Integration of Hydrogeophysical Datasets for Improved Water Resource Management in Irrigated Systems

Water scarcity is predicted to be the major limitation to increasing agronomic outputs to meet future food and fiber demands. With the agricultural sector accounting for 80 – 90% of all consumptive water use and an average water use efficiency (WUE) of less than 45%, major advances must be made in irrigation water management. Precision agriculture, specifically variable-rate irrigation (VRI) and variable-speed irrigation (VSI) systems, offers the technologies to address and manage for infield variability and incorporate that into management decisions. The major limitation to implementing this technology often lies in the management of spatial datasets and the development of irrigation prescription maps that address variables impacting yield and soil moisture. While certain datasets and mapping technologies exist in practice, this study explored the utility of the recently developed cosmic-ray neutron probe (CRNP) which measures soil water content (SWC) in the top ~30cm of the soil profile. The key advantages of CRNP are that the sensor is passive, non-invasive, mobile and soil temperature-invariant, making data collection more compatible with existing farm operations and extending the mapping period. The objectives of this study were to: 1) improve the delineation of management zones within a field and 2) estimate spatial soil hydraulic properties (i.e. field capacity and wilting point) to make effective irrigation prescription maps. To accomplish this, a series of CRNP SWC surveys were collected in a 53-ha field near Sutherland, Nebraska. The SWC surveys were analyzed using Empirical Orthogonal Functions (EOF) to isolate the underlying spatial structure. Results indicated the measured SWC at field capacity and wilting point were better correlated to CRNP EOF as compared to other commonly used datasets. Based on this work, a soil sampling strategy and CRNP EOF analysis was proposed for better quantifying soil hydraulic properties. While the proposed strategy will increase overall effort as compared to traditional techniques, rising scrutiny for agricultural water-use may increase the adoption of this technology. Advisor: Trenton Fran