Temperature variation in the topsoil during thermal weed control

Abstract

The paper presents analysis of temperature variation in the topsoil during thermal weed control. The study was aimed to determine the peculiarities of the technology of weed thermal control by wet saturated steam in the crop stand above the emerging seed. During thermal weed control, a high-temperature environment of 100oC is created in the plant environment seeking to heat plant tissue to a temperature of above 58oC. In such temperature, changes occur in the biological processes in plant tissue resulting in lethal outcome. Thermal weed control process using wet saturated steam (WSS) significantly differs from the flaming by gas. During the steam condensation, the high-temperature environment intensively heats not only plants but also soil surface. Consequently, in the technology of thermal weed control with water steam it is necessary to find solutions to the issues of emerging seed and seedling destruction in the soil. Experimental evidence suggests that irrespective of the WSS treatment duration, soil surface temperature is close to that of water steam and is 94.7-95.5oC. Water steam condensation process occurs on the soil surface, therefore a temperature of 58oC, which is lethal to plants, reaches deeper soil layers. The experimental findings indicate that application of WSS technology for weed control (with a thermal treatment duration of 1-3 s), destroys plants and seedlings present not only on the surface of the soil but also in the surface soil layer up to 1.5 mm depth. Simulation of temperature fields in the surface soil layer enabled us to identify the effects of soil bulk density and thermal treatment duration on the formation of temperature exceeding 58oC. [...]