Quantifying Moisture Content Near the Surface in Sand Based Putting Greens.

Managing sand-based putting greens requires adequate moisture levels throughout the rootzone while ensuring firmness of the putting surface. Accurately monitoring moisture distribution throughout the profile is critical in achieving the appropriate balance of plant health with playability. Time domain reflectometry (TDR) is an accepted technology for precisely and objectively quantifying volumetric water content (VWC) at various depths throughout the rootzone. Obtaining TDR measurements within the uppermost 2.5 to 1.2 cm offers potential for enhanced understanding of interactions between weather effects, maintenance practices, and playing conditions. However, TDR measurement depths are limited by necessary minimum rod length required to reliably produce accurate readings; current minimum rod length for portable TDR meters is 3.81 cm. The objective of this research was to estimate VWC% within the surface 2.5 and 1.2 cm. A TDR300 (Spectrum Technologies Inc.) was modified so that the penetrating depth (rather than overall length) of the 3.81 cm TDR rods were reduced. Two spacer-blocks were used to create new penetrating depths of 2.5 and 1.2 cm. In 2014 samples extracted from creeping bentgrass (Agrostis stolonifera) and ultradwarf bermudagrass (Cynodon dactylon x C. transvaalensis) sand-based putting greens were saturated and dried within the laboratory to create a range of water contents. TDR measurements at the new penetrating depths were taken in microseconds, while VWC% for each sample was calculated by weight. Regression analysis produced linear prediction equations relating modified TDR readings in microseconds to VWC% at 2.5 and 1.2 cm depths with R² values = 0.94 and 0.90 respectively. In 2015 in situ sampling compared VWC% calculated using the 2014 equations to VWC% determined by weight, producing R² = 0.9433 and 0.9184 for 2.5 and 1.2 cm respectively. These results indicate that the TDR300 can be modified to quantify moisture levels very near the putting surface of sand-based greens.