Submitted to: Transactions of the ASAE
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 2/23/2004
Publication Date: 6/30/2004
Citation: Hummel, J.W., Ahmad, I.S., Newman, S.C., Sudduth, K.A., Drummond, S.T. 2004. Simultaneous soil moisture and cone index measurement. Transactions of the American Society of Agricultural Engineers. 47(3):607-618. Interpretive Summary: As agricultural tractors and field equipment get larger, the concern about soil compaction increases. Larger land areas being farmed by the same set of machinery increases the possibility that field operation will occur when soil is easily compacted. Instrumentation is needed to measure when soil is compacted to a level that, without additional tillage, will restrict crop root growth. Furthermore, instrumentation is needed that can acquire data across a range of soil types and soil moisture contents and provide a measure of compaction that is independent of soil moisture content. This paper reports on laboratory testing of a novel instrument consisting of a USDA-Agricultural Research Service designed and patented soil moisture sensor integrated with a soil cone penetrometer. The instrument uses a fiber optic bundle to transmit light down the penetrometer shaft and through a specially designed penetrometer cone onto the soil surface. Light reflected from the soil is transmitted back up the shaft to the soil surface for analysis and moisture prediction. Soil cone index, measured in the same manner as with a conventional penetrometer, can then be adjusted to a standard soil moisture level. This laboratory study reports on the development of a cone index/moisture relationship for three surface agricultural soils in Illinois and indicates that soil moisture might be used to adjust soil cone index to a standard moisture content, allowing comparison of cone indices over time and space. Commercialization of this concept could significantly increase the usefulness of soil penetration resistance data and lead to reduced primary tillage when used to measure soil compaction. Reduced tillage will impact producers through savings in labor, fuel, and machinery costs and will benefit consumers through reduced erosion and sedimentation.
Technical Abstract: Soil compaction can restrict root growth and water infiltration resulting in yield reduction. Maps of yield monitor data aid in visualization of variations in yield without identifying underlying factors for these variations. Soil penetration resistance can help identify areas where soil physical characteristics are negatively impacting yield. However, penetration resistance is a function of moisture content and soil type as well as compaction. A standard penetrometer cone was modified to collect near-infrared spectral reflectance as the cone was being inserted into the soil. Algorithms were developed to estimate soil moisture content and to predict soil cone index. The instrument was tested in the laboratory on a selection of soil types with varying moisture contents using stepwise and continuous probe insertions. Soil cone index, soil moisture, density, and clay content were significant variables in predicting soil cone index at a different, lower moisture tension level.