Site-specific water management

Authors: Vories, Earl

Submitted to: Meeting Abstract
Publication Type: Abstract Only
Publication Acceptance Date: 11/13/2018
Publication Date: N/A
Citation: N/A

Interpretive Summary:

Technical Abstract: Mid-South fields often contain a lot of soil variability, which diminishes the effectiveness of conventional irrigation management. Guidelines for irrigation are typically linked to soil texture and in the Mid-South it’s common to have areas with different texture in the same field. Irrigation scheduling methods that assume uniform soil conditions may produce poorer than expected results on highly variable soils, contributing to a lack of commitment to irrigation scheduling by the producers even though, in general, scheduling improves overall crop production. Furthermore, if we water the whole field the same we can negate the benefits of site-specific application of agrochemicals, seeds, and nutrients. In addition, while we can measure how much water was received in a rain or applied in an irrigation, knowing how much of it reached the root zone is much more challenging and is probably not uniform over the whole field or constant throughout the growing season. Variable rate irrigation (VRI) technology provides the opportunity to address some of these problems. Center pivot systems can now operate more like a variable rate sprayer, with different application rates along the lateral, and commercial VRI systems have been shown to perform dependably. While soil texture will impact the optimal application rate for a given part of the field, it is likely that some measure of crop stress and/or soil water content will be needed to be responsive to differences among individual growing seasons. USDA Agricultural Research Service researchers at Bushland, TX, recently patented an Irrigation Scheduling Supervisory Control And Data Acquisition (ISSCADA) system that uses integrated sensor networks to detect variable crop water needs and provide site-specific recommendations for watering rates. The system is currently being tested in two Mid-South locations, with cotton at Portageville, MO, and soybean at Stoneville, MS. The crop coefficient, Kc, is the ratio of crop evapotranspiration, ETc, to a reference crop evapotranspiration, ETo. The Kc value is generally assumed to be a function of crop age or growing degree days and uniform throughout the field. However, proper use of VRI will require a more detailed understanding of the spatial and temporal variability of Kc. Furthermore, the Kc value predicts ETc under ideal conditions; however, since stresses are almost always present under field conditions, experimentally determined Kc values will be affected by those stresses, and knowing the spatial and temporal variability of the Kc observed in the field will be useful for site specific irrigation management. Canopy reflectance measurements are one method for estimating Kc values in the field and previous research indicated that irrigations scheduled with a reflectance-based crop coefficient (Kcr) were more appropriately timed than with a Kc developed under non-stressed conditions. Finally, the use of unmanned aerial vehicles (UAVs) allows us to collect a lot of information without entering the field. Using a thermal sensor can provide detailed information about crop stress for use in preparing VRI prescriptions. Whatever information we use to prepare the prescription, applying the correct amount of water to each part of the field will lead to the most efficient use of our vital water resources.