Why are soil fumigants typically covered with a plastic tarp?

Soil fumigants are typically covered with a plastic tarp to maintain gas concentration. This practice is crucial because soil fumigants work effectively when they are allowed to penetrate the soil and create a controlled atmosphere that is toxic to pests. Covering the treated area with a plastic tarp helps to trap the fumigant gases close to the soil surface, preventing them from dissipating into the atmosphere. This ensures that a sufficient concentration of the fumigant remains in the soil for an adequate amount of time to achieve the desired pest control, thereby improving the effectiveness of the treatment.

Maintaining the gas concentration is essential for proper pest management, as lower concentrations may not effectively eradicate target pests and could lead to resistance development over time. By keeping the tarp in place, the efficacy of the fumigation is maximized, providing better outcomes for plant health and pest control.

The other options, while relevant to soil treatment considerations, do not directly address the primary reason for the use of a tarp in this context.