Soil Moisture Retention on the High Plains of North America via Compost Amendments: A Longitudinal Field Study

Abstract

Water is a finite but vital resource, and the volume of water used in arid and semi-arid regions must be managed to its fullest and best use. Irrigation water is approximately 37% of the total water used in the United States by volume annually. Thus, this area of water use is critical for local and national water conservation. Irrigation is primarily used to increase soil water content above that which precipitation can supply. Soil structure and associated effects on drainage and evapotranspiration, however, largely control soil water content, no matter the amount of applied water. Therefore, improving soil structure to hold more water decreases the amount of water needed for irrigation, which frees that water for other uses. In this paper, organic compost amendments are studied to determine the change in soil structure and accompanying improvements in soil water content over a 4-year period. A uniform field site was selected for this research in the high plains of South Dakota, where irrigation water was available for crop growth. The test site was divided into two equal area fields; one without compost and a field with compost amendments added to 20 cm depth. Compost was incorporated into the treated field at rates of 5% and 10% by weight. Both fields received the same tillage, seed, fertilizer, weather and irrigation. Weekly to monthly in-situ water content measurements from both fields were recorded at the surface and the depths of 20, 40 and 60 cm from 2017 to 2020. Precipitation and applied irrigation water were recorded at the site. No irrigation occurred in 2019 and 2020, and moisture content was dependent on natural precipitation in those years. Results of water content and soil structure show significant differences in the water contents of the soils with the compost amendments compared to baseline, with higher compost content resulting in higher water contents without the soil becoming over-saturated. These results were consistent at all depths and across all growing seasons. This work demonstrates the efficacy of compost soil amendments in regulating soil moisture, which has profound impacts on crop yields, topsoil erosion losses, carbon sequestration, and water conservation.