Field spatial and temporal patterns of soil water content and bulk density changes (original) (raw)
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Soil bulk density evaluation by conventional and nuclear methods
Australian Journal of Soil Research, 2005
Among the methods used to measure soil bulk density, the following have been prominent: paraffin sealed clod (PS), volumetric ring (VR), and the modern methods like gamma ray computed tomography (GCT) and the neutron/gamma surface gauge (SG). The objective of this work was to compare soil bulk density values obtained through these methods, with the aim of assisting researchers on the choice of the more appropriate method. For this, a 200 m spatial transect was chosen in an experimental area cultivated with coffee belonging to ESALQ/USP, Piracicaba, SP, Brazil. The SG readings were first taken in the field and thereafter soil samples were collected at 8 different points, spaced at 25 m, for the other methods. The lowest values of soil bulk density were obtained for the SG method (average 1.468 g/cm 3 ) and the highest for the PS (average 1.685 g/cm 3 ), which was similar to the GCT method (average 1.684 g/cm 3 ).
Botswana Journal of Technology, 2010
Characterisation of soil water, in particular water flow dynamics is fundamental in assessing the environmental implications to soil management. Soil water characterisation was assessed by measuring soil water content and soil water potential in a draining profile of sandy and loamy soils. Mercury manometers and Neutron probe meter were connected to a 1.2 m high metal-reinforced container filled with soil samples, to simultaneously measure soil water potential and volumetric water content, respectively. Soil water contents (SWC) were found to decrease monotonically with time, with a rapid decrease in the first 50 hrs of free drainage in both soils. Sandy soil was more prone to huge losses of water than loamy soil attributed to numerous large drainable pores in sandy soil. An appreciable difference of SWC in the upper layer (SWC= 0.22 cm 3 /cm 3) and the bottom layer (SWC= 0.35 cm 3 /cm 3), in the case of loamy soil was attributable to its poor drainage properties.
Geoderma, 2014
The soil elemental (oxides) composition variation of three Brazilian soils submitted to the application of wetting and drying (W-D) cycles was measured in order to evaluate the possible changes in the calculated soil mass attenuation coefficient (μ) as a function of the cycles. Measurements of μ by using radioactive sources of 241 Am and 137 Cs were also performed. Gamma-ray computed tomography (CT) was used as a tool to evaluate the impact of changes in μ induced by the cycles in determinations of soil bulk density (d s). The measured and calculated values of μ presented good agreement. Significant modifications were not observed in the total elemental composition of the soils after the application of W-D cycles. As a consequence only slight changes in μ were observed. However, the use of CT allowed concluding that even small changes in μ can cause some change in d s .
Soil porous system changes quantified by analyzing soil water retention curve modifications
Soil & Tillage Research, 2008
Soil water retention curves (SWRC) relate soil water pressure head (h) to soil water content (θ) and can also be used to find information regarding soil pore distribution. To analyze SWRCs in relation to pore size distribution (PSD), changes due to wetting and drying (W-D) cycles were studied in three different tropical soils (Geric Ferralsol, GF; Eutric Nitosol, EN;
Spatial and temporal patterns of soil water content in an agroecological production system
Scientia Agricola
Spatial and temporal patterns of soil water content (SWC) can not only improve the understanding of soil water processes but also the water management in the field. The spatial distribution of SWC depends on the spatial variability of soil attributes, vegetation and landscape features. The aim of this study was to evaluate: i) the spatial and temporal variability pattern in an agroecological system; ii) understand the factors affecting the spatial variations of SWC; iii) determine if wet and dry zones conserve their spatial position; iv) evaluate the possibility of using this information to reduce the number of SWC measurements. The experiment was carried out in an area of 2,502 m 2 , where a regular grid with spacing of 10 m was laid out. At each point, time domain reflectometer sensors were installed at depths of 0.05, 0.15, 0.30 m to monitor the SWC for 18 days in 2014 (Jan, Feb and Mar) and 9 days in 2014/2015 (Dec and Jan). The SWC, at the three soil depths, followed a similar and systematic pattern, being highest in the deepest layers, and exhibited temporal stability. The correlation between SWC and clay content varied both with the depth and the magnitude of SWC. During the wet season it is necessary to intensify the sampling density to estimate the SWC, while during the dry season the Spearman rank correlation remained high indicating the need for a small sampling effort only. The driest zones tend to conserve their spatial position more for a longer period than compared to wettest zones .
Spatial patterns and correlation of soil properties of a lowland soil
Journal of Soil Science and Environmental Management, 2012
Soil water content (θ θ θ θ), bulk density (ρ ρ ρ ρ b) and associated properties greatly influence important soil and plant processes. A field experiment was carried out in Mococa, São Paulo, Brazil, in a lowland area with the objectives firstly, to assess the spatial variability of selected soil propertiesθ θ θ θ, ρ ρ ρ ρ b, total porosity and microporosity using classical and geostatistical techniques and secondly, to find out how they are correlated. Results generally showed that at 0 to 20 cm depth, θ θ θ θ at saturation and 5 cm were negatively skewed but positively skewed at the rest of the remaining depth of testing. On the other hand, kurtosis values were not consistent but were positive in both the top and subsoil. This implies that in both depths, tested parameters were highly variable and were not normally distributed. In top soil, only water at 1000 cm pressure and bulk density had negative skewness and kurtosis values. The values for nugget, sill, % nugget or randomness degree, and range for ρ ρ ρ ρ b decreased with depth also showing lower structured range which probably signifies that there was no depositional material on this site. To conclude, firstly, the spatial variability of most properties was moderate and the majority of soil properties were well described using spherical or exponential mathematical models. Secondly, the distances at which variables were correlated in the top and in the subsoil showed minor differences. Thirdly, semi-variance analyses in top and sub soils showed that differences exist in the patterns of spatial variability, with the sub soils showing strongest spatial dependence.
Comparison of Water Storage Variations Inside a Soil Profile in Different Soil and Vegetation Types
1991
This paper discusses the point variabili ty of soil water in different soils and vegetation covers. The spatial variability of soil water is studied inside a homogeneous barley field and inside a fairly homogeneous pine forest in a sandy groundwater basin. Further, the accuracy of the neutron scattering method is discussed. The average error of the neutron probe was 0.7 volume per cent. The stability of the probe could be improved if the measurement time is increased to 1-2 minutes. The peak-to-peak variation in clay-silt re mained 60 per cent below that of layered sandy soil. The upper-layer variability reflected the total storage variability better in fine grained soils than in coarse sandy soils. The spatial variability in a homogeneous barley field was on the average 3.5 volume per cent, which makes 40 mm in storage value. The effect of vegetation cover is strong; dense grass field was able to evapotranspir ate more than twice as much water as cultivated barley. The water stor...
Soil spatial variability and the estimation of the irrigation water depth
Scientia Agricola, 2001
The effects of soil water spatial variability previous to irrigation and of the field capacity on the estimation of irrigation water depth are evaluated. The experiment consisted of a common bean (Phaseolus vulgaris L.) crop established on a Kandiudalfic Eutrudox of Piracicaba, SP, Brazil, irrigated by central pivot, in which soil water contents were evaluated with a depth neutron gauge, in a grid of 20x4 points with lag of 0.5 m. In a given situation, the 80 calculated irrigation water depths presented a coefficient of variation of 29.3%, with an average water value of 18 mm, maximum of 41mm and minimum of 9 mm. It is concluded that the only practical way of irrigation is the use of an average water depth, due to the inherent variability of the soil, and that the search for better field capacity values does not imply in better water depth estimates. Key words: irrigation water depth, field capacity, spatial variability VARIABILIDADE ESPACIAL DO SOLO E A ESTIMATIVA DA LÂMINA DE IRRIGAÇÃO RESUMO: A influência da variabilidade espacial da umidade do solo em uma situação pré-irrigação e da capacidade de campo é avaliada no cálculo da lâmina de irrigação. O experimento constou de cultura de feijão (Phaseolus vulgaris L.) estabelecida em um ARGISSOLO da região de Piracicaba, SP, irrigada por pivô central, tendo as medidas de umidade sido feitas com sonda de nêutrons, em uma malha de 20x4 pontos, espaçados de 0.5 m. Em determinada situação, os 80 valores de lâmina de irrigação calculados apresentaram um coeficiente de variação de 29.3%, para uma média de 18 mm, com valor mínimo de 9 mm e máximo de 41mm. É concluído que a única forma prática de irrigação é o uso de uma lâmina média devido à variabilidade inerente ao solo, e que a procura de melhores valores para a capacidade de campo não implica em melhores estimativas da lâmina de irrigação. Palavras-chave: lâmina de irrigação, capacidade de campo, variabilidade espacial