For trickle irrigation systems to deliver improved water and nutrient use efficiency,
distance between emitters, emitter flow rates and, for buried tape, the depth of burial
must be matched to the soil's wetting characteristics and the amount and timing of water
to be supplied to the crop. Wetting patterns were calculated from hydraulic properties of
two groups of soils, covering a wide range of textures and soil hydraulic properties. The
groups differed in the degree of field structure that was retained in the soils. The
hydraulic properties of each of the soils in the first group were actually the mean of up
to 400 samples that had been sieved before their hydraulic properties were determined.
The second group consisted of 18 soils from Bundaberg, that had their hydraulic
properties determined either in the field or on intact cores, so retained the effects of field structure. Wetting patterns were determined for conditions commonly associated with daily irrigation applications. In the first group, the wetted radius increased and depth of wetting below the emitter decreased with increasing clay, as is commonly accepted. In the second group however, there was no such relationship between wetting patterns and texture. For example, four soils with the same classification and texture had as great a variation in wetting pattern as did all 11 soils in the first group, indicating the considerable impact of field structure on wetting patterns. Thus soil type and/or texture are unreliable predictors of wetting patterns, and there is no justification for having different emitter spacings in different soil textures. The results also suggest that (1) emitter spacings in common use are generally too large to allow complete wetting along the row between emitters, and (2) the depth of wetting may be greater than the active root-zone in many soils, resulting in losses of water and chemicals below the root-zone. Overall, the results show that site-specific information is required on wetting patterns or soil hydraulic properties to design efficient trickle irrigation systems.