Soil water sensing:Implications of sensor capabilities for variable rate irrigationmanagement

摘要

Irrigation scheduling using soil water sensors aims at maintaining the soil water content in the crop root zone above a lower limit defined by the management allowed depletion (MAD) for that soil and crop, but not so wet that too much water is lost todeep percolation, evaporation and runoff or that the crop quality is impaired. To be useful for managing water to prevent over filling the soil or allowing it to dry so much that crop yield is compromised, soil water sensors must be accurate to the order of 0.02 to 0.04 inch/inch. Issues of sensor performance, numbers of sensors required for effective variable rate irrigation (VRI) management, and other factors complicating sensor application to VRI management all hamper adoption of soil water sensingsystems for VRI. An alternative to soil water sensing that may be helpful is soil bulk electrical conductivity mapping, which can delineate field zones of different soil textures if salinity is not a factor. Another alternative, soil canopy temperature sensing, has been shown to accurately reflect plant water status and thus soil water status in semi-arid and arid irrigation regions; and this method is approaching commercial availability. A combination of crop canopy temperature sensing, which effectively uses the crop as many thousands of biological soil water sensors, and a few accurate soil profile water content sensors may prove to be the most practical approach to variable rate irrigation management in many regions.