Presenter: Kannan Iyyemperumal
Advisor(s): Wei Shi
Author(s): Kannan Iyyemperumal, Jim Green Jr., Daniel W. Israel, and Wei Shi
Graduate Program: Soil Science, Crop Science, Soil Science, Soil Science

Title: Soil Nitrogen Mineralization and Microbial Properties in Forages production systems: Consequences of Nitrogen Fertilizer Source and Rate

Abstract: Our objective was to determine the effects of swine lagoon effluent (SLE) and ammonium nitrate (AN) on soil N supplying capacity and microbial functional groups of N mineralizers and nitrifiers in a forage production system. We collected soils at 0 7.5 cm depth in 2004 from field plots planted with Bermuda and Tall fescue that received AN and SLE from 1999 2001 at rates equivalent to 0, 200, 400, and 600 kg available N ha-1 yr-1, respectively. Fertilization significantly (P < 0.05) increased total soil N, amino sugar N (ASN), microbial biomass N (MBN), potential N mineralization and nitrification, indicating that fertilization improved soil N supplying capacity. However, soil microbial biomass C (MBC) was greatest at the lower fertilization rate, i.e. 200 kg N ha-1 yr-1. Microbial biomass C:N ratios also decreased significantly with fertilization rates (P < 0.05), suggesting that fungal biomass declined with increased N fertilization. In comparison with AN, soils receiving SLE had lower total soil N, ASN, MBC, microbial biomass C:N ratios and potential nitrification rates. The different effects between SLE and AN, especially at higher N fertilization rates, on soil and microbial properties are likely due to changes in soil chemical properties associated with SLE application.