A potential new method of steam treatment for the control of soil-borne diseases, insects and weeds in sustainable crop production
A series of experiments were conducted to determine the potential of a new method of steam treatment for the control of soil-borne diseases, insects and weeds in sustainable crop production. The new method involved rapidly heating a bed of prepared soil on a porous base by passing an upward flow of steam through it. The aim was to determine whether the new method would be suitable for use in a field machine, making large-scale field steaming practically and economically viable. In the first experiments, the feasibility of the new method was tested. It was shown that it was an effective and rapid way in which a soil bed could be steamed. However, for some soils at, or near, permanent wilting point, the entrainment of aggregates in the steam flow was shown to be a problem. The second series of experiments showed that the key factor determining the flow rate at which aggregate entrainment occurred was the mean aggregate diameter of the soil being treated. The third series of experiments examined the rate at which heated soil would cool when placed in the field. It was shown that where there was contact with unheated field soil, cooling was very rapid. The final series of experiments investigated the effects of the new steaming method on the soil. A three minute steaming time was used to account for the short time it had been shown some of the heated soil would remain at steam temperature when replaced in the field. The effects of the new method, including the effectiveness of disinfection, were shown to be similar to those of a conventional steam treatment. It was concluded that the new steaming method was an effective way to steam treat soil and should be suitable for use in a field machine.