Expanding implementation of an on-line measurement system of topsoil compaction in loamy sand, loam, silt loam and silt soils

A previously developed model for on-line prediction of soil compaction indicated as bulk density (BD), was limited in use for a sandy loam field. This study was undertaken to investigate the possibility of modifying this model for new soil textures, namely loamy sand, loam, silt loam and silt soils. Using the on-line measurement system of BD, measurements were carried out in four fields with different average textures of loam, sandy loam and silt loam and silt loam/silt fields. The on-line measurement system used consisted of a subsoiler, whom draught (D) was measured with a single shear beam load cell and depth (d) was measured with a wheel gauge consisted of a swinging arm metal wheel equipped with a linear variable differential transducer (LVDT). The soil gravimetric moisture content (MC) was measured with the oven drying method. The on-line measured BID was compared with measured BD with Kopecki rings (core sampling method) (736 samples), to validate the potential use of this sensor in the new studied soil textures. Results showed that the BD model can be used for on-line measurement of soil compaction for the selected textures. It was found that the correction factor (M) of this model was mainly sensitive to variable MC, and slightly sensitive to clay content. The M at field scale varied between 0.994 (silt loam/silt soil with an average MC of 0.279 kg kg(-1)) and 1.171 (loam soil with an average MC of 0.105 kg kg(-1)). At almost the same texture, M varied between 1.171 for an average MC of 0.105 kg kg(-1) and 1.122 for an average MC of 0.186 kg kg(-1), which proves the domination of MC effect on M. The multiple linear regression (MLR) analysis (analysis of variance (ANOVA)) performed between MC and clay and M retained MC as M predictor (P < 0.001, R(2) = 0.86). This MLR resulted in similar prediction accuracy of compacted zones as compared to the linear regression model between MC and M. In a variable texture field, the corrected BD model resulted in remarkable spatial similarity of BD between the corrected on-line and core sampling method. Therefore, it can be concluded that the BD model with the new M can be used for on-line measurement of soil compaction in loamy sand, sandy loam, loam, silt loam, and silt soils at different MC. bearing in mind that the difference in clay content is minimal (83-175 g kg(-1)). (C) 2008 Elsevier B.V. All rights reserved.