Submitted to: Agricultural Water Management
Publication Type: Peer reviewed journal
Publication Acceptance Date: 9/23/2004
Publication Date: 4/2/2005
Citation: Starr, G.C. 2005. Assessing temporal stability and spatial variability of soil water patterns with implications for precision water management. Agricultural Water Management. Volume 72, Issue 3, 2 Apr 2005, pages 223-243 Interpretive Summary: Effective and efficient management of water is vitally important in many agricultural settings. Conserving water has benefits for society, the environment, and agriculture. It is increasingly recognized that although soil water content changes over time, the spacial pattern of this variability is fairly constant. This study investigated the possibility of mapping that stable soil water pattern and adjusting irrigation applications accordingly. This approach to water management is feasible provided the pattern of variability is on a manageable spatial scale and provided there is a demonstrable yield response to the stable soil water pattern. We found a very stable water content pattern in several potato fields in north-central Maine. The yield data suggest that the drier parts of a field will respond very well to irrigation but the wetter parts of the field can experience a yield decrease caused by excessive water. Maps of the stable water content pattern, along with elevation and soil maps should provide powerful tools for evaluating water management strategies. Although considerable effort is required to measure the water pattern, the temporal stability of the pattern suggests that this procedure need not be repeated often, if at all. These water maps can then be used to design intelligent and environmentally sound irrigation systems that conserve water, while increasing yield.
Technical Abstract: The temporal stability of soil water content patterns may have profound implications for precision agriculture in general and water management in particular. However, it needs to be demonstrated that the scale of spatio-temporal variability is appropriate for precision farm management and that a yield response to stable soil water content exists. A hammer driven time domain reflectometry probe was used to measure soil water content repeatedly along ten transects covering four fields in a two year potato-barley rotation. Irrigated, un-irrigated, and late irrigated treatments were employed. The temporally stable soil water pattern was mapped and compared with elevation and soil texture maps. Temporal stability explained 47% of the observed variability in soil water content. An additional 20% of the variability was attributed to random measurement error. Field-scale trends and extended (>100m) wet and dry segments were observed along transects and these trends persisted from one year to the next despite the change in crops. Coarser textured soils were generally drier. In fields where texture was consistent, water content generally declined with elevation. Yield increased uniformly with water content in un-irrigated transects. Yield was consistently high in the dry areas for the irrigated treatment but was highly variable and frequently poor in the wetter areas. For the Late-Irrigated treatment in 2002, a strong yield response to added water was evident in the dry areas. The response was neutral in 2003 and negative in 2002 in the wetter areas. There appear to be advantages in both water savings and yield if a pattern of irrigation water application is designed to fit the underlying stable soil water distribution map.