2010 Annual Report
Planned the final phase of 2-D chamber experiments which will be use of HDPE and VIF treatments in chamber studies using local (UC Riverside) soil to study 1,3-D and chloropicrin emissions under drip irrigation. This experiment will serve as a bridging study between the field plot studies (carried out Summer 2009 on UC Riverside campus), and the laboratory studies using the Buttonwillow soil. Completion of all chemical analysis from Summer 2009 raised-bed field study samples (XAD4 and charcoal tube samples). The analysis of all associated data has been completed. Finalized the analysis and interpretation of data from Summer 2009 raised-bed field study.
Modified a finite difference solution to water, fumigant and heat transport to allow simulating field relevant conditions. The modifications include the addition of a second-order reaction process to enable simulating the reaction of ammonium thiosulfate (C_ats) with 1,3-D and chloropicrin. Second-order reaction was implemented by adding the following equation to the finite difference solution: dC/dt = -k12 C C_ats, where C is the fumigant concentration and k12 is the second-order reaction term. For preliminary testing, a value for k12 was obtained from experiments reported in the literature. Experiments are being conducted to obtain the k12 value for the Buttonwillow soil.
The computer code was also modified to allow changes in soil and chemical properties with depth. This is needed to simulate the addition of organic material into the surface soil layer, since high degradation rates were observed in the upper 15 cm, compared to degradation below.
The model was fully tested by comparing to existing analytical solutions (Yates, 2009) and by comparing simulations of water transport, heat transport and chemical transport with Hydrus 1D and/or Hydrus 2D. The comparisons demonstrate that the finite difference solution was correctly programmed and implemented.
Simulations were conducted that compared emission rates for point and shank injection. Accurate comparisons require that the simulation reflect the actual conditions that occurred during the laboratory and field study. It was found that shank injection produced more accurate emission profiles compared to point injections. For shank injection, the presence of a soil fracture leads to more spreading and higher emissions.
This research provides important information on obtaining emission estimates in a cost-effective manner.