Determining the effects of cover crop residue on soil moisture dynamics in no-till fields using modeling and experimental approaches

Abstract

Cover crops conserve soil moisture by reducing evaporation during dry periods and runoff during heavy precipitation, as well as increasing soil water holding capacity in the long term. However, the immediate impact of cover crop residue presence and quantity on soil water content response to precipitation (infiltration) is inconsistent. In this project, the relationships among cover crop mulch characteristics and infiltration were examined through the lenses of a multi-state on-farm research trial, evaluation of a mechanistic crop-soil-water-mulch model, and a local field experiment on cover crop termination methods. In Chapter 1, soil water content data collected over 6 years in 16 states through an extensive on-farm research trial was paired with meteorological records to assess individual infiltration events occurring before cash crop canopy closure. Mean infiltration did not differ between the No Cover and Cover Crop plots, and cover crop biomass at termination (0-11,000 kg ha-1) was only occasionally a significant predictor of infiltration. In Chapter 2, soil water content data collected through the same on-farm experiment throughout the cash crop growing season (May-September) was compared to outputs from a mechanistic model, 2DMAIZSIM. The model consistently overpredicted the initial volumetric water content (VWC) and underpredicted infiltration. Integrating the impact of cover crop water use while growing and the preferential water channels formed by cover crop roots into the model structure would likely improve 2DMAIZSIM performance. Chapters 3 and 4 examine the impact of cover crop termination method on cover crop residue in a field experiment in which cereal rye (Secale cereale L.) was either roller-crimped or left standing and then sprayed with either a systemic (glyphosate) or contact (paraquat) herbicide. Cumulative infiltration and evapotranspiration from cover crop plots, as well as residue decomposition, did not differ between herbicides. Between the mechanical treatments, greater soil temperature fluctuations were observed in the roller-crimped cereal rye, as well as higher concentrations of recalcitrant chemical components (lignin and holocellulose). This body of work helps to elucidate the complex relationships between soil moisture dynamics and cover crop residue, which in turn improves guidance for growers seeking to maximize the benefits of cover crops.