A Passive Application Watering System for Rangeland Plots

Abstract

Soil water is generally the most limiting factor for plant growth in arid and semiarid rangeland ecosystems. Interactions between precipitation regimes and optimum air temperatures for growth of different species often have measurable effects on peak standing herbage and species composition. Simulating multiple precipitation regimes in a single year will enhance our ability to quantify plant-environment interactions. Evaluating the seasonal effects of variation in timing and quantity of precipitation will require controlled water applications with little or no runoff. A diversity of plot watering systems has been developed for different kinds of agronomic and rangeland research. However, most of these systems were designed to simulate heavy pre- cipitation events and features of all previously described systems limit the number of plots and/or variation in site characteristics that can be included in rangeland field studies. Therefore, we developed the Passive Application Watering System (PAWS), which is composed of a graduated polyethylene application tank connected to a discharge system of polyvinyl chloride (PVC) and soaker hose subunits. It is portable and suitable for applying water over a wide range of slope, soil texture, and residual herbage conditions with little or no runoff. Application rates are controlled by the amount of hydrostatic pressure, which is determined by the head, the difference in height between the tank’s water level, and the soaker hoses. Heads of 0.1 m and 2.0 m produce application rates of 5 mm hr-1 and 40 mm hr-1 which correspond to the permeability of clay loam and silt loam, respectively. Application rates increase about 1.8 mm hr-1 +/- 0.15 SE for each 10-cm increase in head. We have successfully used the PAWS in 3 research projects on range sites with sandy and loamy soil texture classes.