Document Type

Dissertation - Open Access

Award Date

2021

Degree Name

Doctor of Philosophy (PhD)

Department

Agronomy, Horticulture, and Plant Science

First Advisor

Thandiwe Nleya

Abstract

Integrated crop-livestock systems (ICLs), if managed properly, have the potential for enhancing crop production and economics. Cover crops in ICL can be grazed to provide feed for livestock and improve nutrient recycling. This dissertation focused on assessing the impacts of ICL on crop yield and economics using field and modeling studies. Specific objectives of this dissertation are: (i) evaluating the impacts of the ICL on crop yield, and economic performance in a 3-yr oat (Avena sativa L.) – maize (Zea mays L.) – soybean (Glycine max (L.) Merr.) rotation, (ii) assessing the impacts of the ICL on maize biomass accumulation, harvest index (HI) and uptake of N, P, K, S, Ca, and Mg nutrients during the reproductive phase, (iii) evaluating the Cropping System Model (CSM)- CERES-Maize and CSM-CROPGRO-Soybean models for the prevalent no-till (NT) and conventional-till (CT) systems, and comparing the long-term impacts of NT and CT on crop yield and soil organic carbon (SOC), and (iv) developing a simple simulation methodology for crop-livestock interaction using Decision Support System for Agrotechnology Transfer (DSSAT), and evaluating the performance of cover crops grazing on maize production. The field study was established in 2016 and included treatments comprising of (i) oat – maize – soybean (CNT), (ii) oat – cover crops – maize – soybean (CC), and (iii) oat– cover crop + grazing – maize + residue grazing – soybean + residue grazing (ICL). The crop yield was unaffected by the cover crops or livestock grazing over the study period. A 17.7% reduction in maize yield under CC as compared to the CNT was observed for 2017, however, the differences were non-significant (P = 0.06). Despite no significant differences in crop performance, the economic analysis showed ICL to be significantly more profitable (P = 0.003) than the CNT (64 % higher returns) and CC (91% higher returns). To determine whether ICLs are better in nutrient recycling, nutrient uptake for N, P, K, S, Ca, and Mg was estimated in the above ground maize biomass at R1 and R6 growth stages, along with HI. Treatments did not impact biomass yield and HI. However, N, K, S, and Ca contents of maize plants, averaged across years and growth stages, for the CNT was similar to the ICL treatment, and significantly greater than the CC treatment. Magnesium content in maize biomass was significantly greater under ICL than CNT and CC treatments. The treatments did not have any impact on P content in the above ground biomass of maize, however, the trend of CNT > ICL > CC was still observed. Field trials that involve livestock under croplands are often expensive and laborious to maintain for longer duration. Therefore, process-based cropping system models (CSM) can play a vital role in addressing some of the issues associated with longterm research. Therefore, the DSSAT program was used to develop a simulation methodology for ICL, after calibrating and evaluating the CSM-CERES-Maize and CSM-CROPGRO-Soybean using long-term crop yield data from a 2-yr maize – soybean rotation grown under prevalent CT and NT systems. A satisfactory coefficient of determination (R2) for evaluation of CSM-CERES-Maize (R2 = 1.00) and CSMCROPGRO- Soybean (R2 = 0.65) confirmed that the trends in the field data were captured well by the simulations. For simulating crop-livestock interaction using DSSAT, the difference in pregrazing and post-grazing dry biomass of the cover crops, averaged over the grazing period was used to determine the daily biomass consumption by the livestock. The invitro dry matter digestibility (IVDMD) of the cover crops was used to determine the amount of manure that is being returned to the soil during the grazing period. The data generated from the field experiments was used to calibrate and evaluate the CSMCERES- Maize of the Decision Support System for Agrotechnology Transfer (DSSAT). The index of agreement (d) values for calibration and evaluation of maize yield were 0.99 and 0.95, respectively. The trends in the field data were, therefore, well represented by the simulated data. Results of the study suggest that livestock grazing did not incur any yield penalties on the cash crop and made the system more profitable. The nutrient recycling in above ground maize biomass, although insignificant, was improved in case of ICL as compared to cover crops without grazing. These results suggest that incorporating cover crops in ICLs can enhance nutrient recycling and improve farm profitability. The simulation methodology developed in DSSAT using field data can be applied further for various crop-livestock interactions and scenario analysis by scientists and policy-makers alike. However, extensive testing and further improvements in the methodology may be expected.

Library of Congress Subject Headings

Integrated agricultural systems.
Integrated agricultural systems -- Economic aspects.
Cropping systems.
Plant nutrients.
Crop yields.
Grazing.
Crop rotation.
Crop diversification.

Number of Pages

160

Publisher

South Dakota State University

Rights

Copyright © 2021 the Author

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