Measuring soil water content under turfgrass using the dual-probe heat-pulse technique

Measurements of soil water content near the soil surface often are required for efficient turfgrass water management. Experiments were conducted in a greenhouse to determine if the dual-probe heat-pulse (DPHP) technique can be used to monitor changes in soil volumetric water content (theta(v)) and turfgrass water use. 'Kentucky 31' Tall fescue (Festuca arundinacea Schreb,) was planted in 20-cm-diameter containers packed,vith Haynie sandy loam (coarse-silty, mixed, calcareous, mesic Typic Udifluvents), Water content was measured with the DPHP sensors that were placed horizontally at different depths between 1.5 and 14.4 cm from the surface in the soil column. Water content also was monitored gravimetrically from changes in container mass. Measurements started when the soil surface was covered completely by tall fescue, Hence, changes in theta(v) could be attributed entirely to water being taken up by roots of tall fescue, Daily measurements were taken over multiple 6- or 7-day drying cycles. Each drying cycle was preceded by an irrigation, and free drainage had ceased before measurements were initiated. Soil water content dropped from approximate to 0.35 to 0.10 m(3).m(-3) during each drying cycle. Correlation was excellent between theta(v) and changes in water content determined by the DPHP and gravimetric methods. Comparisons with the gravimetric method showed that the DPHP sensors could measure average container theta(v) within 0.03 m(3).m(-3) and changes in soil water content within 0.01 m(3).m(-3).