Pandey, Aditi (2018-08). Quantification of Soil Ecosystem Services from Organic Fertilized Rice Production in Beaumont, Texas. Master's Thesis. Thesis uri icon

abstract

  • The socio-economic implications of replacing synthetic fertilizer with an organic fertilizer or soil amendment have been evaluated for rice farmers and their community. We approach this knowledge gap by linking alterations in the soil biophysical properties with meaningful benefit-relevant soil ecosystem services produced in rice paddies. The Denitrification and Decomposition (DNDC) model simulated greenhouse pot experiment from Beaumont, Texas was validated with grain yield, methane and dissolved soil organic C data from a three-factorial randomized experiment with source (Nature Safe (13%) and urea) and rates of N fertilizers (untreated control, 50, 100, 150, 200, and 250 kg N ha-1) as independent variables. Transitioning to organic fertilizer resulted in lower grain yields, higher methane and soil organic C storage; however, no statistical significance was found between treatments. Next, DNDC simulations were calibrated with previously reported field rice yields and methane emissions from conventional and organic amended rice farming near Beaumont, TX. The model was used to simulate single and 22-year simulations. Significant treatment effect was observed for methane emissions, grain yield and soil C and N cycling. A causal chain approach was used to identify relevant beneficial indicators from soil ecosystem services quantified using DNDC simulations. Therefore, changes in soil C cycles were linked to the social cost of C, rice grain yields, potential property losses to flooding events, suspended solids visible in local waterways and aquatic biodiversity. Similarly, changes in soil organic N cycling were linked to reduction in N input for the next crop cycle, social cost of C, capacity of soil to sustain a double crop, and evasion of eutrophication. Adopting organic amendments improved soil health and ecosystem services but also increased methane and nitrous oxide emissions and the overall global warming potential. Transitioning to organic amendments should be made with the understanding that the tradeoff is increased emissions per hectare comparable to driving a 2015 Ford F150 model for 15,000 miles a year. Finally, the DNDC model has several limitations and needs to include holistic measurements of soil biological, physical and chemical changes to be useful for soil ecosystem services quantification.

publication date

  • August 2018