Submitted to: International Conference on Precision Agriculture Abstracts & Proceedings
Publication Type: Proceedings
Publication Acceptance Date: 5/2/2008
Publication Date: 7/21/2008
Citation: Palm, H.L., Stelzer, H.E., Sudduth, K.A., Kitchen, N.R., Drummond, S.T. 2008. Soil electrical conductivity as a management tool in precision forestry. In. Proceedings of the 9th International Conference on Precision Agriculture, July 20-23, 2008, Denver, Colorado. 2008 CDROM.
Interpretive Summary: As crop producers have adopted precision agriculture over the past several years, they have learned much about how crop production varies within fields and what may be causing those variations. An almost universal observation is that crop variability is strongly related to variability in those soil properties that influence how much water is available to the plants. In many cases, those soil properties are strongly related to soil electrical conductivity (EC), which can be quickly mapped using commercially available sensors. In this study, we investigated whether tree growth could also be related to EC. Data collected on two tree plantations in central Missouri showed that growth rates were strongly related to soil EC. EC maps provided better information on land suitability for tree production than did the normally used NRCS soil survey maps, because EC was able to identify small areas of different soils that are not shown on standard soil maps. This research may benefit landowners and foresters by providing an approach they can use for tree management decisions on variable soils.
Technical Abstract: Apparent soil electrical conductivity (ECa) is a useful measurement and indicator of relative productivity of agronomic crops on some soil types. In non-saline soils, spatial variation in soil ECa is strongly related to texture, topsoil depth and profile variations; factors which spatially correlate with crop yields. Highly eroded fields typically show significant ECa differences related to landscape, with highest ECa on eroded side-slopes, medium readings on summits, and lowest readings at toe-slopes. Mapped ECa and grain yield data typically show striking similarity, especially for the claypan soils and rolling hills of northern Missouri. Thousands of acres of cropland enrolled in the Conservation Reserve Program (CRP) have been planted with hardwood trees such as black walnut. Casual observation of these plantings reveals significant spatial variability in tree survival and tree size. Our objective in this study was to see if sensor-measured ECa is correlated to tree growth rate. Soil ECa was measured on two plantations in Saline County, MO using commercially available sensors. Trees were geo-referenced with sub-meter accuracy and growth rates were measured as height and diameter at breast height (DBH). At both plantations, growth rates of trees showed strong correlation to soil ECa. Soil ECa maps provide higher resolution than the commonly available Order II soil survey maps. Soil ECa of a tree-planted CRP field can usually be mapped using equipment pulled by a tractor or ATV. Measurements in a densely forested area may be obtained with a hand-carried device. Soil ECa mapping can enable precision forestry management by providing guidance as to which tree or shrub species is most suited for planting on highly variable sites.