transport and degradation of herbicides in soil under different herbigation systems

the objective followed in this study was to investigate the transport and degradation of herbicides under different herbigation vs. conventional spraying systems in soil. metribuzin and potassium bromide (kbr) were applied in soil plots by four application methods, including conventional spraying without delay in initial irrigation (cs1), conventional spraying with an initial 24-h delay in irrigation (cs2), herbigation via the first irrigation (hrb1) vs. herbigation via the second irrigation (hrb2). the results indicated that the highest leaching of herbicide and kbr along with the lowest degradation of herbicide was obtained for the treatment of herbigation via first irrigation. in hrb1 treatment, herbigation, when in dry soil, caused rapid movement of kbr and herbicide within the open pores preserving the herbicide from photochemical and microbial degradation which mostly occurs at the surface soil layer. among conventional spraying methods, the first irrigation delay after chemical application, in cs2 treatment, led to herbicide diffusion to inter aggregate macrospores and as well adsorption on the organic and inorganic particles. thus, the applied herbicide did not leach out and remained at the soil surface for a longer time. remaining of a large portion of herbicide at the soil surface has led to an increase in herbicide degradation, due to the availability of a greater organic matter content, microbial population, sunlight radiation as well as moisture content.