Document Type

Thesis - Open Access

Award Date

2017

Degree Name

Master of Science (MS)

Department / School

Agronomy, Horticulture, and Plant Science

First Advisor

Sandeep Kumar

Abstract

Grazing and cover crops (CC) can impact soil nutrient cycling but may increase the greenhouse gas (GHG) emissions from soils. However, little is known about their impacts on soil properties and soil surface GHG emissions in an integrated crop-livestock system (ICLS) in South Dakota, USA. The present study was conducted at a farm scale at the Research Farm of South Dakota State University, Brookings, South Dakota, to assess the impact of cover crops and grazing on soil pH, electrical conductivity (EC), and bulk density (BD), and soil surface carbon dioxide (CO2), methane (CH4), and nitrous oxide (N2O) fluxes. Study treatments included grass dominated mixture CC and broadleaf dominated mixture CC, both with and without grazing, and the control field with no CC or grazing. Soil BD samples were collected using a 5 cm diameter and 5 cm height core from 0-5 and 5-15 cm depths. Additionally, soil samples were collected from 0-5, 5-15, and 15-30 cm depths using a manual push probe to measure the soil EC and pH. The BD was conducted using the core method. Soil pH and EC was measured using a suspended sample consisting of soil (air-dried) and water (soil:water), with an Orion Star pH and EC meter. Soil surface GHG fluxes were monitored using polyvinyl chloride (PVC) static chambers (25 cm diameter x 15 cm height) installed in the field. Gas samples were taken daily in 2016, and weekly, depending on weather conditions, in 2017. The results showed that grazing significantly increased soil pH and EC for all depths. The grazing treatment significantly decreased soil BD for the lower depth. Legume CC significantly decreased pH for all depths, while grass CC decreased pH for the lower two depths. Legume CC significantly decreased EC at the surface and lower depth, while grass CC only lowered EC at the lower depth. The CC treatment showed no significant effect on BD at any depth. Grazing treatment showed no significant results for CO2 or CH4 fluxes for either sampling year. Grazing did not show any effect on N2O fluxes for 2016, but significantly increased fluxes during 2017. Neither CC treatment had any effects on N2O nor CH4 fluxes. However, in 2016, the legume CC significantly increased CO2 emissions and both CC treatments increased CO2 fluxes compared to fallow (control) for the 2017 season. Time effects on soil CH4 fluxes were not significant, however, were significant for CO2 and N2O fluxes. Soil CO2 and N2O fluxes increased as soil and air temperature increased, and soil moisture increased. The present study concluded that grazing significantly impacted the selected soil properties such as pH, EC, and BD, however, CCs are less likely to impact the selected properties in the short-term (first year of study). The grazing treatment significantly increased soil N2O fluxes but did not impact soil CO2 and CH4 fluxes. The CC treatment significantly increased soil CO2 fluxes compared to the fallow but did not impact soil CH4 and N2O fluxes. Time significantly impacted soil CO2 and N2O fluxes but did not impact CH4 fluxes. A positive correlation between CO2 and N2O fluxes, soil and air temperature, and soil moisture was identified. Since some soil properties and GHG emissions were negatively impacted by the grazing and CC in the ICLS during this short term study, further research for the long-term effects of grazing and CC should be conducted.

Library of Congress Subject Headings

Integrated agricultural systems -- Environmental aspects -- South Dakota.
Greenhouse gases.
Cropping systems.
Grazing.
Crops and soils.

Description

Includes bibliographical references (pages 38-44)

Format

application/pdf

Number of Pages

91

Publisher

South Dakota State University

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Rights Statement

In Copyright