Degree

Doctor of Philosophy (PhD)

Department

The School of Plant, Environmental, and Soil Sciences

Document Type

Dissertation

Abstract

The reliance on conventional cropping has profoundly impacted agricultural sustainability and resulted in soil degradation. Winter cover crops can preserve the soil surface, recycle soil nutrients, and improve soil health. Hence, the role of cover crops in Louisiana row-crop production was examined in small-scale plots and large-scale on-farm studies at three sites in Northeast Louisiana from 2017 to 2020. Additionally, mixed cover crops degradation and nutrient release were evaluated at Macon Ridge and Dean Lee sites to determine the optimum time of nutrient availability after cover crop termination. The small-scale results showed that integrating cover crops for corn (Zea Mays) production could reduce the nitrogen (N) fertilizer requirement. Legume cover crops maximized corn production at 90 kg N ha-1, while grass & brassica optimized corn grain yield at 179 kg N ha-1. Nitrogen fertilizer addition boosted soil organic matter by 8% relative to fallow treatment regardless of cover crop types. The soil extractable phosphorous (P) concentration was greater under legumes compared to grass & brassicas, while the grass & brassica had a higher soil extractable potassium (K) level than legume. Cover crops and N fertilizer added improved soil health, including soil enzymes for C and N cycling. Total microbial abundance was higher at 90 to 179 kg N ha-1 in spring among different N treatments. Arbuscular mycorrhizal fungi were increased in grass & brassica treatment compared to legume covers. The cover crops mixtures produced more biomass and assimilated more N than fallow treatments. The polyculture cover crop mixes tended to have more biomass and N produced. Two months after termination, degradation of biomass contributed to cycling nutrients to the soil. The optimum timing of inorganic N availability to cash crop was 6 weeks after cover crop termination. On-farm demonstrations showed that mixed cover crops significantly increased soil organic matter in site 1. At site 2, soil β-glucosidase and soil protein-N concentrations under mixed cover crops were higher than the fallow. However, no difference between treatments was observed in site 3 soil, likely due to site-specific differences. Soil enzymes, protein-N, and active C all increased over time in all cover-cropped fields.

Committee Chair

Lisa Fultz

Available for download on Tuesday, March 15, 2022

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