Evaluation of the moisture equivalent soil test for irrigation management

Previous research demonstrated that the moisture equivalent (ME) soil test measured at about ‐80 kPa reflects soil clay and organic matter contents, exhibits good precision, and is well correlated to the ‐33 kPa pressure plate estimate of field capacity. However, data to guide interpretation of the ME results in irrigation management are lacking. In the present research, soil mixes comprising 45 to 100% sand, 0 to 50% clay, and 0 to 5% peat by volume were used to determine the effects of soil composition on ME measured at either ‐13 or ‐80 kpa. The plant available water capacity (AWC) was determined by growing plants in pots containing the soil mixes. Volumetric ME measurements at either ‐13 or ‐80 kPa increased linearly with clay content, as did the volumetric water content at wilting point (WP). Hence, the estimated AWC was essentially constant across the entire range tested. If WP and AWC estimates from this greenhouse study reflect field conditions, the results do not support soil testing to guide differential irrigation management based on soil texture.