(128c) Effects of Microbial Soil Amendments to Improve Soil Water Availability and Denitrification.

This work investigates the use of Bacillus subtilis as a soil additive that can improve water retention in agricultural soils, reducing water demands during periods of drought stress. In the soil, B. subtilis can produce cyclic lipopeptides as secondary metabolites that act as surfactants, breaking down soil water repellency and generating hydrophilic soils, enhancing soil water-holding capacity. In the prior work, B. subtilis was added to sandy loam soils in a lab-scale system; here, it was found that soil inoculated with B. subtilis can decrease the soil moisture threshold, increasing soil moisture availability. In the current work, we investigate the effect that different forms of inorganic nitrogen (N) have on B. subtlis mediated soil wetting. Evaporation experiments were conducted by treating B. subtilis inoculated soils with various forms of nitrogen (NH₄NO₃, NH₄Cl, NaNO₃), representative of different nitrogen-based fertilizers. Evaporation rates and soil water retention levels were then measured while heating the soils. Results indicated that soils treated with NH₄NO₃ retained significantly more water than untreated soils and soils treated with other forms of nitrogen. Inorganic nitrogen levels (ammonium, nitrate) were quantified during each experiment using KCl extraction to show that soils treated with NH₄NO₃ undergo the most intense denitrification process, reducing nitrate levels well below initial levels, despite adding more nitrates during the inoculation. These findings indicate that soils amended with NH₄NO₃ provided the highest gains in soil water retention and that inoculating soils with B. subtilis could deliver multiple benefits to stressed agriculture soils by both increasing soil water holding capacities and by providing denitrification to reduce nitrogen runoff and loss.