Date of Award
Master of Science
Soil Science (Soil Management)
The increase in atmospheric carbon dioxide (CO2) over the last century has led to an increased interest in soil C dynamics and sequestering C in soil. The focus of this study is to investigate CO2 emissions and soil C changes with various N application rates in a corn-soybean rotation. The study consists of seven sites across Iowa. Each experiment consists of four selected N rates of 0, 90, 180 and 225 kg ha−1 replicated four times in a randomized complete block design in a corn-soybean rotation. Soil samples were collected at 0-5, 5-10, 10-15, 15-30 and 30-60 cm increments for soil organic carbon (SOC), total soil N (TN), particulate organic matter carbon (POMC), and associated mineral fraction C (MFC). Field soil CO2 emissions from the same N rate treatments were measured during the growing season using a Li-Cor 6400 Infrared Gas Analyzer every seven to 10 days at the Boone, Floyd, and Warren sites in 2002, and Tama site in 2003. Soil laboratory incubation, microbial biomass, and N mineralization studies were conducted on the soils from Boone, Floyd, and Tama sites. Results indicated cumulative soil CO2-C emissions varied in response to N fertilization. Higher N rate treatments had lower cumulative CO2-C than the 0 kg ha−1 N rate treatment when N fertilizer was applied to the corn crop. However, N fertilizer rates of 90, 180 and 225 kg ha−1 N applied to corn the previous year showed higher cumulative CO2-C emissions than the 0 kg ha−1 N rate treatment in the soybean season. In a laboratory soil incubation study, N fertilized soils emitted significantly less CO2-C than the non-fertilized soils. Nitrogen fertilization significantly increased inorganic soil N concentration prior to a 56-day laboratory incubation. After the 56-day incubation period, inorganic soil N concentration was significantly lower for the 0 kg ha−1 N rate treatments than the higher N rate treatments. Nitrogen fertilization did not have a significant effect on microbial biomass carbon (MBC). Results indicate N fertilization does not significantly affect soil SOC, POMC, or MFC at the 0-5, 5-10, and 15-30 cm depths. Nitrogen fertilization had variable effects on crop biomass production along with TC and TN potentially returned to the soil via biomass. Overall, after 2 years of N fertilizer application to corn and one year of soybean with no N fertilizer application, no significant changes in soil SOC, POMC, and MFC were observed in the short period of time.
Marc Louis Kruse
Kruse, Marc Louis, "Effects of nitrogen fertilization on soil carbon dynamics in a corn-soybean rotation in Iowa" (2005). Retrospective Theses and Dissertations. 19699.