Control of soil water potential using negative pressure water circulation technique

Abstract

The negative pressure water circulation technique (abbreviated as NEWCIRC) had been developed as a new technique for the control of the soil moisture conditions (Lipiec, et al. 1988: Soil Sci. Plant Nutr., 34, 417–428). In this report, the factors which influenced the hydrostatic pressure of the NEWCIRC system were examined and some guidelines were formulated to control the soil moisture conditions using this technique. Water at a negative pressure was obtained by the reduction of the air pressure in the water reservoir and the water was supplied to the soil through a ceramic tube wall. However frequently, the values of the soil water potential in the pots were not equal to those of the water in the reservoir due to the influence of water circulation which produced a pressure gradient along the water circulation system. Therefore it was considered that the hydrostatic pressure of the NEWCIRC system depended on the hydrostatic pressure of the water reservoir and the pressure difference caused by the water circulation (i.e. pump pressure) and that it was also affected by the relative positions of the pump, the reservoir, and the pots in the system. From these analyses it was deduced that uniform soil moisture conditions in several soil pots could be obtained by the use of a thick conductive pipe and also by the parallel arrangement of the pots in the circulation system due to the reduction of the flow velocity and the pressure gradient. On the contrary, a wide pressure range was attained by using a fine and long conductive pipe. The latter enabled the simultaneous development of several soil water potential levels in the soil pots linked in series. © 1991 Taylor & Francis Group, LLC.