{"id":{"repo_id":"uiuc","oai_identifier":"oai:www.ideals.illinois.edu:2142/116145"},"canonical_url":"https://search.dev.ndltd.org/etd/uiuc/oai:www.ideals.illinois.edu:2142/116145","repository":{"repo_id":"uiuc","name":"University of Illinois - Urbana-Champaign","base_url":"https://www.ideals.illinois.edu/oai-pmh"},"display":{"title":"Soil microbial aspects of cover cropping as conservation practice for corn monocultures under heavy nitrogen fertilization","abstract":"Submission original under an indefinite embargo labeled 'Open Access'. The submission was exported from vireo on 2022-11-15 without embargo terms","abstract_html":"Submission original under an indefinite embargo labeled 'Open Access'. The submission was exported from vireo on 2022-11-15 without embargo terms","abstract_has_math":false,"creators":["Kim, Nakian (Nak Hyun)"],"institution":"University of Illinois at Urbana-Champaign","degree_name":"Ph.D.","degree_level":"Dissertation","degree_discipline":"Crop Sciences","degree_department":null,"school":null,"contributors":["Villamil, María B","Riggins, Chance W","Rodriguez-Zas, Sandra L","Zabaloy, María C"],"advisors":[],"committee_chairs":[],"committee_members":[],"year":2022,"date_issued":"2022-08","date_published":"2022-08","updated_at":"2026-07-22T22:24:55Z","subjects":["Cover cropping","N fertilization","Mollisols","sustainable agriculture","microbiology","soil biodiversity"],"languages":["en","eng"],"rights":["Copyright 2022 Nakian (Nak Hyun) Kim"],"rights_urls":[],"identifier_entries":[]},"links":{"outbound_url":"https://hdl.handle.net/2142/116145","outbound_label":"Handle","outbound_source":"dc:identifier"},"metadata_groups":[{"id":"people","label":"People","entries":[{"key":"dc:contributor","label":"Contributor","values":["Villamil, María B","Riggins, Chance W","Rodriguez-Zas, Sandra L","Zabaloy, María C"]},{"key":"dc:creator","label":"Author","values":["Kim, Nakian (Nak Hyun)"]}]},{"id":"academic_context","label":"Academic Context","entries":[{"key":"dc:date","label":"Dc Date","values":["2022-08","2022-05-31"]},{"key":"dc:type","label":"Dc Type","values":["text","Thesis"]},{"key":"thesis:degree_discipline","label":"Discipline","values":["Crop Sciences"]},{"key":"thesis:degree_level","label":"Degree Level","values":["Dissertation"]},{"key":"thesis:degree_name","label":"Degree Name","values":["Ph.D."]},{"key":"thesis:institution_name","label":"Thesis Institution Name","values":["University of Illinois at Urbana-Champaign"]}]},{"id":"subjects_keywords","label":"Subjects and Keywords","entries":[{"key":"dc:subject","label":"Dc Subject","values":["Cover cropping","N fertilization","Mollisols","sustainable agriculture","microbiology","soil biodiversity"]}]},{"id":"language_rights","label":"Language and Rights","entries":[{"key":"dc:language","label":"Dc Language","values":["en","eng"]},{"key":"dc:rights","label":"Dc Rights","values":["Copyright 2022 Nakian (Nak Hyun) Kim"]}]},{"id":"identifiers","label":"Identifiers","entries":[{"key":"dc:identifier","label":"Identifier","values":["https://hdl.handle.net/2142/116145"]}]},{"id":"additional","label":"Additional Metadata","entries":[{"key":"dc:description","label":"Description","values":["Submission original under an indefinite embargo labeled 'Open Access'. The submission was exported from vireo on 2022-11-15 without embargo terms","The student, Nakian (Nak Hyun) Kim, accepted the attached license on 2022-05-17 at 21:18.","The student, Nakian (Nak Hyun) Kim, submitted this Dissertation for approval on 2022-05-17 at 22:06.","This Dissertation was approved for publication on 2022-05-31 at 15:30.","DSpace SAF Submission Ingestion Package generated from Vireo submission #18033 on 2022-11-15 at 17:37:27","Soil health degradation and nutrient losses are major symptoms of chemical imbalances from excessive nitrogen (N) fertilization in the crucial agricultural regions of the world. Cover cropping (CC) is a promising conservation practice with potentials to mitigate these detriments and improve soil health. Despite the fundamental roles that the soil microbial community plays as drivers of soil processes, how it responds to CC has not been well documented for the intensely managed simplified cropping systems. Thus, the aim of this research was to investigate whether introducing CC to a simplified cropping system can mitigate the disruption of its soil microbial community by heavy N fertilization. For this, the objectives of this research were to i) obtain baseline data by characterizing the soil before introducing CC, ii) describe this system’s soil microbial community after introducing CC, using bioindicators of high taxonomic resolution, and iii) characterize the soil N-cycling microbial community using its functional genes and nitrification and denitrification functionalities with enzyme assays. The baseline soil characterization was done to a depth of 90 cm in corn [Zea mays L.] monoculture (CCC) and the corn (Cs) and soybean [Glycine max (L.) Merr.] (Sc) phases of a corn-soybean (CS) rotation that received inorganic N fertilizers at successive rates (N0, N202, N269; kg N ha-1) for 36 years. The experimental plots were arranged as a split-plot in a randomized complete block design with three replicates. The characterizations of the soil microbial communities were done on the corn monoculture plots of this site with subplots of CC mixture of cereal rye [Secale cereale L.] and hairy vetch [Vicia villosa Roth.] (CC), and winter fallow controls (BF). The N rates and CC treatments plots were studied as a 3x2 split-plot arrangement in a randomized complete block design with three replicates for two years. The baseline soil characterization before CC observed that N fertilization within CCC significantly acidified the topsoil from pH 6.6 (N0) to pH 4.9 (N269), while increasing the nitrate (NO3-) level up to eight-fold. Within CCC, available phosphorus level was more than twice higher, and potassium was 40% higher with N0 than fertilized soils. Sc had lower water aggregate stability (WAS) than CCC and bulk density (Bd) decreased by 5% from N0 to N269 across rotations. After introducing CC, soil NO3- decreased by up to 50% across N rates, and CC biomass increased by 73% with N fertilization. The characterization of the soil microbial community found that N fertilizers increased the abundances acidophiles, NO3- reducers, and NO2- oxidizers, while various N-cycling genera including heterotrophic nitrifiers, nitrite oxidizers, and complete denitrifiers increased with N0. CC promoted eight indicators of diverse functions and niches, while only two N-cycling genera associated with BF. Finally, N fertilization decreased the abundances of nifH, archaeal amoA, and nirS by 7.9, 4.8, and 38.9 times, respectively, and they correlated positively with soil pH. CC increased the abundances of nirK by 1.5 times when fertilized. Bacterial amoA increased by 2.4 times with CC within N269, while N202 and N269 did not differ from N0 within BF; it also correlated positively with soil nitrate. Overall, this research found that CC could enhance the soil biodiversity of this system and reduce NO3- leaching but also increase the risks of nitrous oxide emissions without proper nutrient management. It also identified soil acidification and high N availability as the primary factors by which excessive N fertilization disrupts the soil microbial community. However, CC might not be enough to mitigate this process for N-cycling communities that have become resistant to conservation practices after long-term adaption to disruptions. This research provided valuable references for future CC research on these systems and its results can serve as primary information to understand the potentials and limitation of CC as a conservation practice."]},{"key":"dc:format","label":"Dc Format","values":["application/pdf"]},{"key":"dc:title","label":"Title","values":["Soil microbial aspects of cover cropping as conservation practice for corn monocultures under heavy nitrogen fertilization"]}]}],"canonical_facts":{"dc:contributor":["Villamil, María B","Riggins, Chance W","Rodriguez-Zas, Sandra L","Zabaloy, María C"],"dc:creator":["Kim, Nakian (Nak Hyun)"],"dc:date":["2022-08","2022-05-31"],"dc:description":["Submission original under an indefinite embargo labeled 'Open Access'. The submission was exported from vireo on 2022-11-15 without embargo terms","The student, Nakian (Nak Hyun) Kim, accepted the attached license on 2022-05-17 at 21:18.","The student, Nakian (Nak Hyun) Kim, submitted this Dissertation for approval on 2022-05-17 at 22:06.","This Dissertation was approved for publication on 2022-05-31 at 15:30.","DSpace SAF Submission Ingestion Package generated from Vireo submission #18033 on 2022-11-15 at 17:37:27","Soil health degradation and nutrient losses are major symptoms of chemical imbalances from excessive nitrogen (N) fertilization in the crucial agricultural regions of the world. Cover cropping (CC) is a promising conservation practice with potentials to mitigate these detriments and improve soil health. Despite the fundamental roles that the soil microbial community plays as drivers of soil processes, how it responds to CC has not been well documented for the intensely managed simplified cropping systems. Thus, the aim of this research was to investigate whether introducing CC to a simplified cropping system can mitigate the disruption of its soil microbial community by heavy N fertilization. For this, the objectives of this research were to i) obtain baseline data by characterizing the soil before introducing CC, ii) describe this system’s soil microbial community after introducing CC, using bioindicators of high taxonomic resolution, and iii) characterize the soil N-cycling microbial community using its functional genes and nitrification and denitrification functionalities with enzyme assays. The baseline soil characterization was done to a depth of 90 cm in corn [Zea mays L.] monoculture (CCC) and the corn (Cs) and soybean [Glycine max (L.) Merr.] (Sc) phases of a corn-soybean (CS) rotation that received inorganic N fertilizers at successive rates (N0, N202, N269; kg N ha-1) for 36 years. The experimental plots were arranged as a split-plot in a randomized complete block design with three replicates. The characterizations of the soil microbial communities were done on the corn monoculture plots of this site with subplots of CC mixture of cereal rye [Secale cereale L.] and hairy vetch [Vicia villosa Roth.] (CC), and winter fallow controls (BF). The N rates and CC treatments plots were studied as a 3x2 split-plot arrangement in a randomized complete block design with three replicates for two years. The baseline soil characterization before CC observed that N fertilization within CCC significantly acidified the topsoil from pH 6.6 (N0) to pH 4.9 (N269), while increasing the nitrate (NO3-) level up to eight-fold. Within CCC, available phosphorus level was more than twice higher, and potassium was 40% higher with N0 than fertilized soils. Sc had lower water aggregate stability (WAS) than CCC and bulk density (Bd) decreased by 5% from N0 to N269 across rotations. After introducing CC, soil NO3- decreased by up to 50% across N rates, and CC biomass increased by 73% with N fertilization. The characterization of the soil microbial community found that N fertilizers increased the abundances acidophiles, NO3- reducers, and NO2- oxidizers, while various N-cycling genera including heterotrophic nitrifiers, nitrite oxidizers, and complete denitrifiers increased with N0. CC promoted eight indicators of diverse functions and niches, while only two N-cycling genera associated with BF. Finally, N fertilization decreased the abundances of nifH, archaeal amoA, and nirS by 7.9, 4.8, and 38.9 times, respectively, and they correlated positively with soil pH. CC increased the abundances of nirK by 1.5 times when fertilized. Bacterial amoA increased by 2.4 times with CC within N269, while N202 and N269 did not differ from N0 within BF; it also correlated positively with soil nitrate. Overall, this research found that CC could enhance the soil biodiversity of this system and reduce NO3- leaching but also increase the risks of nitrous oxide emissions without proper nutrient management. It also identified soil acidification and high N availability as the primary factors by which excessive N fertilization disrupts the soil microbial community. However, CC might not be enough to mitigate this process for N-cycling communities that have become resistant to conservation practices after long-term adaption to disruptions. This research provided valuable references for future CC research on these systems and its results can serve as primary information to understand the potentials and limitation of CC as a conservation practice."],"dc:format":["application/pdf"],"dc:identifier":["https://hdl.handle.net/2142/116145"],"dc:language":["en","eng"],"dc:rights":["Copyright 2022 Nakian (Nak Hyun) Kim"],"dc:subject":["Cover cropping","N fertilization","Mollisols","sustainable agriculture","microbiology","soil biodiversity"],"dc:title":["Soil microbial aspects of cover cropping as conservation practice for corn monocultures under heavy nitrogen fertilization"],"dc:type":["text","Thesis"],"thesis:degree_discipline":["Crop Sciences"],"thesis:degree_level":["Dissertation"],"thesis:degree_name":["Ph.D."],"thesis:institution_name":["University of Illinois at Urbana-Champaign"]},"updated_at":"2026-07-22T22:24:55Z"}