Non-isothermal fate and transport of drip-applied fumigants in plastic-mulched soil beds: Model development and verification

• Main Author: Ha, Wonsook
• Format: Dissertation
• Language: English
• Subjects: agriculture, soil science
• ISBN: 0542755920; 9780542755927

Plastic mulched soil beds are commonly used in Florida and California to grow vegetables and horticultural crops under controlled conditions. Currently, many research teams in the United States are investigating a number of soil fumigants to serve as an alternative to methyl bromide. Many of these alternative fumigants are applied with drip irrigation method to the soil beds. One such soil fumigant is MITC (Methyl Isothiocyanate). A numerical model was developed here to describe the fate and transport of fumigants in plastic-mulched soil beds under non-isothermal conditions. The two-dimensional model was based on coupled heat and water flow, and chemical transport. A number of critical temperature-dependent processes were utilized in the model. Temperature dependence of sorption, volatilization, and degradation processes were used in the model. MITC fumigation field data from California were used to test and evaluate the model. From the comparison of modeling results and field data, simulation results yielded a lower NRMSE (normalized root mean square error) than isothermal modeling results, indicating that non-isothermal modeling provided improved description of the experimental data. Most fumigant fate and transport processes appear to be affected by temperature both directly and indirectly. The degradation coefficient was the most sensitive parameter and Henry's constant and diffusion coefficient were the least sensitive parameters in the model. Results from this research revealed the following new information: (1) The gaseous MITC distribution was highly affected by the soil water content distribution in the soil bed, (2) Inclusion of micrometeorological factor in the model was successful to depict unevenly heated soil bed during the day time, and (3) The model could suggest the optimum application criteria of application rate and time by investigating hypothetically simulated conditions.