 |
| Titel |
A preliminary study of multifractality from microprofiles of soil penetration resistance |
| VerfasserIn |
Jorge Paz-Ferreiro, Jose Garcia Vivas Miranda, Laura F. S. da Silva, Edson Eiji Matsura, Mara de Andrade Marinho |
| Konferenz |
EGU General Assembly 2011
|
| Medientyp |
Artikel
|
| Sprache |
Englisch
|
| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 13 (2011) |
| Datensatznummer |
250047416
|
|
|
|
|
|
| Zusammenfassung |
| Soil strength is an important characteristic affecting many aspects of agricultural soils, such
as the performance of cultivation implements, root growth, trafficability features, etc. The soil
strength results from cohesive forces between soil particles and their frictional resistance.
Characterization of soil strength is usually made by measuring the resistance to
penetration (RP) of a metallic plunger with a particular shape, usually a cone. Field
penetrometers have been widely used for estimating resistance to root growth in soil,
because soil RP is roughly indicative of the pressure required for soil penetration
by roots. However, plant growth is not only affected by RP, but also by soil water
content and soil aeration. The least limiting water range (LLWR) is an index of
structural quality for plant growth, which takes into account those three soil physical
properties. LLWR was defined as “the range in soil water content within which
limitations to plant growth imposed by water potential, aeration and mechanical
impedance are minimal”. For LLWR assessment, RP is currently recorded in laboratory
conditions using micropenetrometers. The objective of this study was to explore the
effect of soil bulk density on soil PR microprofiles using multifractal analysis. The
studied soil was a Rhodic Hapludox (Latossolo Vermelho Distroférrico típico in the
Brazilian Soil Classification System) sampled in Campinas, SP, Brazil. Remolded soil
core samples were prepared using air-dried fine earth (< 2.0 mm), obtained from
disturbed soil samples, repacked in volumetric steel rings (5 cm diameter, 5 cm
length).The remolded soil core samples were built applying seven levels of bulk density,
i.e., 1000, 1100, 1200, 1300, 1400, 1500 and 1600 kg m-3. After saturation with
water, samples were put in a pressure plate extractor under a pressure of 750 kPa.
At equilibrium, when the outflow has ceased, the soil RP was measured using a
computer-controlled penetrometer having a cone with a semi-angle of 30º, a base area of
0.1256 cm2(about 4 mm diameter), and a penetration speed of 1 cm min-1. For
each bulk density value, three replicated cores were studied and three microprofiles
per core were recorded. Multifractal analysis of each experimentally obtained RP
microprofile was performed using the box-counting based moment method. PR profiles
were partitioned into subsequently smaller segments, following a multiplicative
cascade procedure and they were normalized in order to have a probability mass
function. Next, partition functions have been calculated for all the study data sets. Plots
of the normalized measure versus measurement scale for moments q = 10 to q =
-10 obeyed power low scaling, showing linear behaviour over 8 regression data
points. Moreover, PR microprofiles behave like a multifractal system. At the imposed
soil water potential, multifractal parameters extracted from the central part of the
generalized dimension and the singularity spectra were not significantly affected by bulk
density. In contrast, width of the left part of the singularity spectra showed a trend to
decease as the bulk density increased, so that parameters derived from this portion
of the spectra best discriminate between RP for successive bulk density values.
Consequences of RP multifractal behaviour for LLRW assessment are outlined. |
|
|
|
|
|
|