A novel soil amendment for enhancing soil moisture retention and soil carbon in drough-prone soils

Crop yield reductions are common in drought stressed agroecosystem and are likely to increase with climate change and continued unsustainable rates of aquifer drawdown. To combat this, soil amendments are often used to improve soil moisture retention. However, many available amendments do not necessarily have the specific properties that could synergistically influence the complex combination of mechanisms related to soil water retention. Moreover, even as concerns over agricultural water use mount, we continue to waste a large fraction of the food we produce. In an effort to divert more food production byproducts back to agricultural fields while concurrently ameliorating drought-prone soils, we evaluated lactobionate, a major dairy industry byproduct, as a potential soil amendment for enhancing both soil moisture and SOC. Lactobionate, inherently hydrophilic and consisting primarily of cations and sugar molecules, could synergistically modify numerous controls on soil-water balances. In a laboratory setting, we compared lactobionate (LB) stabilized with various cations (K+, NH4+, and Ca+) across a range of soil types to determine LB effects on soil moisture and SOC retention compared to unamended soils. All the lactobionate amendments increased soil water content relative to unamended soil across a range of soil matric potentials and raised available water content by 37%. Water content was initially related to SOC but by two months elevated soil moisture in LB-amended soil was independent of SOC. Additionally, LB amended soils had an average 70 times higher microbial biomass and decreased soil inorganic nitrogen content compared to unamended soils. We found that K-LB, the most consistently effective of the amendments, increased soil water content by 1-6 times compared to unamended soils and total SOC was still double the native SOC at the end of the two-month incubation. Our results suggest that tapping into novel sources of organic inputs such as lactobionate may be an effective approach for simultaneously enhancing soil water retention and soil C stocks while increasing the economic and energetic value of food production byproducts.