To investigate potential pollution of silage production to environment, we developed a multi-sensor-based instrument for tracking of carbon dioxide (CO2) and ethanol (EtOH) emissions from feed-out silage, incorporated real-time monitor of oxygen (O-2) concentration to distinguish different metabolic sources, and combined measurements of silage temperature (T-si)and pH to identify aerobic-stability and microbial-activity. Two common silage materials (maize and ryegrass), as experimental mini-silos treated either with or without a commercial bio-additive, were fermented in 1.5-L glass jars. The test, started immediately exposing samples to air, lasted 320 h (maize) or 600 h (ryegrass). The achieved data demonstrate: (i) all samples underwent from aerobic-stable to unstable processes; (ii) the initial emissions of CO2 and EtOH (0 similar to 10 h of aerobic-stable period) yielded mainly from anaerobic metabolism (maize, CO2: 1.104 1.294, EtOH: (0.570 0.807) & times; 10(-2); ryegrass, CO2: 0.805 0.888, EtOH: (0.060 0.408) & times; 10(-2), unit: mol m(-2)), the end-products of preceding fermentation by heterofermentative lactic acid bacteria (LAB) and subsequently accumulated in the sealed jars; (iii), after samples became unstable, the emission of CO2 represented a mixture of aerobic and anaerobic metabolites, whereas EtOH was anaerobic one, both compounds by yeasts; and (iv) time lags (maize: ca. 40 h, ryegrass: ca. 100 h) between CO2 and EtOH emissions were observed during the aerobic-unstable period. These findings contribute to our understandings of aerobic deterioration in silage and resulting pollution to air, providing supports for optimization of on-farm silo management to minimize the gas/VOC emissions from silage production.

Aerobic deterioration and resulting losses in silage are of worldwide concern to livestock managers. To mitigate degeneration of silage quality during feed-out, diverse chemical and biological additives have been developed. To allow efficient assessment of these additives, integrated chemical, microbiological and technological approaches are required but current methods are inadequate. Here we present an innovative mechatronic solution, combining robotic electronic gas detection (e-nose) of the fluxes of carbon dioxide (CO2) and ethanol (EtOH) with in situ measurements of oxygen (O2) concentration, pH and substrate temperature (Tsi). Nine sample chambers allow complex experimental design. The efficacy of the multi-sensor-based system, by documenting the oxidative degradation of maize silage (four control samples and four treated with a Lactobacillus bio-additive), demonstrated: (i) O2 is shown to be a potential indicator of microbial activity, initially stable at 18.20 vol% then declining to 6.1.12.5 vol%; (ii) Tsi and CO2 exhibited similar dynamics, in opposite sense, rising with the decline of O2; (iii) pH increased but lagged the decline of O2, and (iv) EtOH efflux increased only after O2 was substantially depleted to 5.8.13.4 vol%. The positive effect of the additive has been observed from all parameters measured in situ. This automated measurement system provides a new technique and experimental method to facilitate silage research and gas-emission investigations related to silage production.

Anaerobic lactobacillus (LAB) fermentation is key to production of silage. Tracking the dynamics of bacterial metabolism is important for the improvement of LAB fermentation and for evaluation of potential additives. This is currently limited by available ex situ analytical methods, while commercial sensors of lactic and acetic acid content remain unavailable. Here we validate an in situ pH sensor and devise a model-sensor package and a mini-fermenter system (1.5 L) for on-line analysis of LAB fermentation. By the fusion of the model based on mirror mapping principle and the time course of pH measured in situ, a general solution of the dynamic accumulation of organic acid (DAOA) and percentage yield of organic acid (PYOA, 0 similar to 100 %) is obtained as a function of time. We link PYOA to the initial and final values of lactic and acetic concentrations analyzed ex situ to obtain specific solutions for the time courses of lactic and acetic acid production. We demonstrate the model-sensor system with fermentation of both maize and ryegrass, capturing the dynamic patterns of fermentation, including the rapid depletion of O-2 in the initial aerobic phase (maize: approximate to 1.5 h, ryegrass: approximate to 9.2 h), the exponential decline of pH (R-2 >= 0.99, RMSE <= 0.043) in the subsequent anaerobic phase, and metabolic feedbacks of pH on instantaneous acid production (Delta pH; inflection at pH 5), and on cumulative yields of total acidity and specific organic acids. These are all previously unavailable data streams.

Hypothesized effects of aerosol deposition on plant water balance have been difficult to establish. This is due to variability between species, stomatal response to the treatment itself, and to environmental effects. Here we attempt a quantitative evaluation with a defined aerosol application, a paired leaf experimental design, and immobilized stomata.Attached leaves of poplar were treated with ammonium nitrate aerosol. After 17 or 20 days for deliquescence to develop an aqueous film, leaves were excised and stomata held closed with abscisic acid or open with fusicoccin. Transpiration and stomatal conductance were measured in a greenhouse with a porometer and leaf health was assessed by fluorescence.Median stomatal conductance was increased significantly, by 60 and 65%, following aerosol loading of 31.3 μg cm-2 in ABA- and FC-treated leaves, respectively.Aerosol induced transpiration, probably associated with a liquid film that lines the stomatal pore and not effectively regulated by stomatal closure, may be significant in magnitude. As aerosol deposition is ubiquitous, and its chemical nature may be changing, this factor should be considered in models of transpiration from leaf to canopy scale.### Competing Interest StatementThe authors have declared no competing interest.

Silage is produced worldwide for both livestock feeding and biogas production. Sustainable silage production requires characterization and mitigation of potential effects on environmental quality, particularly from greenhouse gas emissions during the production cycle. Ex-situ sampling has demonstrated that major emissions are carbon dioxide (CO2) and ethanol (EtOH). In-situ gas measurements from farm silo and bale silage are rare and may be important to improve our knowledge of the physical and biochemical causes, and constraints on these gas emissions. This study focused on tracking the kinetics of CO2 and EtOH emissions from bale maize silage, with real-time identification, quantification and separation of aerobic and anaerobic respiratory components in the period following opening of the silage. For this, an automatic multi-sensor gas-flux chamber (AMGC) was developed. Three bales (mean weight: 890 kg) of maize silage were tested (n = 3). Oxygen (O-2) and temperature (T-si) sensors were co-located at 10- and 20-cm behind the open face of the bales. Over the two weeks of the experiment we observed: (i) significant initial discharge of CO2 across the open face (1.68-2.55 mol m(-2) h(-1)) and EtOH (0.027-0.034 mol m(-2) h(-1)); (ii) peak CO2 emission occurred when O-2 concentration (10 cm depth) was 3 similar to 8% vol., while peak EtOH emission occurred below 2% vol. O-2, (iii) dynamic conversion of O-2 to CO2 from aerobic respiration; and (iv) the cumulative emission of EtOH during the anaerobic period was 4-6 times greater than that during aerobic plus semi-aerobic periods. These novel measurements provide mechanistic understanding, and may facilitate improved management of silage production to minimize environmental impact and aerobic loss of silage.

Hygroscopic aerosols deposited to leaves are a local water vapor sink and can affect the water balance of plants by deliquescence and the formation of hydraulic films that penetrate into the stomata. Stomatal responses to aerosols and vapor pressure deficit(VPD) were investigated in two poplar clones grown hydroponically in ventilated greenhouses with and almost without ambient aerosols.With increasing VPD, transpiration increased in ANI, the more anisohydric clone, and decreased in ISO, the more isohydric clone, while aerosols had little effect. In ANI, stomatal conductance (gsw) and photosynthesis (A) decreased slightly with increasing VPD, but significantly with exposure to aerosols. Leaf carbon isotopes confirmed the long-term reduction in stomatal aperture by aerosols. In ISO, gsw and A decreased strongly with increasing VPD. Aerosols had no effect on stomatal conductance in ISO, but increased the minimum leaf conductance and decreased the turgor loss point. In both clones, aerosols reduced stomatal density by >20%, indicating increased water scarcity.Aerosols enhance the transmission of atmospheric dryness to the leaf, with plant responses depending on their isohydricity. Sensitive stomatal closure of isohydric plants is an effective adaptation to atmospheric dryness, but aerosol accumulation mediates a liquid pathway for water loss that undermines stomatal control.### Competing Interest StatementThe authors have declared no competing interest.

The degree to which ozone (O-3) exposure and drought affect stomatal control of water loss and respond to environmental stimuli such as varying light is poorly characterized. To that end, we exposed Pima cotton to chronic O-3 exposure (month-long daytime exposures) with and without sufficient water, as well as short term acute O-3 exposure and varying light levels to understand stomatal kinetics. Chronic, month-long exposure to moderately high O-3 (similar to 114 ppb) reduced daytime steady state stomatal conductance (g(s)), as did water deficit. Both stomatal opening and closing displayed dose specific, "sluggish" responses to step-changes in illumination with acute, 1-day, O-3 exposures of 0, 50, 100, and 125 ppb. At higher concentration (150 ppb), stomatal control of both opening and closing was degraded. Altered steady state and dynamic stomatal function suggest that elevated ambient O-3, expected to increase in the future, may increasingly influence field water management and appropriate crop choices.

The biochemical reactions of aerobic microbial respiration (AMR) suggest that silage temperature (T-si) rise, oxygen (O-2) consumption and carbon dioxide (CO2) emission may be equally useful as indicators of silage deterioration during feed-out, but only temperature has been used extensively to assess aerobic stability. Here we extend the study of aerobic stability to incorporate AMR of silage by developing a novel experimental cell integrated with multiple sensors. Silage samples, ensiled from a triticale crop, were made in twelve air-tight barrels (60 L), packed to bulk densities of 190 or 250 kgm(-3) dry matter (DM). T-si and O-2 measurements were co-located at 15- and 30-cm behind the working face. CO2 was measured as flux across the working face. The experimental period of aerobic exposure was 7 days. We provide the first reports of: (i) distinct aerobic responses of these parameters, showing that T-si varied with CO2 in phase but with O-2 out-of phase; (ii) CO2 flux was dominated initially by anaerobic discharge and subsequently by aerobic products; (iii) linear relationships between aerobic reheating and both O-2 consumption (0.994 >= R-2 >= 0.815, P < 0.01) and CO2 flux (0.981 >= R-2 >= 0.464, P < 0.01); and (iv) variable magnitude of daily aerobic production of CO2 per kg DM from 2.3 to 133.4 mmol kg d(-1). These results demonstrate that the novel multi-sensor technique has powerful capacity to provide insight into AMR of silage and thus provide more detailed information to guide silage management than previous measurements of aerobic stability. (C) 2021 IAgrE. Published by Elsevier Ltd. All rights reserved.

The microbiome in silage may vary substantially from the onset to the completion of fermentation. Improved additives and inoculants are being developed to accelerate the ensiling process, to enhance fermentation quality, and to delay spoilage during feed-out. However, current methods for preselecting and characterizing these amendments are time-consuming and costly. Here, we have developed a multi-sensor mini-bioreactor (MSMB) to track microbial fermentation in situ and additionally presented a mathematical model for the optimal assessment among candidate inoculants based on the Bolza equation, a fundamental formula in optimal control theory. Three sensors [pH, CO 2 , and ethanol (EtOH)] provided data for assessment, with four additional sensors (O 2 , gas pressure, temperature, and atmospheric pressure) to monitor/control the fermentation environment. This advanced MSMB is demonstrated with an experimental method for evaluating three typical species of lactic acid bacteria (LAB), Lentilactobacillus buchneri (LB) alone, and LB mixed with Lactiplantibacillus plantarum (LBLP) or with Enterococcus faecium (LBEF), all cultured in De Man, Rogosa, and Sharpe (MRS) broth. The fermentation process was monitored in situ over 48 h with these candidate microbial strains using the MSMB. The experimental results combine acidification characteristics with production of CO 2 and EtOH, optimal assessment of the microbes, analysis of the metabolic sensitivity to pH, and partitioning of the contribution of each species to fermentation. These new data demonstrate that the MSMB associated with the novel rapid data-processing method may expedite development of microbial amendments for silage additives.

Stem water content (StWC) of plants is an important parameter for assessing plant response to drought stress in arid and semi-arid areas and for irrigation scheduling. The measurement accuracies of in-situ non-invasive approaches are degraded by plant growth and by diurnal changes in stem diameter associated with water content. Here we develop a frequency-domain (FD) dielectric sensor operating at 100 MHz with an innovative interdigitated-electrodes (IE) probe design for measuring StWC. We characterize the performance of the IE sensor and compare it with a previously described pair-strap-ring-electrodes (2RE) FD sensor. Simulations and experimental measurements were conducted to assess the electric field distribution and volume of sensitivity (VOS) of each probe, the sensitivity of each probe to stem diameter and the accuracy of each sensor for determining StWC of three apple trees in a greenhouse environment. The simulation analysis and the measurement showed that the IE probe has a smaller but denser VOS than the 2RE probe. The sensitivity test showed that the new IE probe (0.85 mV mm(-1), R-2 = 0.7108) was less susceptible to stem diameter variation in comparison with the 2RE probe (32.83 mV mm(-1), R-2 = 0.9977). The observations in the greenhouse showed that the three apple trees (AT-1, AT-2 and AT-3) experienced a daily dehydration-rehydration cycle and the averaged midnight-to-predawn StWC gradually decreased without irrigation. According to the reference values of the maximum daily trunk shrinkage (MDS) reported by a previous study, both AT-2 and AT-3 may experience water deficit before the irrigation. Besides, the stem diameter variation decreased the measurement accuracy of 2RE sensor to be similar to 0.0410 cm(3) cm(-3) mm(-1). The stronger electric field intensity of the IE probe and its less susceptible to stem diameter variation make the new IE dielectric sensor an improved method for accurate in-situ measurement of diurnal stem water content.

High quality silage containing abundant lactic acid is a critical component of ruminant diets in many parts of the world. Silage deterioration, a result of aerobic metabolism (including utilization of lactic acid) during storage and feed-out, reduces the nutritional quality of the silage, and its acceptance by animals. In this study, we introduce a novel non-disruptive dual-sensor method that provides near real-time information on silage aerobic stability, and demonstrates for the first time that in situ silage temperature (Tsi) and pH are both associated with preservation of lactic acid. Aerobic deterioration was evaluated using two sources of maize silage, one treated with a biological additive, at incubation temperatures of 23 and 33 °C. Results showed a time delay between the rise of Tsi and that of pH following aerobic exposure at both incubation temperatures. A 11 to 25% loss of lactic acid occurred when Tsi reached 2 °C above ambient. In contrast, by the time the silage pH had exceeded its initial value by 0.5 units, over 60% of the lactic acid had been metabolized. Although pH is often used as a primary indicator of aerobic deterioration of maize silage, it is clear that Tsi was a more sensitive early indicator. However, the extent of the pH increase was an effective indicator of advanced spoilage and loss of lactic acid due to aerobic metabolism for maize silage.

Soil water potential is a key variable that determines water flow and indicates water availability and content. Although diverse techniques and methods have been developed for water potential measurement in unfrozen soils, most commercial techniques such as dielectric soil water potential (DSWP) sensors are not applicable for frozen soils due to potential errors of the dielectric measurement caused by ice formation within the sensor probes. Rather than directly recording sensor readings, these commercial DSWP sensors have to indirectly estimate soil water potential under equilibrium conditions by temperature measurement and the Clapeyron equation. Here we develop a mathematical model to correct the ice induced measurement error of the DSWP sensor in frozen soils. The DSWP sensor tested in this research was self-developed with a perforated cylinder coaxial (PCC) probe filled with a porous medium (gypsum). The central electrode was a temperature sensor (Pt100) replacing the usual steel pin. Sensor performance was demonstrated in a non-saline, loamy soil, by installing one sensor (DSWP-1) in a wetted soil sample prior to soil freezing, with two additional sensors (DSWP2 and DSWP-3) installed later in frozen soil, prior to stepwise thawing. The results show that ice formed in the porous gypsum of the DSWP-1 sensor during soil freezing, as would be expected in the field with liquid water initially present to enter the probe. In comparison, no ice formed in the porous gypsums of the DSWP-2 and DSWP-3 sensors during the stepwise thawing process, allowing directly measurement of soil water potential in frozen soils and acting as a reference to develop an ice correction model based on a dielectric mixing model for the ice-formed DSWP-1 sensor to improve accuracy of soil water potential measurement. With the ice correction model, the RMSE between the readings of the DSWP-1 sensor and the reference values determined by the DSWP3 sensor was decreased from 1.065 MPa to 0.491 MPa. In general, the ice correction model developed here can be used to improve accuracy of soil water potential measurement during soil freeze-thaw process using the DSWP sensor or other dielectric sensors and may extend application of the DSWP sensor to frozen soils under nonequilibrium conditions in the field.

Stomatal pore area is heterogeneous across leaf surfaces. This has been considered as “patchy stomatal conductance,” and may have substantial implications for photosynthetic efficiency. Aerosols have always been important elements of plant environments, but their effects on stomatal control of plant water relations, and stomatal heterogeneity specifically, have not been considered. Here we evaluate the spatial coordination of pore area in the glabrous and homobaric leaves of Vicia faba grown under two aerosol treatments and measured at four levels of VPD. We construct a large dataset (n > 88,000 discrete comparisons) of paired pore areas and distances between the pores. Plants were grown in ambient urban air and in filtered air (FA) to determine the effect of ambient aerosol on stomatal properties. Pore area exhibited spatial organization, as well as considerable variability among closely co-located pores. The difference between pore areas was positively correlated with the distance between the pores, in both aerosol treatments and at all VPDs. However, aerosol deposition reduced both the magnitude of variability between pores and the rate at which this variability increased with pore separation distance. These data support previous conclusions that deposition of hygroscopic aerosol may create a thin aqueous film across the leaf surface that connects neighboring stomata to each other and to the leaf interior. Aerosol impacts on stomatal heterogeneity and gas exchange are not adequately considered in current assessments of stomatal control.

Evapotranspiration (ET) plays an important role in water and energy balance at the surface-atmosphere interface. It is widely reported that near-surface soil water content (SWC) or soil water potential (SWP) significantly affects ET and this parameter has been incorporated into the FAO Penman-Monteith (FAO-PM) model for prediction of ET during crop growth seasons. However, there is little information on the effect of SWC or SWP on prediction of ET during soil freeze-thaw cycles in winter. We present an experiment conducted at a demonstration farm with a crop of winter wheat, over two winters near Beijing, China. A lysimeter system equipped with a weather station was used to measure the ET flux and meteorological data. Unfrozen soil water content (USWC) and soil temperature (T-soil) were measured using dielectric tube sensors (DTS) and digital temperature sensors, respectively. SWP was determined by measured USWC and a soil moisture characteristic (SMC) curve derived from the soil freezing characteristic (SFC) curve and the Clapeyron equation in frozen soil. Detailed measurements in year 1 showed that the FAO-PM model exhibited a complex error pattern, underestimating ET from unfrozen soil but overestimating ET from stable frozen soil. To address these errors, we define a freezing stress index (K-sf) as a function of SWP. Incorporation of K-sf as a modifier of the standard crop coefficient in the FAO-PM model improved prediction of ET (RMSE declined from 0.424 to 0.187 mm day(-1), in year 1). These data revealed a correlation between SWP near the soil surface (<10 cm) and measured ET over freezing and thawing cycles. We incorporated a coupled heat and water transfer (CHWT) model into the improved FAO-PM model to predict USWC, SWP and ET throughout the winter of year 2 from current meteorological data as upper boundary conditions, initial measurements of ET, USWC and Tsoil as initial conditions, and Ksf and soil hydraulic properties optimized in year 1. The results showed that ET estimation was significantly improved, with RMSE reduced from 0.323 to 0.281 mm day(-1) using the combined (FAOPM-K-sf-CHWT) model. Model error primarily derived from an underestimation of simulated SWP during soil freezing process. The combined model extends the utility of the FAO-PM model to non-cropping seasons including winter in temperate climates and reduces the data requirements for accurate prediction of ET from intermittently frozen soil.

Documentation in the field of the longitudinal progression of freezing in woody stems during winter has recently become feasible due to development of advanced instrumentation. Similar techniques to detect the radial progression of freezing fronts in the stem have remained challenging and, so far, unresolved. Here we address this problem with a smart sensor, based on an inner fringing dielectric technique, but combined with a new analytical model of radial freezing-thawing-fronts. These fronts, occurring in night and daytime of winter, respectively, are considered as vectors, both moving radially from the outside of the stem inward. We present laboratory calibration data and a field experiment in a 14-year old apple orchard to demonstrate the novel capability of this noninvasive sensor for in situ determination of ice content. We track the diurnal and seasonal variation of ice content, identify the radial location of the freezing/thawing-front, link this to anatomical features of the stem, and characterize hysteresis in freezing and subsequent thawing. We document homeostasis of total tissue water content during winter which allowed quantification of ice and liquid water content over both diurnal and seasonal cycles. Moreover, the progressive, day-to-day, decrease in liquid water during cold acclimation in autumn and increase during de-acclimation in spring are shown, along with the associated transpirational fluxes. These data contribute to fundamental knowledge of the water relations of trees, demonstrate a practical technique to monitor multiple trees in the field, and thus provide insight into the ecophysiological processes involved as trees overwinter.

Origins of abscisic acid (ABA)-mediated metabolic control of stomatal conductance have been suggested to be recent, based on a gradualistic model of stomatal evolution. In ferns, steady-state stomatal conductance (gs ) was unresponsive to ABA in some studies, supporting this model. Stomatal kinetic responses to ABA have not been considered. We used dynamic gas exchange methods to characterise half times of stomatal opening and closing in response to step changes in light, across a range of ABA exposures in three diverse taxa. All taxa had asymmetric kinetics, with closure slower than opening in fern and cedar, but faster than opening in soybean. Closing was fastest in soybean but opening was slowest. Stomatal kinetics, particularly for closure, responded to ABA in all three taxa. Steady-state gs did not respond significantly to ABA in fern or cedar but responded strongly in soybean. Stomatal kinetics were responsive to ABA in fern. This finding supports a contrasting, single origin model, with ABA-mediated regulation of stomata arising early, in conjunction with stomata themselves. Stomatal kinetics are underutilised. Differential responses of opening and closing rates to environmental and hormonal stimuli may provide insights into phylogeny and stomatal regulatory strategies with potential application to selection for crop improvement.

Carbon dioxide (CO2) is a principal byproduct of various chemical, biological and biochemical processes. CO2 has been measured using various advanced sensors, but a limiting technical challenge has been resolving independent streams of CO2 produced by processes occurring simultaneously. The magnitude and kinetics of each stream may be chemically, biologically or/and physically informative, but such partitioning has received lithe attention and successful case studies remain rare. In silage production, CO2 flux, an important indicator of aerobic deterioration, microbial activity or oxidative rate of silage, derives from two different pools: gas accumulated in the pores during the early anaerobic phase, and current real-time production of CO2 as oxygenated air enters the silage across the exposed face after opening for feed-out. The former is regarded as a noise confounding the signal and the latter reflects current degradation of the silage. Using a self-developed automatic sensor system with novel signal decomposition, we successfully partitioned CO2 flux into two independent streams derived from the two distinct pools in maize silage, following two independent processes: a physical venting of stored gas through a tortuous diffusive pathway, and a biochemical process generating gas in real time. Three silage samples, treated with a chemical or a biological additive, or left untreated, were tested. The signal decomposition found two best-fit functions (0.8034 <= R-2 <= 0.9036), a quadratic CO2 discharge function and an exponential CO2 production function, for characterizing these distinct processes. These results demonstrate chemical sensor with powerful data-processing capability to resolve the complexity of dual-pool CO2 emission.

Near-surface soil water content (NSWC) is an important parameter for characterizing hydrological processes, water and vapor exchange at the soil-atmosphere boundary, and potential biological productivity. Here we develop a dielectric based frequency-domain (FD) impedance sensor operating at 100 MHz, with a novel coaxial probe design and a temperature sensor embedded in the circuit board. This perforated cylinder coaxial (PCC) sensor provides simultaneous measurements of volumetric soil water content (VSWC) and of temperature. The temperature measurement allows signal correction for the temperature response of the circuit board and of the permittivity of soil water. We characterize the performance of the PCC sensor and compare it with alternative 3-pin- and 2-pin-electrode FD impedance sensors each using a similarly performing circuit board. A series of theoretical analyses and experiments were conducted, including (i) sensors calibration, (ii) temperature effects and their correction, (iii) soil volume sensed by each sensor through simulation analysis and a stepwise soil removal (SSR) test and (iv) accuracy comparison of the three sensors when applied for the NSWC measurements. The calibration results verified that the PCC, 3-pin and 2-pin probes were suitable to measure VSWC (RMSE <= 0.0142 cm(3) cm(-3)). The simulation analysis using High Frequency Structure Simulator software (HFSS) indicated that the novel PCC probe had a symmetrical distribution of the E-field, wholly contained within the cylinder, avoiding leakage of the E-Field into air at the soil-atmosphere interface and removing the dependency of sensed volume on VSWC. The results of the SSR test showed that the E-field distributed outside the receiving electrode of the PCC probe could be ignored whereas that of both pin-type electrodes was distributed outside of the receiving electrode to a distance that depended on VSWC (i.e. up to 8 mm for 3-pin and up to 11 mm for 2-pin designs when VSWC > 0.17 cm(3) cm(-3)), which corresponds to the simulation analysis. Moreover, the new PCC probe provided more accurate NSWC measurement than 3-pin or 2-pin probes because the E-field was contained within the perforated cylinder, avoiding E-field leakage and fixing sensed soil volume independent of VSWC. The pin-structure probes appear to perform best when installed horizontally in the soil at least 11 mm below the surface.