Volumetric Moisture Research Articles

Wireless Sensor Networks for precision horticulture in Southern Spain

In recent years many applications have been proposed for Wireless Sensor Networks (WSN). One of these is precision agriculture, where WSN can play an important part in the handling and management of water resources for irrigation, in understanding the changes in the crops to assess the optimum point for harvesting, in estimating fertilizer requirements and to predict crop performance more accurately. This paper describes our experience during the introduction and deployment of an experimental sensor network at an ecological horticultural enterprise in the semiarid region of Murcia. It presents the topology of the deployed network using four types of nodes (Soil Mote, Environmental Mote, Water Mote and Gateway Mote), some of them connected to different sensors distributed in the field. These sensors can measure various soil characteristics such us temperature, volumetric moisture content and salinity. For each node, the overall architecture, hardware and software components are described. The system also includes a real-time monitoring application operating from a computer placed in the central offices of the farm. The testing of the system was done in two phases: the first in the laboratory, to validate the functional requirements of the developed devices, the networking solution and the mote's power management; the second on the farm, to asses the functional performance of the devices, such as range, robustness and flexibility. The system was successfully implemented on a crop of ecological cabbage ( Brassica oleracea). The result was a low cost, highly reliable and simple infrastructure for the collection of agronomical data over a distributed area in horticultural environments.

Estimating volumetric surface moisture content for cropped soils using a soil wetness index based on surface temperature and NDVI

Surface soil wetness determines moisture availability that controls the response and feedback mechanisms between land surface and atmospheric processes. A study was carried out to estimate volumetric surface soil moisture content ( θ v ) in cropped areas at field (<10 2 m) to landscape ( ≤10 3 m) scales. Triangular scatters from land surface temperature (LST) and normalized difference vegetation index (NDVI) space were utilized to obtain a soil wetness index (SWI), from which θ v was derived, with the combination of dry and wet edges using data from ASTER (Advanced Space borne Thermal Emission and Reflection Radiometer) for field scale and MODIS (MODerate resolution Imaging Spectroradiometer) AQUA for landscape scale studies. The root mean square error (RMSE) of field scale θ v estimates was higher (0.039 m 3 m −3) than that of the landscape scale (0.033 m 3 m −3). The narrow swath (∼60 km) of finer resolution sensors (e.g. ASTER) often fails to capture the surface heterogeneity required in the triangle method for deriving SWI and could be one of the main reasons leading to relatively high error in θ v estimates. At both the scales, the lowest error of θ v estimates was found to be restricted within the NDVI range of 0.35–0.65. A geostatistical technique was applied to assess the influence of sub-pixel heterogeneity as an additional source of error for cross-scale comparison of θ v estimates obtained from LST–NDVI scatters. The overall errors of θ v estimates from LST–NDVI space were comparable with other globally available test results. The comparison of landscape scale θ v from MODIS AQUA with large-area global estimates from a passive microwave sensor (e.g. AMSR-E) with longer microwave frequency (e.g. C-band) yielded 75% correlation and 0.027 m 3 m −3 root mean square deviation (RMSD) for fractional vegetation cover less than 0.5. The study recommends the synergistic use of shorter microwave frequency (e.g. L-band) and optical–thermal infrared bands as the best way of satellite based passive soil moisture sensing for vegetated surfaces.

Substrate Depth Influences Sedum Plant Community on a Green Roof

Because the waterproofing membrane beneath green roofs is estimated to last at least 45 years, long-term plant performance beyond initial establishment is critical. Plants that survive initially on a green roof may not exist in the long term because of variability in climate and other factors. This study evaluated the effect of green roof substrate depth on substrate moisture, plant stress as measured by chlorophyll fluorescence, and plant community development and survival of 12 Sedum species over 4 years in a midwestern U.S. climate during 4 years of growth. Plugs of 12 species of Sedum were planted on 8 June 2005 and evaluated biweekly for absolute cover (AC). Most species exhibited greater growth and coverage at a substrate depth of 7.0 cm and 10.0 cm relative to 4.0 cm. For the species evaluated, substrate depths of at least 7.0 cm are highly recommended. AC of Sedum was significantly greater at this substrate depth than at 4.0 cm. Mean volumetric moisture content of the three substrate depths followed the same pattern as AC. When averaged over time, the 4.0-cm substrate depth held less moisture than depths of 7.0 or 10.0 cm, whereas the 7.0- and 10.0-cm substrate depths were statistically the same. Species exhibiting the greatest AC at all substrate depths were S. floriferum, S. sexangulare, S. spurium ‘John Creech’, and S. stefco. In general, species that are less suitable at these substrate depths are S. ‘Angelina’, S. cauticola ‘Lidakense’, S. ewersii, S. ochroleucum, and S. reflexum ‘Blue Spruce’.

Experimental study of the influence of moisture and dry density on a silt soil using a monopole probe

AbstractABSTRACT: Dielectric measurements have been made on a silt soilboard with three moisture contents and different densities using a short monopole probe at microwave frequencies. A detailed analysis has been made to obtain the variation law of the real permittivity with the volumetric moisture content and the dry density of the soil studied. © 2009 Wiley Periodicals, Inc. Microwave Opt Technol Lett 51: 820–826, 2009; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.24185

Moisture controls on carbon dioxide dynamics of peat‐Sphagnum monoliths

AbstractSphagnum moss is the major peat‐forming vegetation component in boreal peatlands. The relationship between Sphagnum productivity and moss moisture content has been documented; however, the link between moss moisture content and conditions in the underlying peat column is less clear. We conducted a pilot study in which we monitored volumetric moisture content with depth and gravimetric water content of Sphagnum capitula and CO2 exchange for two peat monoliths with intact moss layer dominated by Sphagnum fuscum and S. magellanicum. Measurements were made under drying conditions and rewetting from below and following simulated precipitation events. Capitulum moisture content was related to water table position but varied between species. Both capitulum moisture content and water table position could be used to explain net CO2 exchange and respiration during drying and rewetting from below, although hysteresis was apparent where respiration was lower on rewetting than drying for the same water table position. Precipitation complicated these relationships because small events (&lt;5 mm) rewetted the upper few centimeters of moss resulting in a change in capitulum moisture content equivalent to a rise in water table position of ∼20 cm. This change in capitulum moisture content resulted in substantial shifts in both photosynthesis and respiration rates without affecting water table position or subsurface volumetric water contents as shallow as 5 cm below the surface. While these small events will be difficult to measure in the field, this study suggests they are essential to effectively track or model Sphagnum productivity because they may contribute significantly to seasonal carbon balance. Copyright © 2009 John Wiley &amp; Sons, Ltd.

Temperature Dependable Microwave Dielectric Model for Frozen Soils

In this paper, the temperature dependable dielectric model for moist soils was developed on the basis of the generalized refractive mixing dielectric model (GRMDM) recently proposed by Mironov etal. to provide for substantially less error, as compared to the most popular model by Dobson etal.. This model was substantiated with the use of the dielectric data measured by Curtis etal.. For a speciflc soil type, the temperature dependable GRMDM was shown to make as accurate predictions of this value, as a function of volumetric moisture, wave frequency, and temperature, as the dielectric data measurement accuracy is. The error of dielectric predictions was tested in the range of temperatures from 10 to 40 - C, frequencies from 300MHz to 26.5GHz, and moistures varying from those of dry soil to the ones corresponding to full soil water capacity. The Silty Sand soil tested contained 14, 9, and 77% of clay, silt and sand respectively. In addition, the error of dielectric predictions with the temperature dependable GRMDM was compared with that of Dobson's model, proving a lot more accurate predictions.

Automation of Pavement Sublayer Moisture Content Determination Using Long-Term Pavement Performance Time Domain Reflectometry Data and Micromechanics

Time domain reflectometry (TDR) is one of the reliable methods to measure in situ moisture content of unbound base and subgrade materials. However, the waveform data obtained from the TDR device do not provide in situ moisture content directly. Rather, the data must be analyzed to determine volumetric moisture content, which is the final product of TDR-related technology; that is, a TDR trace is analyzed to determine the value of the associated dielectric constant, which depends on the soil surrounding the TDR probe affecting the moisture content determination. However, because existing methods to determine the dielectric constant and moisture content are immersed in systematic errors, a new approach was developed; it used the transmission line equation and a three-phase micromechanics approach to improve the accuracy of the interpretation of TDR data for calculating the dielectric constant and the moisture content. Because the system identification method used to calculate parameters in the new approach was an iterative solution scheme, a computational program was required to provide rapid, accurate, and repeatable calculation of parameters. To address this need, a program was developed to facilitate the calculation of dielectric constant, dry density, and moisture content using the micromechanics approach. Details regarding the feature, algorithm, and results of the program are provided.

Ecohydrologically important subsurface structures in peatlands revealed by ground‐penetrating radar and complex conductivity surveys

The surface pattern of vegetation influences the composition and humification of peat laid down during the development of a bog, producing a subsurface hydrological structure that is expected to affect both the rate and pattern of water flow. Subsurface peat structures are routinely derived from the inspection of peat cores. However, logistical limits on the number of cores that can be collected means that the horizontal extent of these structures must be inferred. We consider whether subsurface patterns in peat physical properties can be mapped in detail over large areas with ground‐penetrating radar (GPR) and complex conductivity by comparing geophysical measurements with peat core data along a 36 m transect through different microhabitats at Caribou Bog, Maine. The geophysical methods show promise. Peat horizons produced radar reflections because of changes in the volumetric moisture content. Although these reflections could not be directly correlated with the peat core data, they were related to the depth‐averaged peat properties which varied markedly between the microhabitats. Well‐decomposed peat below a hollow was characterized by a discontinuous sequence of chaotic wavy reflections, while distinct layering of the peat below an area of hummocks coincided with a pattern of parallel planar reflections. The complex conductivity survey showed spatial variation in the real and imaginary conductivities which resulted from changes in the pore water conductivity; peat structures may also have influenced the spatial pattern in the complex conductivity. The GPR and complex conductivity surveys enabled the developmental history of the different microhabitats along the studied transect to be inferred.

In-situ characterization of soil moisture content using a monopole probe

In this paper, a microwave non-destructive experimental tool based on a monopole antenna is used for the determination of the complex permittivity of soils. The monopole mounted on a ground plane is buried in the soil, and its reflection coefficient measured at the feed point by a vector network analyzer (VNA) depends on the dielectric properties of the surrounding medium at a given frequency. In particular, this study is focused on the evaluation of the change of dielectric properties of different soils with the moisture content. In general, the dependence of the dielectric properties of a soil with the antenna reflection coefficient is nonlinear in nature, and the solution of the inverse problem requires a sophisticated algorithm. Thus, we have used two types of modeling, analytical (Wu's approach) and numerical (FDTD), to further understand the influence of fundamental parameters (antenna geometry and soil properties) on the frequency response of the antenna reflection coefficient. These models have allowed us to develop a novel inverse algorithm for the determination of the mean real permittivity based on the position of the antenna resonant frequencies in a wide frequency range. Moreover, a high resolution algorithm based on the Prony's approach has been developed in order to fit the complex reflection coefficient and determine afterwards the complex permittivity and the volumetric moisture content of a soil. Experimental results from different types of sands have been analyzed.

Observed evidence of subgrade moisture influence on pavement longitudinal profile

The relationship between subgrade moisture parameters and pavement profile was explored for 34 asphalt pavements of the seasonal monitoring program (SMP) in the long-term pavement performance (LTPP) program. Volumetric moisture content was quantified in terms of the moisture index (MI), representing moisture as reasonably related to subgrade performance. Using power spectral density (PSD), roughness was evaluated in 21 individual wavebands. From statistical analysis, it was concluded that subgrade moisture significantly affects roughness in the wavebands of 14.9 to 31.2 m and 24.0 to 31.2 m for nonfreezing sites, and in the waveband of 14.9 to 24.0 m for freezing sites. At nonfreezing sites, as the magnitude and variation of moisture increase, pavement surface profile deteriorates quickly. At freezing sites, it was found that moisture variation by freezing contributes to roughness deterioration. Moreover, it was found that pavement thickness and the percent passing the top 0.002 mm of subgrade are significant factors accelerating roughness progression at nonfreezing and freezing sites, respectively.

Influences of forest floor cleaning on the soil respiration and soil physical property of a larch plantation in Northeast China

Aimed to estimate how forest floor cleaning affected the carbon budget and soil physical feature, a 2-yr (2005–2006) measurement on soil respiration, soil bulk density, capillary porosity, soil temperature and soil volumetric moisture was carried out in a larch plantation. Firstly, forest floor cleaning evidently decreased soil respiration. Annual cumulative soil CO 2 efflux decreased from 44.2 μmol·m −2 a −1 to 22.4 μmol·m −2 a −1. Secondly, cleaning practice slightly increased soil temperature at the growing season, but reduced it at the dominant winter season. It also made soil moisture higher in summer, but lower in spring and autumn. Moreover, the cleaning practice induced more compact soil compared with the uncleaned control. Thirdly, forest floor cleaning of litters and understory shrubs could cause non-respiratory carbon loss of about 175.0 mol·m −2. This loss decreased from 175.0 mol·m −2 to 137.4 mol·m −2 when soil respiratory carbon loss decreased. However, the alteration of soil physical characters in the cleaned plots should be carefully considered since this alteration was not favorable to the growth of larch plantation in a long run.

Conservation agriculture as a sustainable option for the central Mexican highlands

Tropical highlands of the world are densely populated and intensively cropped. Agricultural sustainability problems resulting from soil erosion and fertility decline have arisen all over this agro-ecological zone. Based on selected soil quality indicators, i.e. time-to-pond, aggregate distribution and stability (expressed as the mean weight diameter (MWD) for dry and wet sieving, respectively) and soil moisture, from a representative long-term sustainability trial initiated in 1991 in Central Mexico (2240 masl; 19.31°N, 98.50°W; Cumulic Phaeozem), some insights into the feasibility of conservation agriculture (CA) as part of a sustainable production system in the tropical highlands are given. Zero tillage plots with crop residue removal showed low aggregate distribution (average MWD = 1.34 mm) and stability (average MWD = 0.99 mm) resulting in top layer slaking, increased erosion and low time-to-pond values. Retaining the residue in the field with zero tillage avoided the above-mentioned negative evolution for both aggregate distribution as stability (average MWD = 2.77 and 1.51 mm, respectively) and even improved the physical conditions of the soil as compared to conventional practice. Throughout the growing season the lowest soil moisture content was found in zero tillage without residue (average over the entire growing season = 20.5% volumetric moisture content), the highest in zero tillage with residue retention (average = 29.7%) while conventional tillage had intermediate soil moisture values (average = 27.4%). Zero tillage without residue retention had most days of soil moisture values under permanent wilting point, while zero tillage with residue retention had the least. Taking into account these results, zero tillage with residue retention can clearly be a part of an integrated watershed management scheme towards sustainable agriculture in the tropical highlands. It is clear that to develop new management practices to improve water use, reduce erosion and enhance human labor/animal power focus must be on the use of conservation agriculture both for rainfed as well as irrigated production systems and be fine tuned for each system.

Influence of environmental moisture on TRMM‐derived tropical cyclone precipitation over land and ocean

The rainfall climatology and persistence model (R‐CLIPER) used operationally in the Atlantic Ocean basin mainly utilizes tropical cyclone (TC) intensity to predict TC rainfall. However, the rain production by TCs is also influenced by environmental parameters such as total moisture availability, horizontal moisture convergence, vertical wind shear, and sea surface temperature (SST). Previous TC case studies have used environmental moisture parameters to diagnose TC rainfall. In this study, we composite over 3000 snapshots of 3‐hourly TRMM 3B42 rainfall fields for Atlantic landfalling tropical cyclones between 1998–2006 to analyze the rainfall distribution and storm total volumetric rain as a function of total precipitable water (TPW), horizontal moisture convergence (HMC), and ocean surface flux (OSF) over land and over ocean. For over ocean conditions, higher TPW, HMC, or OSF values are associated with higher azimuthally averaged rain rates. Over land, this is still the case but less obvious. Computing the linear correlation coefficients between total volumetric rain and moisture parameters shows this fact much more clearly. These coefficients are generally higher for over ocean conditions than those for over land conditions. To test if moisture parameters can provide additional information other than TC intensity to help TC rainfall forecasts, a multiple linear regression is performed between TC volumetric rain and several variables including TC maximum wind speed, TPW, HMC, and OSF. By adding moisture parameters as additional variables, TC volumetric rain will be better predicted than using TC intensity (maximum wind speed) only. The correlation coefficient between volumetric rain and maximum wind speed can increase from 0.52 (0.51) to 0.67 (0.65) for over ocean (land) conditions by adding TPW, HMC and OSF. By adding TPW only, the correlation coefficient increases to 0.59 and 0.64 for over ocean and land, respectively.

Modeling soil moisture effects on net nitrogen mineralization in loamy wetland soils

Nutrient dynamics in wetland ecosystems are largely controlled by soil moisture content. Therefore, the influence of soil moisture content on N mineralization should be explicitly taken into account in hydro-ecological models. The aim of this research was to establish relationships between N mineralization and soil moisture content in loamy to silty textured soils of floodplain wetlands in central Belgium. Large undisturbed soil cores were taken, incubated for 3 months under various moisture contents, and zero order and first order N mineralization rates were calculated. We used the percentage water-filled pore space (WFPS) as an expression of soil moisture because it is a better index for aeration dependent biological processes than volumetric moisture content or water retention. The relationship between the N mineralization rate and %WFPS was described by a Gaussian model. The optimum WFPS for N mineralization ranged between 57% and 78%, with a mean of 65% ± 6% WFPS. Expected annual net N mineralization rates at field temperature (9.7°C) and at optimal moisture content varied between 30 and 186 kg N ha-1 (0–15 cm depth) year-1, with a mean of 110 ± 42 kg N ha-1 (0–15 cm) year-1. The mean N turnover rate amounted to 2.3 ± 1.1 g N 100 g-1 N year-1. Multiple linear regressions between N mineralization and general soil parameters showed that soil structure has an overriding impact on N mineralization in wetland ecosystems.

The penetration and measurement of GPR microwave on reclaimed soil moisture under constrained condition

Ground penetrating radar (GPR) is a geophysical method that incorporates a microwave technique, which can gather a great deal of information about the near-surface in a non-destructive penetration way. The aim of this study is to investigate the application of GPR under the constrained conditions of reclaimed soil. There is a large difference between the result of volumetric moisture content (VMC) detected by GPR and the one measured by the oven drying method (ODM). However, the two methods give similar results when VMC reaches about 40%, beyond this moisture level, the difference in the results obtained using the two methods increases with the increase of moisture content. The VMC of reclaimed soil detected by GPR shows a close correlation with soil electrical conductivity and soil porosity. Consequently, a mathematical model of VMC for reclaimed soil has been developed. This correlation provides a real-time soil moisture data on a field scale, and solves the problem posed by the use of the kernel technique for efficient irrigation management.

Comparing Spectral Soil Inference Systems and Mid‐Infrared Spectroscopic Predictions of Soil Moisture Retention

Mid‐infrared spectroscopy has been proposed as a cheap yet accurate alternative to a number of laboratory methods for measuring soil properties. While accurate predictions of a number of basic soil constituents have been reported, properties associated with soil structure have received far less attention. In this study, we looked at the efficacy of mid‐infrared reflectance spectroscopy in predicting moisture retention and whether better predictions can be achieved using pedotransfer functions using spectroscopic predictions of basic soil constituents as inputs. Three methods were used to predict volumetric moisture retention: (i) mid‐infrared (MIR) spectra and partial least squares regression, (ii) a neural network pedotransfer function (PTF) using laboratory particle‐size distribution and bulk density data, and (iii) a pedotransfer function with MIR‐predicted particle‐size distribution and bulk density as inputs. We used Lin's concordance correlation coefficient as a goodness‐of‐fit measure. Predictions of volumetric moisture retention on intact structured soils were generally poor, particularly at the wet end. Improved predictions were observed at dry‐end matric potentials, where moisture retention was more correlated with particle‐size distribution than soil structure. The neural network PTF was found to have better goodness of fit for all matric potentials; however, predictions at larger matric potentials (wet end) were still poor due to poor bulk density predictions. In light of this work, we propose that while MIR spectroscopy may be a valuable predictor of fundamental soil constituents such as particle‐size fractions and organic C, predictions of soil properties dependant on soil structure, such as volumetric moisture retention, may prove difficult. Mid‐infrared spectroscopy in combination with PTFs should provide improvements to moisture retention predictions through improved representation of the influential processes, namely soil structure and adsorptive forces.

Irrigation scheduling and irrigation systems: optimising irrigation efficiency for container ornamental shrubs

Water use and plant growth and quality were compared across different nursery stock beds, different methods of applying irrigation, and different methods of scheduling irrigation. With overhead irrigation, scheduling of irrigation according to plant demand, along with an irrigation system designed to maximise irrigation uniformity, resulted in substantial water savings, without reducing plant quality. This was the case in both wet and dry years. In the dry year, plant quality was particularly good when grown on a sub-irrigated sand bed; this system also used less water than any of the overhead irrigation systems. Two different systems were effective in scheduling overhead irrigation, one based on the volumetric moisture in the growing substrate, and the other based on plant evapotranspiration. The latter was determined with a small sensor with wet and dry artificial “leaves”, the output of which correlated with that obtained following the Penman–Monteith method based on a full set of meteorological data.

Matric Potential Measurements by Polymer Tensiometers in Cropped Lysimeters under Water‐Stressed Conditions

In many regions of the world, plant growth and productivity are limited by water deficits. As a result of more frequent and intense droughts, the area of land characterized as very dry has more than doubled since the 1970s. Consequently, understanding root water uptake under water‐stressed conditions is gaining importance. The performance of a recently developed polymer tensiometer (POT) designed to measure matric potentials down to −1.6 MPa was evaluated and compared with volumetric moisture content measurements in dry soil. Three irrigation intensities created severe, intermediate, and no water stress conditions in lysimeters with growing maize (Zea mays L.) plants. By monitoring matric potentials using POTs, levels of local water stress in our experiments were better defined. When the defined stress levels were reached, volumetric moisture measurements for this particular loam soil were below 0.1, thus less informative compared with matric potential measurements. The observed matric potential profiles indicate significant root water uptake between 0.3‐ and 0.5‐m depth in the later growth stages under water‐stressed conditions. The temporal pattern of matric potential profiles reflected changing root water uptake behavior under dry conditions. As the total soil water potential is a direct indication of the amount of energy required by plants to take up water, POTs may contribute to quantifying root water uptake in dry soils.

EVALUATION OF A COMBINED SOIL EC AND MOISTURE SENSOR AND ITS USE TO CO-MANAGE SOIL MOISTURE AND VINE NITROGEN IN GRAPEVINES (CV. SHIRAZ) UNDER DEFICIT IRRIGATION

ISHS V International Symposium on Irrigation of Horticultural Crops EVALUATION OF A COMBINED SOIL EC AND MOISTURE SENSOR AND ITS USE TO CO-MANAGE SOIL MOISTURE AND VINE NITROGEN IN GRAPEVINES (CV. SHIRAZ) UNDER DEFICIT IRRIGATION

Temperature dependence of dielectric properties of moist soils

Heating of soil using microwaves has several applications in geosciences, including soil remediation, neutralization of land mines, and microwave-enhanced thermography. Numerical simulation of microwave-induced soil heating processes requires knowledge of the electrical properties of the soil as a function of temperature, moisture content, and frequency of the electromagnetic wave. This paper describes a semi-empirical model for calculating the dielectric properties of moist soils at various moisture contents, temperatures, and frequencies (within the band of 1–10 GHz). The proposed model is an extension of the generalized refractive mixing dielectric model (GRMDM) for moist soils. Predictions of the proposed model were found to be in good agreement with experimental data reported in the literature. Results of a parametric study suggest that the temperature dependency of the dielectric properties of moist sand is more pronounced for higher volumetric moisture contents.