Author ORCID Identifier

https://orcid.org/0000-0003-4180-7081

Date Available

4-29-2021

Year of Publication

2021

Document Type

Master's Thesis

Degree Name

Master of Science (MS)

College

Agriculture, Food and Environment

Department/School/Program

Plant and Soil Sciences

Advisor

Dr. Hanna J. Poffenbarger

Abstract

In Central Kentucky, rolling hill cropland presents a number of challenges related to soil sustainability. Increased topographic complexity can lead to increased erosion, inefficient crop nutrient use and increased nutrient loss. Further, grain crop yields can be variable across both space and time in rolling hill fields and are less resilient to changes in weather conditions than flatter, more homogeneous areas. More than 30% of cropland in Kentucky has a slope greater than 3⁰, which means a large swath of the row crop production land in the state is at increased risk of contribution to soil and water resource degradation. Managing these croplands in a way that secures the economic and environmental sustainability of Kentucky producers is critical to ensuring food system security on a local scale, and increase the viability of Kentucky ecosystems, both managed and natural.

Cover crops, crops grown for ecosystem benefits rather than harvested for profit, may be a way of reducing the impact of complex topography on row crop production. Cover crops have been shown to reduce erosion losses, prevent nutrient loss to groundwater, and improve soil quality. Further when grown in a mixture, such as a cereal-legume biculture, cover crops have been shown to exhibit multifunctional traits, such as coupling N retention and release in synchrony with crop uptake. As such, they may present a management practice that can increase the sustainability of rolling hill agroecosystems, and possibly reduce the spatial and temporal variability in yield and biogeochemical cycling. There has been some research on the interaction between topography and cover crop implementation conducted up to this point. Across these studies however, to the author’s knowledge, there has not been a systems level analysis of the landscape position effect on cover crop growth and dynamics, decomposition, and the subsequent interactive effect of cover crop and topography on maize development and yield. Closing this knowledge gap provides an opportunity to increase our understanding of agroecosystem processes beyond individual crop growing seasons and determine how management of winter cover crops can be improved to enhance overall agronomic outcomes.

Understanding how landscape topography impacts cover crop production, and in turn affects maize production, is critical to improving management of cover crops in Central Kentucky, and thus increasing agroecosystem sustainability. Here, we present the results of four experiments, which had the objectives of: 1.) Determining the effect of landscape position on cover crop biomass production and function, including species diversity and nitrogen fixation, 2.) Quantifying the effect of landscape position on the decomposition and N release rate of different cover crop treatments, 3.) Examining the scientific literature to determine how weather influences the relationship between grain production and topography, and 4.) Using field observations to calibrate a soil-crop system model for predictions of cover crop by topography interactions on maize yield and spatiotemporal yield stability under different climate scenarios.

Our results, detailed in the subsequent chapters, indicate that cover crop growth and function respond strongly to topographic factors such as slope, and edaphic factors such as soil texture and inorganic nitrogen. Additionally, landscape position has a significant effect on the spatial distribution of soil water, and the surface soil temperature throughout the maize growing season, but this does not translate to spatial differences in the rate of cover crop decomposition. Our analysis of the relationships between topography and crop yield indicate that maize yield varies in its response to topographic factors based on growing season precipitation, such that at low precipitation, sloping areas yield poorly, but increase in yield as growing season precipitation increases. When we expanded our field data results to different climate scenarios using a soil-crop system model, we found that the presence of cover crop residue can decrease maize yield variability across time and space by raising yields in sloping positions via increased soil water storage, especially under dry conditions. The results presented here offer further evidence that the integration of cover crops into areas of sloping topography offer outsized benefits compared to areas of homogeneous terrain, including more stable yields, and increased N return. This work provides a means for maximizing the benefits of cover crop functionality for producers and increasing the overall sustainability of Kentucky agroecosystems.

Digital Object Identifier (DOI)

https://doi.org/10.13023/etd.2021.057

Funding Information

This work was supported by the University of Kentucky College of Agriculture Food and the Environment, the University of Kentucky Department of Plant and Soil Sciences, the Southern Sustainable Agriculture Research and Education Graduate Student Grant [GS19-231] (2019), the United States Department of Agriculture National Institute of Food and Agriculture Grant Number [2020-67013-30860] (2020), the Kentucky Corn Growers Association (2020), and the Karri Casner Environmental Sciences Fellowship (2019).

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