Regional field study of the spatial variability of selected soil physical properties

Abstract

Soil moisture and pH levels directly affect urban tree performance. An accurate sensor to assess these soil conditions would allow arborists and urban foresters to make and evaluate management actions. These actions may then be used to improve tree species diversity and site quality. Toward this goal, twenty-one soil pH and moisture sensors were tested for their ability to accurately and precisely measure soil pH, volumetric soil moisture content (VMC), or both. This research was conducted on four different soil texture classes (loamy sand, sandy loam, clay loam, and clay) at three different moisture levels (air dry, ≈ 0.5 field capacity, and ≈ field capacity). Soil pH sensors using a glass-electrode in a 1:2 (soil:deionized water) solution were found to accurately and precisely measure soil pH (P = <0.0001; ρc = >0.95). However, sensors using metal electrodes inserted into the soil had no significant correlation to soil pH levels (P = >0.1; ρc = <0.2). When selecting a soil pH sensor, measurement method may be the most important consideration. Soil VMC sensors using time domain reflectometry and frequency domain reflectometry methods performed best (P = <0.0001; ρc = >0.76). Sensors using the electrical conductivity method were highly variable in cost, accuracy, and precision. Future work on these sensors may include field performance evaluations as well as management implications for urban sites.