MOISTURE EQUIVALENT AS A ROUTINE SOIL PHYSICAL TEST TO GUIDE IRRIGATION MANAGEMENT

Although water retention and movement in soils determine both the need for irrigation and the loss of nitrogen (N) from agricultural systems , soil physical tests are generally too time-consuming for routine ana lysis by soil testing laboratories. We evaluated the potential of the Moisture Equivalent (ME) method as described by Bouyoucos for routine soil physical measurement. The method consists of saturating a sieved soil sample in a Buchner funnel, vacuum filtering the sample for 15 mi n while covered, then determining the gravimetric water content. On 72 soil samples run in triplicate, ME results were highly repeatable (CV values generally less than 3%). In addition, ME results were linearly correlated to clay and organic matter contents (R2 = 0.85) and to 33 kPa moisture content (R2 = 0.85). We conclude that the ME method is su fficiently convenient to run routinely in a soil testing laboratory, a nd sufficiently dependable to improve precision in irrigation and N ma nagement. Interpretive criteria for applying ME results will require v erification through field calibration studies.