A Study of Lateral Moisture Migration in Container Mediums

Abstract

If Volumetric Water Content (VWC) sensors are to be used in container-grown plants todecide When to irrigate? and How much to irrigate?, then the lag time from the time water is added toa container at the surface until additional moisture is detected by the sensors must be known. Whereshould sensors be located? The objectives of the experiment were: (1) to measure the distance andspeed of water migration in container mediums in a laboratory setting, (2) to compare water migration intwo types of container mediums, a grower mix and a commercial mix, and (3) to observe waterdistribution directions and patterns. While using a grower designed, custom made mix with VWC = 25.5%,106 min were required for the water to migrate 7 in. for an average velocity of 0.066 in./min. When thissame container medium was dried to 1.8 % VWC, the hygroscopic capacity of the mix was apparentlyseverely reduced. Lateral water migration was adversely impeded in some directions and magnified inothers. The probe located 3 in. to the left sensed water after only 1 min, which required an averagevelocity of 3.5 in./min. Meanwhile, the probe located 3 in. to the right of center required 32 min for thewater to travel 3 in. laterally (V = 0.109 in./min). This implies the water traveled to the left 32 times asfast as it traveled to the right. The direction, distance and speed of lateral moisture movement in containermediums are apparently not predictable.