Assessing temporal stability and spatial variability of soil water patterns with implications for precision water management

The temporal stability of soil water content patterns may have profound implications for precision agriculture in general and water management in particular. Spatio-temporal variability in soil water was assessed over four fields in a two-year potato (Solanum tuberosum L.) and barley (Hordeum vulgare L.) rotation to determine the potato yield implications and the potential for precision water management based on a stable spatial pattern of soil water. A hammer-driven time domain reflectometry probe was used to measure soil water content repeatedly along 10 transects. Irrigated, un-irrigated, and late irrigated treatments were employed. The temporally stable soil water pattern was mapped and compared with elevation and soil particle size classifications. A temporal stability model explained 47% of the observed variability in soil water content. An additional 20% of the variability was attributed to random measurement error. Calibrated in 2002, the model predicted water content (root mean square error of 0.05 m3 m-3) along transects in 2003 from a single measurement at the field edge. Fieldscale trends and extended (>100 m) wet and dry segments were observed along transects. Coarser particle size class soils were generally drier. Potato yield increased linearly with water content in un-irrigated areas. Yield was comparatively high in the drier areas for the irrigated treatment but was highly variable and frequently poor in the wetter areas. For the lateirrigated treatment, a strong yield response to added water was evident in the dry areas; however, the yield response was neutral to negative in the wetter areas. Knowledge of the underlying stable soil water distribution could provide a useful basis for precision water management.