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Title:Legacy effects of cover crop monocultures and mixtures on soil inorganic nitrogen, total phenolic content, and microbial communities on two organic farms in Illinois
Author(s):Lucadamo, Eleanor Elizabeth Kirk
Advisor(s):Yannarell, Anthony C.
Department / Program:Natural Res & Env Sci
Discipline:Natural Res & Env Sciences
Degree Granting Institution:University of Illinois at Urbana-Champaign
Subject(s):cover crops
inorganic nitrogen
potentially mineralizable nitrogen
phenolic content
soil microbial communities
soil microbial diversity
partial least squares regression
Abstract:Cover crops can leave behind legacy effects on their soil environments by influencing soil inorganic nitrogen (N) pools, total phenolic content through the release of secondary compounds, and by altering soil microbial communities. I analyzed soils collected during a two-year field study and aimed to determine how spring-sown cover crops (grass, legume, or Brassica monocultures or diverse, five-way mixtures) influence these three aspects of the soil environment. Soils were collected in the spring of 2015 and 2016 on two different organic farms in Central and Northern Illinois, PrairiErth and Kinnikinnick, during the four weeks post-cover crop incorporation. The first part of this study addressed the influence of cover crops on soil inorganic N (nitrate, ammonium, and potentially mineralizable N, PMN) and total phenolic content intensity, as measured by the integrated area under the curve of the three sample dates plotted against time. I found that Brassica monocultures, the most productive cover crop treatment, resulted in the lowest soil nitrate intensities and greatest soil PMN intensities, but they did not affect the total phenolic content of the soil. Weedy contributions to total plant biomass were also important in determining soil inorganic nitrogen levels, and weed biomass was positively correlated with soil PMN intensity. The second part of this study addressed the changes in microbial community structure and -diversity as a result of cover crop type as well as identified specific cover crop drivers that were associated with individual microbial taxa using partial least squares regression (PLSR) modeling. I found the greatest bacterial -diversity under Brassicas and the lowest under the plant-free control plots. Fungal diversity, in contrast, was greatest under the plant-free control plots and lowest in the Brassica monocultures. Idagold mustard, weeds, and oat were the most influential cover crops in describing bacterial and fungal taxa according to the PLSR models. Though taxa often displayed individualistic responses, I found that Idagold mustard biomass was positively associated with several pathogen-suppressive taxa and negatively associated with pathogenic taxa. Ammonia-oxidizing archaea were abundant among the top model results and appeared to be suppressed by Idagold mustard and oat at both farms. In conclusion, Brassicas were the most effective at reducing soil nitrate and increasing PMN concentrations, which reduces risks of nitrate leaching after cover crop termination and increases the potential inorganic N supply for subsequent crops. Brassicas also increased bacterial diversity and decreased fungal diversity, which could have implications for managing subsequent crop disease. Landowners should consider their cover crop goals (reducing soil nitrate leaching, increasing inorganic N for subsequent crops, or mitigating crop disease) when evaluating cover crop type and diversity.
Issue Date:2018-07-12
Rights Information:Copyright 2018 Eleanor Lucadamo
Date Available in IDEALS:2018-09-27
Date Deposited:2018-08

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