Economic and environmental concerns surrounding nitrogen (N) have motivated efforts to improve estimates of plant available N in soil in order to improve crop N management decisions. Cover crops have been recognized as an effective tool for protecting soil and enhancing soil function including N cycling. This recognition has increased the adoption of cover cropping in the United States. Despite this growing popularity, there is lack of consistent response of cover crop on soil health and only a few experiments have examined how cover crop impacts nitrogen (N) management in corn. Therefore, the objectives of this study were to: a) quantify the impacts of cover crops on various soil health indicators like permanganate oxidizable carbon (POXC), CO2 burst, autoclaved-citrate extractable (ACE)-soil protein, b) investigate the relationship between soil health indicators, soil nitrate (NO3-N) and ammonium (NH4-N), corn N requirement and corn yield, and c) study the decomposition and N release of different cover crops. In a comparison of cover crop treatments, there was a trend of increasing permanganate oxidizable carbon (POXC) and CO2 burst with cover crop compared to no-cover crop control in the short term (1 year). Additionally, CO2 burst values were significantly increased for a long-term site with cover crops compared to the control in both 2021 and 2022. A long-term cover crop study at 25 sites showed a weak relationship of CO2 burst, POXC, soil protein and NO3-N with agronomic optimum N rate (AONR), with r values ranging from 0.00 to 0.48, suggesting these indicators may not be reliable predictors of N available in soil and corn yield. However, there was significant relationship between NO3-N at N sidedress time and relative yield (r = 0.65) at these long-term sites. In short-term cover crop study (Chapter 1), Presidedress nitrate test (PSNT) nitrate concentration was >15 mg kg-1 at 5 sites and in long term cover crop study (Chapter 2), 15 sites had nitrate concentration > 15 mg kg-1 indicating potential of N sidedressing reduction when compared to current pre-sidedress N test (PSNT) N recommendation in Virginia, which is currently only recommended for sites receiving manure or biosolids. A cover crop decomposition study at Kentland showed that hairy vetch had a faster decomposition rate (k = 0.0377 g g-1 d-1) than rye and vetch mix (k = 0.0292 g g-1 d-1) or cereal rye (0.0227 g g-1 d-1) with 0 N fertilizer and released more N than cereal rye and rye and vetch mix. The difference in C: N ratio (hairy vetch (9-11:1), cereal rye (31-46:1), rye and vetch mix (19-20:1)) may have affected decomposition rate and N release of cover crops. Hairy vetch released significant amounts of N within a month of incubation, with 103 kg N ha-1 in 2021 and 57 kg N ha-1 in 2022. Overall, this study showed that cover crops did not have a consistent or significant effect on soil health indicators in short term. However, cover crops improved CO2 burst at long term cover crop site compared to no-cover, control. Future studies should focus on understanding best methods of predicting N available to subsequent crop and conduct cover crop decomposition studies across the state with different cover crop species and their mixture. / Doctor of Philosophy / Increasing food production and fertilizer application especially nitrogen has degraded the soils capacity to provide nutrient to crops. Cover crops are crops planted after harvesting main crops like corn, soybean and cotton to protect soil from erosion and improve the soil's nutrient supply capacity. Planting cover crops in fall rather than leaving soil bare can be a best management practice to improve the soils and reduce the nitrogen loss to water bodies. The purpose of this study was to measure soil properties that shows how healthy the soil is, find the relation of soil properties with corn N requirement and corn yield, and estimate decomposition rate and nitrogen release after cover crop termination. Results showed that one year of cover crop versus no-cover crop had no effect on active carbon (permanganate oxidizable carbon, POXC), microbial respiration (CO2 burst). However, long term cover cropping increased CO2 burst. In long term cover cropping fields, nitrate concentration measured before N sidedress time (also called presidedress nitrate test, PSNT) was increased at 15 sites indicating these sites could reduce their N sidedressing. Cover crop decomposition study showed that decomposition and nitrogen release from hairy vetch was faster than cereal rye, and cereal rye and vetch mixture. Overall, planting cover crop showed did not improve in short term but planting cover crop for long term have potential to reduce the amount of nitrogen fertilizer need for corn, especially when legume cover crops are use.
| Identifer | oai:union.ndltd.org:VTETD/oai:vtechworks.lib.vt.edu:10919/115274 |
| Date | 31 May 2023 |
| Creators | Pokhrel, Sapana |
| Contributors | Crop and Soil Environmental Sciences, Maguire, Rory Owen, Flessner, Michael L., Thomason, Wade Everett, Reiter, Mark S., Stewart, Ryan D. |
| Publisher | Virginia Tech |
| Source Sets | Virginia Tech Theses and Dissertation |
| Language | English |
| Detected Language | English |
| Type | Dissertation |
| Format | ETD, application/pdf, application/pdf |
| Rights | In Copyright, http://rightsstatements.org/vocab/InC/1.0/ |
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