Automation of the Water‐Drop Method for Soil Aggregate Stability Analysis

Abstract

The water‐drop method (WDM) is a long‐established and excellent means of measuring soil aggregate stability. While the WDM is very reliable, it has a drawback in that it requires manual observation of aggregate breakdown and a manual count of the number of water drops required to disperse a soil aggregate. This makes the method inconvenient and prone to error. To avoid this drawback, we propose a procedure that utilizes digital observations of aggregate breakdown and electronic recording of the water‐drop count. In this procedure, water drops from a Mariotte's tube pass through an electronic device that records the passage of each drop. The impact of water drops on the soil aggregate is digitally recorded with a camcorder. From the drop count and aggregate breakdown records, the number of water drops that strike an aggregate until it is dispersed can be determined. This procedure was evaluated using soil samples from the surface of four different soils. With the automated method, we determined the number of 4.3‐mm‐diam. water drops, each having energy of 1.67 mJ, required to destroy a 4.00‐ to 4.75‐mm‐diam. aggregate, premoistened to a matric suction of 10 kPa, until it passed through a 2.8‐mm sieve. The WDM was conducted both manually and with the automated method and the results were compared using analysis of variance (ANOVA). Twenty aggregates were used for each soil in both methods. There were no significant differences (P < 0.10) between the automated and manual methods in the mean energy required to break an aggregate.