Soil Bin and Field Tests of an On-The-Go Soil Strength Profile Sensor

Abstract

An on-the-go soil strength profile sensor (SSPS) was previously developed to measure the within-field spatial variability in soil strength at five evenly spaced depths up to 50 cm. In this article, performance of the SSPS was evaluated using soil bin and field data. First, the SSPS was tested in a soil bin at different depths (10, 20, and 30 cm), forward speeds (from 0.5 to 3.0 m s-1), and compaction levels (high and low). Second, data were collected in two fields having variable soil texture, bulk density, and water content. Prismatic soil strength index (PSSI, defined as force divided by the base area of the horizontally operating prismatic tip) and penetrometer cone index were measured at five depths (10, 20, 30, 40, and 50 cm) across entire fields and also more intensively in four 10 10 m areas selected for soil texture differences. Auxiliary data collected were soil bulk density, soil water content, and apparent soil electrical conductivity (ECa). When the SSPS was tested in the soil bin, increases in PSSI with speed were less than 15% from 0.5 to 3.0 m s-1 operating speed. Based on soil bin results, we selected 1.5 m s-1 as a maximum field data collection speed, below which speed effects on PSSI were deemed negligible. Mean PSSI values collected in adjacent, parallel transects were not statistically different, confirming the repeatability and stability of soil strength sensing with the SSPS. Field data showed that, in general, PSSI was higher at locations with lower ECa, lower water content, and greater bulk density. Results of stepwise multiple linear regression showed that variability in PSSI was better explained when interactions among the soil variables were included as independent variables and when data were grouped into subsets by depth and/or ECa level. Over entire fields, R2 values for estimating PSSI were 0.66 and 0.61 for a claypan soil field and a flood plain field, respectively. These results will be useful for interpreting PSSI and for future applications of the SSPS in crop management, e.g., delineation of highly compacted within-field areas and control of variable tillage operations.