irrigation, combined with more efficient irrigation technology can reduce the amount of nitrate and salt loading, pickup and leaching. 10