Fig. 1. The experimental design at Kuru. On the right 20 m sample plot divided to four subplots with penetration resistance and rut depth measurement points (●) and soil sample plots (○).
| Table 1. Soil characteristics at the study plots. VWC = Volumetric water content (%) at 0–10 cm, 10–20 cm depth in mineral soil, PR = Penetration resistance (Mpa) at 20 cm, 10–40 cm depth, BD = Soil bulk density (g cm–3) at 0–10 cm, 10–20 cm depth in mineral soil, ARP = Average steel rod penetration (cm), Org. layer = Depth of organic layer (cm), Soil type (EN ISO 2002, 2004): Sandy Silt (1); Silty sand (2). | |||||||||
| Plot | VWC 0–10 Mean (std.dev.) % | VWC 10–20 Mean (std.dev.) % | PR 20 Mean (std.dev.) MPa | PR 10–40 Mean (std.dev.) MPa | BD 0–10 Mean (std.dev.) g cm–3 | BD 10–20 Mean (std.dev.) g cm–3 | ARP Mean (std.dev) cm | Org. layer Mean (std.dev.) cm | Soil type |
| 11 | 39.62 (3.84) | 26.58 (7.18) | 1.63 (1.43) | 1.80 (0.83) | 1.35 (0.10) | 1,32 (0.20) | 64.47 (24.01) | 10.45 (1.84) | 2 |
| 12 | 31.31 (2.34) | 33.93 (3.50) | 1.46 (0.97) | 1.55 (0.54) | 1.12 (0.14) | 1.24 (0.06) | 55.80 (14.83) | 9.60 (1.27) | 2 |
| 13 | 32.77 (2.32) | 37.93 (3.65) | 1.37 (0.88) | 1.38 (0.49) | 1.17 (0.08) | 1.26 (0.04) | 66.32 (6.57) | 10.82 (0.95) | 2/1 |
| 14 | 64.35 (-) | 46.12 (-) | 1.02 (1.04) | 1.35 (0.43) | 0.73 (-) | 1.27 (-) | 54.00 (-) | 12.00 (-) | 2 |
| All | 35.41 (7.14) | 33.93 (6.96) | 1.45 (1.11) | 1.56 (0.64) | 1.19 (0.17) | 1.27 (0.12) | 61.82 (17.05) | 10.33 (1.50) | |
| 21 | 39.18 (4.26) | 34.38 (3.54) | 1.38 (1.19) | 1.56 (0.84) | 1.29 (0.18) | 1.43 (0.14) | 49.59 (4.88) | 13.06 (1.51) | 2 |
| 22 | 25.26 (3.55) | 28.62 (2.40) | 1.85 (1.13) | 1.75 (0.76) | 1.17 (0.11) | 1.36 (0.06) | 55.30 (2.46) | 9.90 (0.74) | 2/1 |
| 23 | 29.28 (1.66) | 32.38 (3.51) | 1.41 (0.66) | 1.38 (0.44) | 1.00 (0.12) | 1.22 (0.10) | 51.61 (1.54) | 7.42 (0.79) | 2 |
| 24 | 41.88 (-) | 36,48 (-) | 0.88 (1.00) | 1.51 (0.85) | 0.95 (-) | 1.58 (-) | 24.00 (-) | 10.00 (-) | 2 |
| All | 31.34 (6.92) | 31.59 (4.07) | 1.50 (1.04) | 1.56 (0.72) | 1.14 (0.18) | 1.34 (0.14) | 51.10 (6.98) | 10.06 (2.43) | |
| All | 33.47 (7.28) | 32.65 (5.93) | 1.48 (1.07) | 1.56 (0.68) | 1.17 (0.18) | 1.31 (0.14) | 56.57 (14.17) | 10.20 (2.01) | |
Fig. 2. Particle size distributions of study plots.
Fig. 3. Penetration resistance profiles of study plots before harvesting.
Fig. 4. Relationships between volumetric water content (VWC, %) at 0–10 cm depth in mineral soil, penetration resistance before harvesting (PR, MPa), average at the depth of 20 cm and bulk density (BD, g cm-3) at 0–10 cm depth in mineral soil.
Fig. 5. The average rut depths of the study plots.
| Table 2. Pearson correlation coefficients between rut depths (after one harvester pass and three forwarder passes) and soil properties calculated as averages for the test tracks. VWC = volumetric water content (%) 0–10/10–20 cm depth, BD = soil bulk density (g cm-3) 0–10/10–20 cm depth, PR = penetration resistance (MPa) 0–20/5–40 cm depth, Org. layer = depth of organic layer (cm), Stonin. = average rod penetration (cm), Volume = Stand volume before harvesting (m3 ha-1), Harv. rut = rut depth after harvester pass (cm), Rut = rut depth after three forwarder passes (cm). | ||||||||||||
| VWC 0–10 | VWC 10–20 | BD 0–10 | BD 10–20 | PR 0–20 | PR 5–40 | Org. layer | Stonin. | Volume | Harv. rut | Rut | ||
| VWC 0–10 | Pearson Correlation | 1 | .003 | .297** | .219* | –.294** | –.081 | .416** | .082 | .287** | .269** | .445** |
| Sig. (2-tailed) | .974 | .001 | .020 | .002 | .395 | .000 | .389 | .002 | .004 | .000 | ||
| VWC 10–20 | Pearson Correlation | 1 | –.115 | –.091 | –.132 | –.198* | .216* | –.018 | .094 | –.070 | –.049 | |
| Sig. (2-tailed) | .227 | .335 | .165 | .036 | .022 | .848 | .320 | .463 | .610 | |||
| BD 0–10 | Pearson Correlation | 1 | .246** | .009 | .202* | .542** | .130 | .259** | –.009 | .058 | ||
| Sig. (2-tailed) | .009 | .923 | .032 | .000 | .171 | .006 | .921 | .542 | ||||
| BD 10–20 | Pearson Correlation | 1 | –.049 | .070 | .641** | –.493** | .206* | .096 | .195* | |||
| Sig. (2-tailed) | .609 | .462 | .000 | .000 | .029 | .310 | .038 | |||||
| PR 0–20 | Pearson Correlation | 1 | .785** | –.110 | –.087 | –.075 | –.240* | –.296** | ||||
| Sig. (2-tailed) | .000 | .248 | .359 | .427 | .010 | .001 | ||||||
| PR 5–40 | Pearson Correlation | 1 | .050 | –.048 | .026 | –.310** | –.307** | |||||
| Sig. (2-tailed) | .598 | .614 | .785 | .001 | .001 | |||||||
| Org. layer | Pearson Correlation | 1 | .007 | .493** | .165 | .276** | ||||||
| Sig. (2-tailed) | .941 | .000 | .081 | .003 | ||||||||
| Stonin. | Pearson Correlation | 1 | .019 | .186* | .146 | |||||||
| Sig. (2-tailed) | .843 | .049 | .122 | |||||||||
| Volume | Pearson Correlation | 1 | .100 | .207* | ||||||||
| Sig. (2-tailed) | .293 | .027 | ||||||||||
| Harv. rut | Pearson Correlation | 1 | .787** | |||||||||
| Sig. (2-tailed) | .000 | |||||||||||
| Rut | Pearson Correlation | 1 | ||||||||||
| Sig. (2-tailed) | ||||||||||||
| ** = Correlation is significant at the 0.01 level (2-tailed). | ||||||||||||
| * = Correlation is significant at the 0.05 level (2-tailed). | ||||||||||||
| Table 3. Mixed-linear models predicting the logarithm of the average rut depth (cm) in a measurement point. CM = Cumulative mass driven over measurement point (kg), VWC = Volumetric water content (%) at 0–10 cm depth in mineral soil, PR = Penetration resistance (MPa) at 5–40 cm depth, OL = organic layer depth (cm), Hr = harvester rut depth (cm), σ2plot = variance for the plot, σ2meas = variance for successive measurements, ρplot and ρmeas correlation coefficients for measurement points within plot and for successive measurements. AIC = Akaike´s Information Criterion. | ||||||||||
| Model Parameter | 1 Estimate (SE) | Sig. | 2 Estimate (SE) | Sig. | 3 Estimate (SE) | Sig. | 4 Estimate (SE) | Sig. | 5 Estimate (SE) | Sig. |
| Fixed | ||||||||||
| Intercept | 1.1785 (0.200) | 0.000 | 0.028 (0.337) | 0.935 | –0.168 (0.148) | 0.704 | 0.312 (0.483) | 0.522 | 0.313 (0.097) | 0.002 |
| CM | 0.0000084 (0.0000004) | 0.000 | 0.0000084 (0.000) | 0.000 | 0.0000084 (0.0000004) | 0.000 | 0.0000084 (0.0000004) | 0.000 | 0.0000065 (0.000) | 0.000 |
| PR | –0.375 (0.121) | 0.002 | –0.375 (0.120) | 0.002 | ||||||
| VWC | 0.018 (0.009) | 0.067 | ||||||||
| OL, cm | 0.079 (0.042) | 0.066 | 0.084 (0.043) | 0.059 | ||||||
| Hr | 0.190 (0.017) | 0.000 | ||||||||
| Random | ||||||||||
| σ2plot | 0.631 (0.105) | 0.000 | 0.647 (0.106) | 0.000 | 0.652 (0.105) | 0.000 | 0.610 (0.103) | 0.000 | 0.349 (0.054) | 0.000 |
| ρplot | 0.173 (0.126) | 0.170 | 0.035 (0.122) | 0.776 | 0.060 (0.121) | 0.619 | 0.157 (0.127) | 0.216 | 0.138 (0.114) | 0.223 |
| σ2meas | 0.319 (0.043) | 0.000 | 0.320 (0.043) | 0.000 | 0.317 (0.042) | 0.000 | 0.319 (0.043) | 0.000 | 0.177 (0.017) | 0.000 |
| ρmeas | 0.531 (0.067) | 0.000 | 0.531 (0.067) | 0.000 | 0.526 (0.121) | 0.000 | 0.529 (0.067) | 0.000 | 0.213 (0.083) | 0.010 |
| AIC | 1255.8 | 1266.1 | 1263.0 | 1256.5 | 911.8 | |||||
Fig. 6. The influence of volumetric water content (%) at 0–10 cm depth in mineral soil on rut formation estimated with model 2 in Table 3.
Fig. 7. The allowed total overpassed mass keeping final rut depth under 10 cm as a function of harvester rut depth (model 5 of Table 3).
Fig. 8. Penetration resistance (PR, MPa) at the depth of 10–40 cm, after consecutive machine passes. Measurements are adjusted for rut depths.
Fig. 9. Average penetration resistance (PR, MPa) of 6 subplots after consecutive machine passes at soil depths of 20, 30 and 40 cm. Measurements are adjusted for rut depths.
Fig. 10. Penetration resistance profiles before and after harvesting. Measurements after harvesting are adjusted for average rut depth.
Fig. 11. Relationships between volumetric water content VWC (%) at 0–10 cm depth in mineral soil before harvesting, rut depth and penetration resistance PR (MPa) at the depth of 30 cm (adjusted for rut depth) after 6 machine passes.
| Table 4. Mixed-linear models predicting the logarithm of the average PR (MPa) at the depth of 10–40 cm in a measurement point. CM = Cumulative mass driven over measurement point (kg), VWC = Volumetric water content (%) at 10–20 cm depth in mineral soil, BD = soil bulk density (g cm–3) at 10–20 cm depth in mineral soil, Rdepth = rut depth (cm), σ2p = variance for the plot, σ2pm = variance for the measurement point, σ2meas and ρmeas variance and correlation coefficients for successive measurements. AIC = Akaike´s Information Criterion. | ||||||||
| Model Parameter | 1 Estimate (SE) | Sig. | 2 Estimate (SE) | Sig. | 3 Estimate (SE) | Sig. | 4 Estimate (SE) | Sig. |
| Fixed | ||||||||
| Intercept | 3.601 (0.879) | 0.022 | 3.539 (0.482) | 0.000 | 3.094 (0.629) | 0.012 | 2.997 (0.392) | 0.000 |
| CM | 0.00000131 (0.0000004) | 0.002 | 0.00000130 (0.0000004) | 0.002 | 0.00000291 (0.0000006) | 0.000 | 0.00000312 (0.0000006) | 0.0000 |
| VWC | –0.042 (0.016) | 0.075 | –0.042 (0.009) | 0.000 | –0.036 (0.012) | 0.047 | –0.035 (0.007) | 0.000 |
| BD | –1.324 (0.436) | 0.050 | –1.288 (0.242) | 0.000 | –1,064 (0.313) | 0.034 | –1.012 (0.197) | 0.000 |
| Rdepth | –0.033 (0.008) | 0.000 | –0.038 (0.008) | 0.000 | ||||
| Random | ||||||||
| σ2p | 0.025 (0.024) | 0.302 | 0.011 (0.012) | 0.369 | ||||
| σ2pm | 0.006 (0.008) | 0.490 | 0.021 (0.012) | 0.087 | 0.000 (0.007) | 0.958 | 0.006 (0.008) | 0.482 |
| σ2meas | 0.118 (0.014) | 0.000 | 0.119 (0.014) | 0.000 | 0.115 (0.013) | 0.000 | 0.116 (0.013) | 0.000 |
| ρmeas | 0.096 (0.0099) | 0.333 | 0.109 (0.101) | 0.278 | 0.080 (0.096) | 0.406 | 0.086 (0.097) | 0.371 |
| AIC | 205.6 | 210.8 | 199.2 | 200.6 | ||||