Figures (3)  Tables (2)

    • Figure 1. 

      Relationship between soil particle density (Dp, Mg·m−3) and soil organic matter content (SOM, kg·kg−1) for (a) calibration and (b) validation datasets. Horizontal and vertical bars indicate ± one standard deviation. Scatter plot of Dp vs SOM content for the (a) calibration dataset and (b) validation dataset.

    • Figure 2. 

      Relationship between soil particle density (Dp, Mg·m−3) and soil organic matter content (SOM, kg·kg−1) for the calibration dataset (n = 124). The regression line represents the best fit derived using simple linear regression with Eq. (5).

    • Figure 3. 

      Comparison of predicted and measured soil particle density (Dp, Mg·m−3) for the validation dataset using three prediction models: (a) McBride[8]; (b) Schjønning[9]; and (c) the current model. The 1:1 reference line indicates perfect agreement between predicted and measured values. Model performance was evaluated using the coefficient of determination (R2), root mean square error (RMSE), and mean error (ME).

    • SOMa (kg·kg−1) Dpb (Mg·m−3)
      Calibration
      data set
      (n = 124)      		 Validation data
      set (n = 55)      		 Calibration data
      set (n = 124)      		 Validation data
      set (n = 55)
      Mean 0.0386 0.0533 2.581 2.557
      Median 0.0367 0.0481 2.575 2.565
      Minimum 0.0004 0.0316 2.499 2.370
      Maximum 0.0759 0.1345 2.675 2.645
      a SOM was determined using the loss-on-ignition method as outlined in ASTM F1647-11. b Dp was determined following the ASTM D5550-14 standard test method for specific gravity of soil solids by gas pycnometer.

      Table 1. 

      Soil organic matter content (SOM) and particle density (Dp) of calibration and validation data sets.

    • Equation Eq. No. RMSE ME
      Dp = 2.646 − 2.8 × SOM (1) McBride et al.[8] 0.0632 −0.0602
      Dp = 2.686 − 2.649 × SOM (2) Schjønning et al.[9] 0.0213 −0.0121
      Dp = 2.6736 − 2.4131 × SOM (5) Current model 0.0194 −0.0119

      Table 2. 

      Root mean square error (RMSE) and mean error (ME) for Dp (Mg·m−3) predictions for 55 samples from the validation data set using the McBride (Eq. [1]), Schjønning (Eq. [2]), and the current model (Eq. [5]).