Field-scale Characterization of Soil Structure and Hydraulic Properties for Variable-Rate Irrigation

Soil structure and hydraulic properties are essential indicators for soil sustainability. The importance of soil sustainability goals has been pointed out by the United Nations. Two major roles that soil scientists play in the development of sustainability indicators are “applying dynamic models” and quantifying “spatial patterns of soils”, because our existing soil maps are insufficient to support management decisions and agro-ecological models (Bouma et al., 2019). Over the past years, KYSGGA, CGA and KSB have supported our work especially in identifying spatial patterns of soils and crops at the field scale to investigate their relationships. With the present proposal, we plan to continue our efforts to obtain better soil data for water transport in soils, and to provide a soil map which is meaningful and relevant for variable-rate irrigation, landform characterization, and nutrient accessibility and losses. In our previous years’ investigations at Hillview Farms in Princeton, Caldwell County, we found that soil clay content variability measured in a 100-acre field caused differences in the ability of the soil to take up water from natural rainfall and irrigation. Soil cores had been collected at 46 locations in the surface layer (3-5” depth). At this point, we lack information of soil hydraulic conductivity measured directly in the field at the surface layer as well as in deeper soil layers. Knowing hydraulic behavior for different soil layers would help us to support variable rate irrigation decisions and provide the quantitative information that we need for predicting water availability in different zones of the field. For this purpose, we will conduct borehole infiltration measurements at 42 locations each at 3, 12, 24, and 36” depth to obtain a data set for different soil horizons in the profile. For these locations, we already have comprehensive soil textural profile information. We will use three existing borehole infiltrometers for these measurements. The data will be analyzed spatially, and their spatial relationship to soil clay content, crop growth and yield and VERIS electrical conductivity (EC) will be quantified. We are also interested in the relationships of water permeability at different soil depths with each other. To what extent is the spatial pattern of hydraulic conductivity measured at the land surface related to that in deeper layers? The outcome will be better site-specific water and nutrient management and a functional soil map. The total costs for this project (student workers for field measurements; travel to the experimental site and overnight-stay; replacement parts for infiltrometers; soil augers) are estimated with $7,000.