Energy Efficient Soil Disinfestation by Microwaves

A major obstacle prohibiting the use of microwaves for soil disinfection and disinfestation is the large amount of energy required to obtain sufficient results. The present work presents an experimental study of the effect of initial soil temperature and soil moisture on energy consumption by application of microwaves for soil disinfection. All experiments were carried out by using a microwave generator of a nominal power output of 900 W. The ultra-high-frequency field (2450±2 MHz) was produced by a magnetron tube and channelled through a metal waveguide. The output opening of the waveguide was placed directly on the soil surface. It was found that a soil with 15% moisture content (w.b.) and an initial temperature of 20°C requires energy to be heated at a depth of 10 cm up to 61°C which is 3·2 times more than the energy required to heat the soil up to 5 cm depth at the same initial temperature. In general, the conversion of electric energy to useful microwave energy absorbed in the upper 10 cm soil was no more than 13% efficient in this field application. Heating a soil of 15% moisture content (w.b.), when the initial soil temperature is 40°C, requires 14 kWh/m2or 42% less energy than the soil with the same moisture content but at 20°C initial soil temperature. When the initial temperature is 40°C and the soil moisture is 5·5% (w.b.) only 7·4 kWh/m2is required. It is concluded that humidity of the soil and initial soil temperature are critical for a low-cost use of microwaves for soil disinfestation, and a combination of solarization and microwaves is proposed as an energy efficient technique of using microwaves for soil disinfestation.