Carbofuran is applied to a corn field at planting time in order to control corn rootworm. The application rate is 3.5 kg/ha. The soil has an organic matter (OM) content of 2% and a bulk density of 1.46 grams/cm3.
Ten days after application, a storm occurs which produces 0.5 cm of runoff, 1.5 cm of infiltration and 0.7 tonnes/ha of sediment leaving the field.
1. Estimate the amount of carbofuran remaining at the start of the storm. Use the tabulated value of the decay constant that is based on a field study.
2. Partition the remaining carbofuran between dissolved and adsorbed phases. Assume that the carbofuran is mixed in the top inch of soil and that the volumetric soil water content is 0.3.
• Determine the dissolved concentration (?g/L) and dissolved mass (kg/ha) of carbofuran.
• Determine the adsorbed concentration (?g/kg) and adsorbed mass (kg/ha).
3. Estimate the loss of carbofuran in (1) runoff, (2) sediment, and (3) leaching-ignoring retardation of the carbofuran-from the storm. Assume that the overland flow mixes to 0.5 cm depth and that the soil water content returns to 0.3 a few days after the storm. Note that the actual loss of carbofuran due to leaching will be less than this estimate since its downward movement will be retarded due to adsorption