Pesticide is applied to a 10 ha (hectare) field at an average rate of 1 kg/ha every month. The soil is regarded as 20 cm deep and well-mixed. The pesticide evaporates at a rate of 2% of the amount present per day and it degrades microbially with a rate constant of 0.05 day-1. What will be the steady state concentration of pesticide in g/m3 and in unit of g/g, assuming the soil density as 2500 kg/m3.
To find the steady-state concentration of pesticide in g/m3, we need to consider the amount of pesticide that accumulates and the amount that is lost due to evaporation and degradation.
First, let's calculate the amount of pesticide added to the field each month. The field area is 10 ha, and the application rate is 1 kg/ha. Therefore, the total amount of pesticide applied each month is:
Total Amount of Pesticide Applied = 10 ha * 1 kg/ha = 10 kg
Next, let's convert the depth of the soil to meters. The soil depth is given as 20 cm, which is equal to 0.2 meters.
To determine the total volume of soil in the field, we multiply the area of the field by the depth of the soil:
Total Volume of Soil = 10 ha * 0.2 m = 2,000 m3
To find the steady-state concentration of pesticide in g/m3, we divide the total amount of pesticide applied by the total volume of soil:
Steady-State Concentration = Total Amount of Pesticide Applied / Total Volume of Soil
= 10 kg / 2,000 m3
To convert the concentration from kg/m3 to g/m3, we multiply the concentration by 1,000:
Steady-State Concentration = (10 kg / 2,000 m3) * 1,000
= 5 g/m3
Therefore, the steady-state concentration of pesticide in g/m3 is 5 g/m3.
To find the steady-state concentration of pesticide in g/g, we need to consider the soil density. The soil density is given as 2500 kg/m3.
First, we need to convert the steady-state concentration from g/m3 to kg/m3:
Steady-State Concentration (kg/m3) = 5 g/m3 / 1000
= 0.005 kg/m3
To find the concentration in g/g, we divide the concentration in kg/m3 by the soil density:
Steady-State Concentration (g/g) = 0.005 kg/m3 / 2500 kg/m3
= 0.000002 g/g
Therefore, the steady-state concentration of pesticide in g/g is 0.000002 g/g.