Development of mobile soil rotary steam disinfection machine

Abstract: China has been a great producer and consumer of vegetables all the time, and with the continuous development of vegetable cultivation, a series of problems have appeared, which have caused the tremendous pressure on the soil. For example, a tremendous use of fertilizer has led to many terrible results, like soil nutrient imbalance, soil continuous cropping barriers, imbalance of soil physical and chemical properties, soil consolidation, and so on. Every issue would cause serious damages to vegetable growth, yield and quality. In order to deal with the problem of vegetable planting caused by soil continuous cropping obstacle, a kind of steam disinfection machine was designed. This machine combined the rotary tillage device with the steam sterilizer effectively, and made it possible to complete the disinfection work while doing the soil rotary tillage. It was mainly composed of 6 parts: the rotary tiller, the steam generator, the water supply device, the steam delivery system, the disinfection cover and the detachable disinfection capillary. Compared with chemical disinfection, soil steam disinfestation was an ecological technique used in intensive agriculture to reduce soil pests before planting crops, which had the advantages of safe operation. Soil steam disinfection made high temperature water vapor into the soil, and could kill most bacterias and weeds in the soil so as to achieve the effect of disinfection. Also, high temperature steam sent the residual nitrogen and phosphorus under the effective tillage layer through the pore of the soil; at this time, the pore of the soil would also be heated by the high temperature water vapor, and the pore of the soil was enlarged with the dredging of the water vapor simultaneously. Therefore, this soil vapor disinfection increased the permeability and drainage of the soil, which was beneficial to the improvement of soil texture. By the way, it could be learnt through the analysis of the heat balance that the steam power required for the soil disinfection at 60 ℃ was 87.78 kW when the soil body was 120 cm wide and 15 cm deep, while when the steam generator outlet pressure of the steam sterilizer was 0.6 MPa and the temperature was 158.86 ℃, the steam power of the steam generator was 97.35 kW and the system loss was 0.61 kW, which could meet the heat demand of soil disinfection. And through the plot experiments, the main parameters affecting the steam disinfection performance of soil, including steam pressure, speed of machine running, diameter of capillary tube and spacing between tubes were determined, and relevant theoretical analysis was performed at the same time. Plot experiments showed that under the steam pressure of 0.6 MPa, the temperature of 158.86 ℃,and the rotary working speed of 0.035 m/s, 15 cm depth of soil temperature can reach 58.9-70.6 ℃ under the condition of the capillary tube diameter of 15 mm and separation distance of 180 mm. This study provides not only a reference for further improving the performance of soil steam sterilizer, but also a choice for the farmers using the soil steam disinfection system.