Document Type

Dissertation - Open Access

Award Date

2020

Degree Name

Doctor of Philosophy (PhD)

Department / School

Agronomy, Horticulture, and Plant Science

First Advisor

Sandeep Kumar

Keywords

grazing cover crops, greenhouse gas emissions, HYDRUS model, integrated crop-livestock system, soil physical and hydrological properties, X ray computed tomography

Abstract

Cover crops (CCs) and grazing play a critical role in successful implementation of the integrated crop-livestock system (ICLS) because they can have a direct impact on soils and greenhouse gas emissions. The objectives of this study were to (i) evaluate the short-term impacts of CCs [grass dominated cover crops (GdC) and legume dominated cover crops (LdC)] and grazed CCs and corn (Zea mays L.) residue under oat (Avena sativa L.)–CC–corn rotation on soil physical and hydrological properties; (ii) quantify the architecture of soil pores using X-ray computed tomography (CT) for soils managed under long-term ICLS, native grazed pasture and corn-soybean cropping system, and to examine relationships between CT-measured pore parameters and soil hydro-physical properties; (iii) evaluate the impact of CCs (GdC and LdC) and grazed CCs and corn residue under oats-CCs-corn rotation on soil surface carbon dioxide (CO2), nitrous oxide (N2O) and methane (CH4) fluxes; and (iv) simulate water content and temperature for soils using HYDRUS model under grass dominated CC, cattle grazedgrass dominated CC and bare soils under ICLS. Cover crops reduced soil bulk density (b) and soil penetration resistance (SPR) at 0-10 and 10-20 cm depths and, in general, increased soil water retention (SWR) and total porosity compared to the no cover crops. Cattle grazing generally increased the b and SPR at both depths, however, the values of SPR did not surpass the critical values which indicated that the grazing did not have an adverse effect on soils in terms of root proliferation. Retention of water and total pore space in soil was reduced due to the grazing. Long-term ICLS enhanced CT-measured macroporosity (0.084 mm3 mm-3) and reduced b (1.18 Mg m-3) compared to the corn-soybean cropping system (0.012 mm3 mm-3; 1.51 Mg m-3). The increased proportion of pore volume contained in the largest pore cluster and higher connected porosity under long-term ICLS significantly enhanced saturated hydraulic conductivity (Ksat) of the soils compared to the corn-soybean cropping system. The GdC+G appeared to reduce cumulative CO2 (4042 kg C ha-1) and N2O (1499 g N ha-1) fluxes compared to the LdC+G (4819 kg C ha-1for CO2 and 2017 g N ha-1 for N2O), indicating the superiority of GdC+G over the LdC+G in reducing the greenhouse gas (GHG) fluxes in short-term. Cumulative CH4 flux was not affected by ICLS. The HYDRUS model was used to simulate soil water content and soil temperature from the GdC, GdC+G and no cover crop and G (NC) treatments. The model was calibrated using data from 2017 and then validated with data from 2018 growing season. The R2 and index of agreement (d) values for simulations of soil water content varied from 0.26–0.78 and 0.52–0.89, respectively during the validation period. The corresponding values for soil temperature were 0.48–0.99 and 0.80–0.99, respectively. The model performed better in simulating soil temperature compared to that of the soil water content over the study period. This study illustrates that cover cropping in shorter duration (2-3 yr) enhanced some soil physical attributes, however, grazing cover crops and crop residue had small or neutral effects on soils. The CT-study represented the benefits of long-term ICLS for maintaining or improving soil pore connectivity and other parameters critical for soil water transport. The GHG study showed that, in general, cover crops and grazing of cover crop and corn residue did not impact CO2, N2O and CH4 fluxes in short-term. Long-term studies are required to capture the influence of management practices such as ICLS on GHG fluxes. The modeling study showed that owing to the satisfactory performance of HYDRUS in simulating soil water content and temperature under ICLS, and this model can act as a promising tool in simulating the long-term benefits of conservation practices that involve diverse CCs and grazing CCs and crop residue in enhancing the soil moisture conservation. Overall, the results of this study indicate that integrating livestock grazing in the row crop rotations that involve diverse CCs can improve soil physical and hydrological properties and has a potential to mitigate greenhouse gas emissions.

Library of Congress Subject Headings

Integrated agricultural systems -- Environmental aspects.
Greenhouse gases.
Cropping systems.
Crops and soils.
Grazing.
Cover crops.

Format

application/pdf

Number of Pages

256

Publisher

South Dakota State University

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Rights Statement

In Copyright