Evaluating the impacts of biodegradable sprayable mulch and climate-adaptive management on soybean productivity: a multi-scale study

Abstract

The past few decades have witnessed unprecedented global climate change, characterized by rising temperatures and changing precipitation patterns. These trends are projected to intensify in the future. Warming accelerates crop phenological development and shortens the reproductive period, which is critical to grain yield, while rising temperatures increase soil water evaporation and crop water stress, affecting both rainfed and irrigated systems. Addressing these risks requires both fine-resolution assessments of projected climate impacts and the evaluation of practical in situ adaptation strategies that producers can readily implement. This dissertation presents two broad categories of adaptation strategies. The first is agronomic management, through climate-informed planting dates and the CO₂ fertilization effect on C3 crops like soybeans. The second is soil-water conservation through sprayable biodegradable mulches, a state-of-the-art alternative to conventional plastic films that reduces the labor, disposal, and microplastic pollution burdens that have long confined mulching to specialty crops. Realizing the potential of either adaptation strategy for large-scale adoption requires modeling tools that can represent them at regional scales. The overall aim of this dissertation is to assess the impacts of climate change on soybeans in southeastern Nebraska using CMIP6 climate projections and to explore adaptation and management strategies to mitigate the resulting yield and water-use penalties. A process-based point-scale crop model, DSSAT, was upscaled to the grid scale for these assessments. The specific research objectives are: (1) evaluating adaptive planting dates and elevated CO₂ impacts on soybean yields under future climate scenarios; (2) investigating water dynamics under a novel biodegradable sprayable mulch – BioWRAP; and (3) Assessing the impacts of biodegradable sprayable mulch on rainfed and irrigated soybean production systems using a process-based crop model. The DSSAT CROPGRO-Soybean model was programmed at a gridded scale to evaluate how a spring-freeze probability-based early planting date strategy and elevated atmospheric CO₂ levels could mitigate the impacts of projected climate change on soybeans. The simulations incorporated projected climate data from six General Circulation Models (GCMs) under two warming scenarios, SSP2-4.5 and SSP5-8.5. Spring freeze probabilities were studied to derive location- and year-specific “adaptive planting dates”. Results indicated that elevated CO₂ significantly improved yield over the simulation period (2026–2100). However, the effectiveness of planting dates in mitigating the impact of climate change was statistically significant only at higher warming levels. When combined, the adaptive planting strategy and CO₂ fertilization improved yield by up to 79% relative to a fixed-planting date and fixed-CO₂ scenario, although yields remained below baseline levels. These findings highlight the potential to adjust planting schedules and leverage CO₂ fertilization to help offset climate-induced yield losses. However, these strategies alone cannot fully offset climate change-driven yield declines. Therefore, additional measures, such as using longer-maturity group cultivars or breeding for thermally resilient varieties, may be necessary to sustain rainfed soybean production in the face of climate change. The second objective assessed a novel keratin-based (chicken-feather-derived) sprayable mulch, BioWRAP, and investigated three modeling frameworks to simulate its impact on soil water evaporation and pressure head dynamics. Soil column experiments were conducted to monitor soil water evaporation and pressure head changes under BioWRAP compared with bare soil. The observations revealed that cumulative evaporation under BioWRAP was up to 46% lower as compared to bare soil conditions. The modeling approaches investigated in this study included representing BioWRAP as an Equivalent Soil Layer in the HYDRUS-1D vadose zone model, and a modified Lehmann evaporation-efficiency model that introduces a potential-evaporation reduction factor, coupled with a finite-difference solution of Richards' equation (CoupLR). Both reproduced observed pressure head and cumulative evaporation with high accuracy. While a water-vapor-permeance approach based on ASTM E96 measurements of water vapor transmission rate substantially underpredicted evaporation. The modified Lehmann model developed in this work offers transferability to process-based crop models for representing sprayable mulches. Subsequently, the evaporation-efficiency method was embedded in the DSSAT source code and used to evaluate BioWRAP as a management practice for soybean under rainfed and irrigated conditions across observed (2005–2020) and projected climate conditions under SSP2-4.5 and SSP5-8.5 scenarios. Under rainfed conditions, BioWRAP produced a modest but consistent yield gain (~6%), along with improved rainfall productivity and transpiration, though yields still fell below baseline under higher warming in the far-future. Under irrigated conditions, soybean yields with-BioWRAP were not significantly different from without-BioWRAP treatment. However, BioWRAP reduced irrigation demand by roughly one irrigation event per season, indicating meaningful water savings. Collectively, these results show that a sprayable, biodegradable mulch can shift the soybean water balance toward greater conservation and productivity. Scaled across a major production region, this translates into real potential for water savings and reduced pressure on underlying aquifers. More broadly, this study demonstrates that biodegradable, sprayable mulching, long confined to smaller-scale specialty systems, merits serious consideration for large-scale grain production, and that its performance under a changing climate can be anticipated using process-based simulation models.