Document Type

Dissertation - Open Access

Award Date

2017

Degree Name

Doctor of Philosophy (PhD)

Department

Agronomy, Horticulture, and Plant Science

First Advisor

Sandeep Kumar

Abstract

Switchgrass (Panicum virgatum L.) production for biofuels has potential economic values. It can also improve soil properties and perform better under marginal lands than the other major biomass crops. However, little is known about its potential ecological impacts assessed in terms of soils, water, and air quality in the northern Great Plains region of United States of America. The objectives of this study were to (i) evaluate the impacts of nitrogen fertilization rate (N rate) and landscape position on soil pH, soil organic carbon (SOC), total nitrogen (TN), bulk density (ρb), and phosphorus (P) in switchgrass field; (ii) assess the impacts of the N rate and landscape position on dissolved organic carbon (DOC) leaching in switchgrass land; (iii) evaluate the effects of the N rate and landscape position on N-dynamics that includes soil nitrate (NO3 -), NO3 - leaching, and soil nitrous oxide (N2O) fluxes from switchgrass field; (iv) simulate the long-term impacts of future temperature and precipitation changes using DAYCENT model on soil carbon dioxide (CO2) fluxes from switchgrass land; and (v) predict the long-term impacts of switchgrass production on the SOC, NO3 -, water-filled pore space (WFPS), CO2 and N2O fluxes for switchgrass fields under changing climatic scenarios using the DAYCENT models. The experiment was a split-plot design with 4 replications, 3 N rates (low, 0 kg N ha-1; medium, 56 kg N ha-1; and high, 112 kg N ha-1), and 3 landscape positions (shoulder, backslope, and footslope) in South Dakota, USA. This study showed that N rate did not impact soil pH, SOC, TN, ρb, SOC stock, and P, however, landscape position significantly impacted the soil properties. The SOC, TN, and Pb at the footslope were significantly higher than that of the shoulder and backslope. The ρb at the footslope was significantly lower than the shoulder and backslope. The SOC and TN values at the 0- to 5-cm depth increased from 2009 to 2013. The SOC was significantly influenced by year under the high and medium N rates at the 0- to 5-cm depth. The average daily DOC contents at the backslope (6.45 mg L-1) were significantly lower than that at the shoulder (8.38 mg L-1) and footslope (8.95 mg L-1). The N rate significantly impacted the soil NO3 -. At the 0- to 5-cm depth, the mean soil NO3 - contents under the high N rate (0.72 mg kg-1) were significantly lower than those of the medium (2.28 mg kg-1) and the low N (3.16 mg kg-1) rates in 2010. The NO3 - contents under the low N rate were 68% higher than that of the high N rate in 2013. The N rate significantly impacted the soil surface N2O fluxes. The annual mean soil N2O fluxes under the high N rate were 30% higher than those under the low N rate for 2014. However, the N rate did not impact NO3 - leaching. The soil NO3 -, NO3 - leaching and N2O fluxes at the footslope position were significantly higher than the other positions in some observed years. The N rate significantly impacted the switchgrass biomass yield. The yield from 2009 to 2015 under the high and medium N rates (high N rate > medium N rate) was significantly higher than that of the low N rate. The DAYCENT modeling results provided satisfactory calibration and validation by using the measured high-frequency soil CO2 fluxes from the switchgrass field from 2010 to 2013. The simulated CO2 fluxes from the switchgrass land under the different changing climate scenarios were not significantly different. To further compare the soils and environmental parameters among different N rates and positions, another 12 DAYCENT models under the high, medium, and low N rates at shoulder and footslope positions were developed using the measured CO2 and N2O fluxes for 2010 through 2015. The predicted SOC, soil NO3 -, CO2 and N2O fluxes at the footslope were significantly higher than that of the shoulder. Generally, the predicted SOC, soil NO3 -, CO2 and N2O fluxes under the higher N rates were higher than that under the low N rate. Results from this study concluded that the switchgrass seeded on marginally yielding croplands can act as a sustainable bioenergy crop through improving and maintaining soil properties, storing N nutrient, and reducing NO3 - leaching. Furthermore, the medium N fertilization rate (56 kg N ha-1) was the optimal rate for the switchgrass fields to increase the biomass yield, improve soil properties, and reduce the soil N2O emissions and NO3 - leaching.

Description

Includes bibliographical references

Format

application/pdf

Number of Pages

398

Publisher

South Dakota State University

Rights

Copyright © 2017 Liming Lai

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