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Incorporation of Water Content in the Weibull Model for Soil Aggregate Strength

^a Dep. of Agroecology and Environment, Faculty of Agricultural Sciences, Aarhus Univ., Research Centre Foulum, P.O. Box 50, DK-8830 Tjele, Denmark
^b Dep. of Earth and Planetary Sciences, Univ. of Tennessee, 1412 Circle Dr., Knoxville, TN 37922-1410
^c Dep. of Agronomy, Univ. of Kentucky, Agricultural Science Bldg. North, Lexington, KY 40546-0091

View larger version (18K): [in this window] [in a new window]   Fig. 1. Relationship between characteristic rupture energy, , and the relative water content (w/w0) for (a) Bygholm I soil, (b) Bygholm II soil, and (c) Maury soil Block 2 aggregates. Lines correspond to the fitted power law relationships summarized in Table 2. PAC = compacted treatment; REF = reference treatment; MP-N1 = moldboard plowing and 0 kg N ha–1 yr–1 treatment; MP-N4 = moldboard plowing and 336 kg N ha–1 yr–1 treatment; NT-N1 = no-tillage and 0 kg N ha–1 yr–1 treatment; NT-N4 = no-tillage and 336 kg N ha–1 yr–1 treatment.

View larger version (14K): [in this window] [in a new window]   Fig. 2. Relationship between the spread of rupture energy Weibull parameter, ß, and the relative water content (w/w0) for (a) Bygholm I soil, (b) Bygholm II soil, and (c) Maury soil Block 2 aggregates. Line for MP-N4 corresponds to the significant linear relationship summarized in Table 3. PAC = compacted treatment; REF = reference treatment; MP-N1 = moldboard plowing and 0 kg N ha–1 yr–1 treatment; MP-N4 = moldboard plowing and 336 kg N ha–1 yr–1 treatment; NT-N1 = no-tillage and 0 kg N ha–1 yr–1 treatment; NT-N4 = no-tillage and 336 kg N ha–1 yr–1 treatment.

View larger version (23K): [in this window] [in a new window]   Fig. 3. Cumulative density functions for the cumulative probability density function P(E Ei) vs. specific rupture energy E before and after normalization of E to the air-dry state [E(w/w0)] for (a) and (b) 4- to 8-mm Bygholm I aggregates, and (c) and (d) 8- to 16-mm Bygholm II aggregates. PAC = compacted treatment, and REF = reference treatment.

View larger version (25K): [in this window] [in a new window]   Fig. 4. Cumulative density functions for the cumulative probability density function P(E Ei) vs. specific rupture energy E before and after normalization of E to the air-dry state [E(w/w0)] for Maury Block 2 data: (a) moldboard plowing and 0 kg N ha–1 yr–1 treatment (MP-N1), (b) moldboard plowing and 336 kg N ha–1 yr–1 treatment (MP-N4), (c) no-tillage and 0 kg N ha–1 yr–1 treatment (NT-N1), and (d) no-tillage and 336 kg N ha–1 yr–1 treatment (NT-N4).

View larger version (19K): [in this window] [in a new window]   Fig. 5. Relationship between the rupture energy–aggregate size scaling factor (D) and the relative water content (w/w0) for the Bygholm soils. The lines are best-fit linear regressions; the relationship for the Bygholm II soil was not significant. PAC = compacted, and REF = reference treatment.