Simultaneous Measurement of Soil Penetration Resistance and Water Content with a Combined Penetrometer-TDR Moisture Probe

Abstract

and nutrient exploration have been obtained (Stelluti et al., 1998), and cone penetrometers have been used Soil mechanical impedance affects root growth and water flow, extensively in soil science studies to identify natural and controls nutrient and contaminant transport below the rooting and induced compacted layers (Henderson, 1989) or to zone. Among the soil parameters affecting soil strength, soil water content and bulk density are the most significant. However, field predict related soil properties (Ayers and Bowen, 1987). water content changes both spatially and temporally, limiting the Among the soil parameters that affect PR, soil water application of cone penetrometers as an indicator of soil strength. content and bulk density are the most significant (Vaz-Considering the presence of large water content variations within a quez et al., 1991). For example, Stitt et al. (1982) consoil profile and across a field and the large influence of water content ducted a comprehensive study of factors affecting PR on soil strength, there is need for a combined penetrometer-moisture in coarse-textured soils in the Atlantic Coastal Plain, probe to provide simultaneous field water content and soil resistance and used stepwise regression to relate mechanical immeasurements. Such a probe was developed, which uses the time pedance to various measured soil properties. The highdomain reflectometry (TDR) technique to determine water content est correlation coefficients were found for a regression and its influence on soil penetration resistance. The coiled TDR moismodel that included soil water content, soil particle ture probe consists of two parallel copper wires, each 0.8 mm in roughness and bulk soil density. Shaw et al. (1942) condiameter and 30 cm long, coiled around a 5-cm-long polyvinyl chloride (PVC) core with a 3-mm separation between wires. Calibration curves cluded that soil moisture is the dominant factor influencrelating the soil bulk dielectric constant measured by the coiled probe ing the force required to push a penetrometer into the to water content were obtained in the laboratory for a Columbia soil, with PR increasing as the moisture content define sand loam (coarse-loamy, mixed, superactive, nonacid, thermic creased. In an experimental study by Henderson et al. Oxyaquic Xerofluvent), a Yolo silt clay loam (fine-silty, mixed, non-(1988) it was found that PR was only slightly affected acid, thermic Typic Xerorthent), and washed sand, and data were with a decrease of soil water content to ≈70% of field analyzed based on a mixing model approach. Subsequently, field excapacity. However, the PR increased exponentially with periments were conducted to measure simultaneously the penetration a further reduction of the water content of the sandy soil. resistance (PR) and water content along a soil profile. Results showed This study showed that PR increased with an increase of a detailed water content profile with excellent correlation with the bulk density across the whole measured water content gravimetric method...

Modelling of soil penetration resistance for an oxisol under no-tillage

“…Most commonly, this property is evaluated using an impact penetrometer which works on the principle of soil penetration resistance (Pr) with a vertical impact representing a force (f) on a rigid rod that drives a cone of specific size into the soil (Vaz & Hopmans, 2001). the importance of determining Pr is the correlation with the effect of heavy machinery passing over the soil, affecting root growth and the soil physical properties, and is a way of rapidly obtaining results.…”

Sonda espiral de TDR para a medida da umidade no perfil do solo

“…Diversos tipos de sondas de TDR têm sido desenvolvidos e utilizados, como as sondas coaxiais (Topp et al, 1980), de duas, três e quatro hastes (Zegelin & White, 1989), espirais (Nissen et al, 1999;Vaz & Hopmans, 2001), segmentadas (Frueh & Hopmans, 1997) e outras (Inoue et al, 2001;Selker et al, 1993;Nissen et al, 1999). A configuração espiral proposta por Vaz & Hopmans (2001) é particularmente interessante, pois possibilita a construção de minissondas, com comprimento de poucos centímetros.…”

Minipenetrômetro dinâmico para determinação da resistência à penetração em amostras de solo indeformadas

“…A utilização desses equipamentos em condições de campo tem sido recomendada (Stolf, 1991;Stolf et al, 1998;Vaz et al, 2001). Nos penetrômetros dinâmicos, a penetração é proporcionada pelo impacto de um corpo metálico que cai de uma altura constante, o que o torna independente da força física do operador e dispensa mecanismos eletrônicos sofisticados.…”

“…O equipamento apresentado é uma miniatura baseada em equipamentos já descritos na literatura (Stolf, 1991;Vaz et al, 2001), e apresenta o mesmo princípio de funcionamento. O custo do material para sua construção, exceto o suporte auxiliar e a mão-de-obra, foi de cerca de U$ 10,00.…”