Summary:The effect of trickle irrigation on the activity, leaching and distribution in the soil of herbicides, was studied in a model specially constructed for simulating trickle irrigation in the field, and also under field conditions.The pattern of movement of a soil‐applied herbicide in the soil under trickle irrigation paralleled, to some extent, that of the trickle water itself, but total herbicide movement was less than that of the water. Both water and herbicide distribution in the soil formed the shape of a hemisphere or cone under the trickle nozzle, the exact shape of which was determined by the soil characteristics (a narrow cone in a light soil and a wide cone in a heavy soil); cone size was determined by the amount of trickle water.Bioassays with susceptible test plants showed that effective weed control could be expected with either simazine or GS‐14259 (2‐t‐butylamino‐4‐ethylamino‐6‐methoxy‐s‐triazine =‘Caragard') only in the areas wetted by the trickle nozzle.The results showed that the pattern of distribution in the soil of simazine and GS‐14259 was similar, but there were quantitative difference
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