Root Electrical Capacitance Research Articles

Effect of weather, nitrogen fertilizer, and biostimulators on the root size and yield components of Hordeum vulgare

Abstract In this study, the effect of nitrogen doses (52, 80, 110, 140 kg/ha N) and the application of biostimulant preparations containing Ascophyllum nodosum L. algae extract were assessed. During the years 2018–2019, the influence of the preparations on the electrical capacity of the roots (C R) and yield components of spring barley was determined. Root electrical capacitance was determined in growth stages 45–50, 55–65, and 70–75 according to the BBCH-scale. The best phases of vegetation growth for the application of biostimulators with Ascophyllum nodosum extract were the barley tillering and elongation phases. This application increased C R while reducing the amount of N required to achieve similar or higher production of barley yield components compared to high N treatments. The root electrical capacitance, the number of productive tillers, and the number of grains per plant were significantly influenced (p > 0.05) by the weather of the year. The number of productive tillers was closely correlated with C R (r = 0.912**) as well as the number of grains per plant (r = 0.859**) and their weight (r = 0.850**). These relationships were the highest at the beginning of the grain formation (BBCH 70–75). Foliar biostimulation was not very effective in the dry year of 2018. The problem may be the foliar application itself. The effect of foliar application is strongly dependent on weather conditions and may be ineffective in many cases. We recommend the foliar application of effective biostimulants in tillering and elongation phases. They can reduce production costs and environmental pollution by reducing the amount of fertilizer needed while maintaining yields.

Root Electrical Capacitance Can Be a Promising Plant Phenotyping Parameter in Wheat.

As root electrical capacitance (CR*) was assumed to depend on the stem properties, the efficiency of measuring CR* at flowering for whole-plant phenotyping was assessed in five wheat cultivars in three replicate plots over two years. Linear regression analysis was used to correlate CR* with plant-size parameters and flag-leaf traits (extension and SPAD chlorophyll content) at flowering, and with yield components at maturity. The plot-mean CR* was correlated with the plot leaf area index (LAI), the chlorophyll quantity (LAI×SPAD), and the grain yield across years. At plant scale, CR* was found to show the strongest positive regression with total chlorophyll in the flag leaf (flag leaf area × SPAD; R2: 0.65-0.74) and with grain mass (R2: 0.55-0.70) for each cultivar and year (p < 0.001). Likewise, at plot scale, the regression was strongest between CR* and the LAI×SPAD value (R2: 0.86-0.99; p < 0.01) for the cultivars. Consequently, CR* indicated the total plant nutrient and photosynthate supply at flowering, which depended on root uptake capacity, and strongly influenced the final yield. Our results suggested that the polarization of the active root membrane surfaces was the main contributor to CR*, and that the measurement could be suitable for evaluating root size and functional intensity. In conclusion, the capacitance method can be applied for nondestructive whole-plant phenotyping, with potential to estimate root and shoot traits linked to the nutrient supply, and to predict grain yield. CR* can be incorporated into allometric models of cereal development, contributing to optimal crop management and genetic improvement.

Understanding the trade–off between lodging resistance and seed yield, and developing some non–destructive methods for predicting crop lodging risk in canola production

Efficient nitrogen (N) nutrient management is important for developing sustainable strategies to increase seed yield while reducing negative environmental impacts. Motivation to increase seed yield by appropriately increasing N application rates would make crop lodging a potential problem. Fewer studies have been conducted to elucidate the trade–off between yield gain and lodging susceptibility in canola ( Brassica napus L. ), and a non–destructive and high–throughput assessment of lodging is seriously lacking. In this regard, a field study consisting of two varieties and five combinations of rates and timing of N application was conducted to explore the strength of their trade–offs for better N fertilization recommendation and to determine the feasibility of non–destructive technique for diagnosing canola lodging susceptibility. Two non–destructive techniques including root electrical capacitance and normalized difference vegetative index (NDVI) were verified in this study. The susceptibility of stem and root lodging were quantified by “safety factor” method. The results showed that there was a trade–off between seed yield and lodging resistance under conditions of seed yield greater than 1.3 t ha –1 . Under high–yielding condition of 2021 cropping season, split–N treatment, 50 kg N ha –1 at preplant plus 50 kg N ha –1 topdressed at the 6–leaf stage, increased seed yield by 20% and lodging resistance by 38% for hybrid ‘Invigor L233P’, compared with the equivalent preplant–only N application. However, under low–yielding condition, split–N treatments did not always show advantages over the equivalent preplant–only N treatments in terms of lodging resistance and seed yield, whereas the highest seed yield was generally attained under the split–N application in all experimental years. Root capacitance and impedance were significantly correlated with root morphological traits, which in turn affected lodging resistance and seed yield, while NDVI was closely related to lodging resistance (P < 0.01). A split–N application strategy with moderate N rates (100–150 kg N ha –1 ) can be highly recommended for canola production in eastern Canada. Indirect prediction of lodging susceptibility through root electrical measurements and NDVI mapping have high applicability due to their low cost and non–destructive properties, and are expected to serve as high–throughput techniques for guiding N fertilizer management to improve seed yield, while reducing lodging risk. • The trade–off between canola yield and lodging susceptibility was elucidated. • Split–N application with moderate rates can be recommended for canola production. • NDVI and root capacitance were feasible for diagnosing lodging susceptibility risk.

Optimising nitrogen management strategies to minimise lodging risk while sustaining high seed yield in rapeseed

Appropriate nitrogen (N) fertiliser management is an essential strategy for improving the productivity of rapeseed (Brassica napus L.) plants. However, the increased lodging risks under higher yield potentials with enhanced N application rates have largely been overlooked. Few studies have elucidated the trade-off between lodging resistance and seed yield, and a non-destructive method for in situ evaluation of crop lodging is urgently needed. A field study with five site-year environments was conducted to elucidate the trade-off between seed yield and lodging susceptibility under various N application rates in two varieties, and to evaluate the feasibility of using root electrical capacitance (EC) and impedance (EI) as non-destructive techniques for diagnosing the risk of crop lodging. Seed yield and lodging susceptibility (quantified by safety factor, lodging angle, and visual lodging score methods) increased with increasing N application rates. The natural crop lodging occurred in 2 out of 5 site-year environments, which agreed well with lodging resistance quantified by safety factor. A strong relationship between lodging susceptibility and seed yield was found (R2 = 0.31**– 0.82***, except 1 out of 5 site-year environments), and evidenced by a principal component analysis (PCA) and a structural equation model (SEM). EC was positively correlated to several root morphological parameters of taproot (R2 = 0.18*– 0.93***), lateral root (R2 = 0.17*– 0.61***), and total root system (R2 = 0.26**– 0.93***); whereas EI was negatively correlated to these root morphological parameters. In addition, EC and EI were found to be closely related to seed yield and root lodging susceptibility, through the Pearson correlation and partial correlation analysis. In conclusion, a moderate N application of 240 kg N ha−1 can fully explore the yield potential and could be recommended for rapeseed production. Root electrical measurements (EC and EI) can be regarded as high-throughput techniques for predicting lodging susceptibility.

Root electrical capacitance as an indicator of wheat growth and yield in a free-air carbon dioxide enrichment (FACE) experiment

Background and aimsThis study was the first to test the efficiency of monitoring root electrical capacitance (CR*) non-destructively in the field to evaluate crop development under different environmental conditions.MethodsA free-air CO2 enrichment (FACE) experiment was performed with two winter wheat cultivars, two levels (low and high) of nitrogen supply and two (ambient and elevated) of [CO2] in three replicate plots over two years. The validity of CR* as a proxy for root uptake activity was confirmed by tracking the ceptometer-based leaf area index (LAI).ResultsRepeated CR* measurements clearly demonstrated the seasonal dynamics in root development, with a peak at flowering, and the delayed growth in the second year caused by the unfavourable meteorological conditions. From the vegetative to flowering stages, CR* was strongly correlated with LAI (R2: 0.897–0.962). The positive effect of higher N supply and elevated [CO2] on crop growth was clearly indicated by the higher CR* values, associated with increased LAI, shoot dry mass (SDM) at flowering and grain yield (GY). The maximum CR* was closely related to GY (R2: 0.805 and 0.867) when the data were pooled across the N and CO2 treatments and the years. Unlike CR* and GY, SDM and LAI were significantly lower in the second year, presumably due to the enhanced root/shoot ratio induced by a severe spring drought.ConclusionsThe present results convincingly demonstrated the potential of the in situ root capacitance method to assess root responses dynamically, and to predict crop GY.

Electrical Capacitance versus Minirhizotron Technique: A Study of Root Dynamics in Wheat-Pea Intercrops.

This study evaluated the concurrent application and the results of the root electrical capacitance (CR) and minirhizotron (MR) methods in the same plant populations. The container experiment involved three winter wheat cultivars, grown as sole crops or intercropped with winter pea under well-watered or drought-stressed conditions. The wheat root activity (characterized by CR) and the MR-based root length (RL) and root surface area (RSA) were monitored during the vegetation period, the flag leaf chlorophyll content was measured at flowering, and the wheat shoot dry mass (SDM) and grain yield (GY) were determined at maturity. CR, RL and RSA exhibited similar seasonal patterns with peaks around the flowering. The presence of pea reduced the maximum CR, RL and RSA. Drought significantly decreased CR, but increased the MR-based root size. Both intercropping and drought reduced wheat chlorophyll content, SDM and GY. The relative decrease caused by pea or drought in the maximum CR was proportional to the rate of change in SDM or GY. Significant linear correlations (R2: 0.77–0.97) were found between CR and RSA, with significantly smaller specific root capacitance (per unit RSA) for the drought-stress treatments. CR measurements tend to predict root function and the accompanying effect on above-ground production and grain yield. The parallel application of the two in situ methods improves the evaluation of root dynamics and plant responses.

Prediction of wheat grain yield by measuring root electrical capacitance at anthesis

1. Bedoussac L. and Justes E., 2011. A comparison of commonly used indices for evaluating species interactions and intercrop efficiency: Application to durum wheat-winter pea intercrops. Field Crops Res., 124, 25-36. https://doi.org/10.1016/j.fcr..... CrossRef Google Scholar

Crop lodging, pod fertility and yield formation in canola under varying degrees of short‐term heat stress during flowering

AbstractThere has been little research on crop lodging and yield determination in response to varying degrees of heat stress in canola. This research aimed to examine root morphology, pod fertility, seed yield and crop lodging of two canola genotypes subjected to normal temperature (23/17°C, light/dark, as CK), and three elevated temperature regimes imposed at flowering for a short term (10 days), namely CK+2 (25.0/22.0°C, light/dark), CK+4 (27.0/24.0°C) and CK+6 (29.0/26.0°C), in a controlled growth facility. Elevated temperature treatment, CK+4 and CK+6, displayed a significant adverse effect on seed yield and stem lodging. Compared to the CK, a significant yield loss of 35.6% and 48.7% in CK+4 and CK+6, respectively, was mainly due to poor pod fertility. This was evident from the smaller number of total filled pods (−21% in the CK+4 and −25% in the CK+6), low success ratio of pod developed (−25%, CK+4 and −29%, CK+6) and poor pollen viability (−36%, CK+4 and −50%, CK+6), averaged across both genotypes. Lateral root development was sensitive to the elevated temperature treatment, showing significant reductions in the lateral root morphology (8.0%–28.5%), while the taproot was relatively tolerant to the elevated temperature stress. A strong relationship between root electrical capacitance and lateral root morphology (R2 &gt; .74**) indicates that electrical measurements could be used as a non‐destructive method for evaluating root parameters under elevated temperatures. Higher risk of stem lodging (21.4% lower stem safety factor) compared to the CK was evident under severe elevated temperature stress, as ascribed from the reduced stem bending strength that was caused by the deteriorating stem mechanical properties such as decreased flexural rigidity and weakened vascular bundle size (i.e. stunted fibre cell, and thinned size of fibre wall, deteriorated secondary xylem and smaller secondary phloem). These results were further verified by the principal component analysis and structural equation model. The root lodging risk was not influenced by the elevated temperature regime, primarily due to the unaffected anchorage strength and height of the centre of gravity. This information will be useful in improving lodging resistance and alleviating the related impact of heat stress in canola.

Effect of Plasma Activated Water Foliar Application on Selected Growth Parameters of Maize (Zea mays L.)

Utilization of plasma activated water (PAW) for plant growing is mainly connected with the treatment of seeds and subsequent stimulation of their germination. A potential of PAW is its relatively simple and low-cost preparation that calls for studying its wider application in plant production. For this purpose, a pot experiment was realized in order to prove effects of the foliar PAW application on maize growth. The stepped PAW foliar application, carried out in 7-day intervals, led to provable decrease of chlorophyll contents in leaves compared to the distilled water application. The PAW application significantly increased root electrical capacitance, but it had no provable effect on weight of the aboveground biomass. Chlorophyll fluorescence parameters expressing the CO2 assimilation rate and variable fluorescence of dark-adapted leaves were provably decreased by PAW, but quantum yield of photosystem II electron transport was not influenced. A provably higher amount of nitrogen was detected in dry matter of plants treated by PAW, but contents of other macro- and micro-nutrients in the aboveground biomass of maize were not affected. Results of this pilot verification of the PAW application have shown a potential for plant growth optimization and possibility for its further utilization, especially in combination with liquid fertilizers.

Winter oilseed rape semi‐dwarf hybrids are not discriminated by front‐border effects in yield trials

AbstractFor oilseed rape (Brassica napus L.), hybrid varieties of two growth types, semi‐dwarf and normal, are on the market. So far, the acceptance of semi‐dwarf hybrids is very limited, though they have several advantages such as higher N efficiency and drought tolerance. It is undecided whether both growth types are influenced in the same way by front‐border effects in plot yield trials. This study analyzed if semi‐dwarf hybrids were discriminated against in yield trials, due to differences in the exploitation of the front‐border area, since they could not lean and grow as far into the adjacent path due to a reduced height compared to normal type hybrids. From 2016–2018, eight pairs of near‐isogenic hybrids, bzh semi‐dwarf and normal type hybrids, were grown in three environments, with three replications and two treatments: Plants were harvested with and without the plot front‐border, and seed and straw yields were determined. Root electrical capacitance was also measured. Semi‐dwarf hybrids outperformed normal type hybrids in seed yield in the dry season of 2018, whereas the reverse happened in the more humid season of 2017. Across environments, semi‐dwarf hybrids had a higher positive front‐border effect (11.2%) than normal type hybrids (9.6%), leading to a relative overestimation of semi‐dwarf hybrid yields. There was no significant difference in root electrical capacitance between growth types across environments. It could be concluded that semi‐dwarf hybrids were not disadvantaged with regard to front‐border effects in plot trials, when compared to normal type hybrids. However, elimination of the plot front‐border area might improve comparisons between semi‐dwarf and normal type cultivars.

Root capacitance measurements allow non-intrusive in-situ monitoring of the seasonal dynamics and drought response of root activity in two grassland species

Background and aimsIn this study, the potential of non-intrusive root electrical capacitance (CR) measurements for monitoring the seasonal changes and drought response of root activity was tested on two grassland species in a climate change experiment.MethodsCR was detected between a ground electrode inserted into the soil and a plant electrode attached to the stem of the perennial grass Stipa borysthenica and the biennial herb Crepis rhoeadifolia in control and drought plots throughout two growing seasons. A pilot study revealed that CR was strongly correlated with root biomass for a given time and soil water content. The effect of changing soil water content on the measured CR value was accounted for by means of species-specific experimental calibrations.ResultsRoot activity (CR) was found to peak at the flowering stage in late spring (S. borysthenica) or early summer (C. rhoeadifolia). Both the natural shortage of rainfall and the experimental summer drought reduced root activity in both species. Stipa borysthenica displayed great plasticity in root activity, including quick post-treatment recovery during the rainy autumn. The changes observed in root activity were similar to those previously recorded using conventional root investigation techniques (i.e. destructive, minirhizotron, ingrowth core) in temperate grasslands.ConclusionsRoot capacitance measurements proved to be adequate for monitoring root activity in situ in natural grassland. The method could be particularly useful in studies where plant injury or soil disturbance need to be avoided.

Selection of plant physiological parameters to detect stress effects in pot experiments using principal component analysis

Appropriate selection and well-timed measurement of plant developmental, morphological and physiological parameters are essential to maximize efficacy and minimize time consumption of experiments. To select for the most sensitive indicators of drought or salt stress, three independent pot experiments with diverse setups were analysed with 20–20 measured parameters. Parameters of plant growth, phenology and symbiotic interactions, visual stress symptoms, photosynthetic activity, nutrient composition and vitality were studied and the result matrices were evaluated with principal component analysis (PCA). Stress effects manifested in PC1 of two experiments and in PC2 of the third one. Traits assumed to be adequate for stress indication were characterized by high PC1 or PC2 loading values. Beside parameters of biomass production, growth and visible stress symptoms, less evident traits e.g. root electrical capacitance, membrane stability index in roots and leaves, relative water content of leaves and SPAD units were identified.

Root system size response of bzh semi-dwarf oilseed rape hybrids to different nitrogen levels in the field.

Background and AimsIn oilseed rape (Brassica napus) semi-dwarf hybrid varieties from crosses between bzh dwarf and normal-type lines are of increasing interest. They have improved nitrogen (N) uptake, N-utilization and N-use efficiency compared to normal types. This study aimed to elucidate whether these N-related effects can be explained by the bzh shoot growth-type alone or also by differences in root traits.MethodsRoot system size was measured using root electrical capacitance (EC) in field trials with two N levels in two sets of genotypes segregating for the bzh-locus: (1) 108 doubled haploid (DH) test hybrids in two seasons, 2010–2012, and (2) 16 near-isogenic hybrids in the 2016–17 season. Quantitative trait loci (QTL) for root EC were estimated in DH test hybrids. Seedling root architecture parameters were monitored in vitro.Key Results In vitro root growth showed a higher root: shoot ratio in bzh semi-dwarf hybrids. Root EC in field trials was higher at high N supply than at zero N fertilization. In most trials semi-dwarf hybrids had higher EC than normal-type hybrids, but they reduced root EC in response to N limitation more than normal types. Root EC was more heritable at the end of flowering (h2 = 0.73) than at the beginning of flowering (h2 = 0.36) in near-isogenic hybrids and had a lower heritability in trials of DH test hybrids (h2 = 0.27). A QTL for root EC in the genomic region of the bzh-locus on linkage group A06 was significant at zero N fertilization.ConclusionsRoot EC proved to be a meaningful method in oilseed rape breeding programmes targeting root system size. The greater reduction of semi-dwarf root EC compared to the normal type under low N supply with simultaneous increase in N efficiency implies that in roots it is not a question of ‘the more the merrier’ and that the bzh root system reacts highly economically when N is scarce.

Symbiotic Effectivity of Dual and Tripartite Associations on Soybean (Glycine max L. Merr.) Cultivars Inoculated With Bradyrhizobium japonicum and AM Fungi.

Soybean (Glycine max L. Merr.) is regarded worldwide as indisputably one of the most important crops for human food and animal feed. The presence of symbiotic bacteria and fungi is essential for soybean breeding, especially in low-input agricultural systems. Research on the cooperation between different microbial symbionts is a key to understanding how the health and productivity of the plant is supported. The symbiotic effectivity of dual and tripartite symbiotic agents was investigated in two pot experiments on different soybean cultivars with special regard to compatibility. In the Selection experiment, two out of sixteen soybean cultivars (Aliz, Emese) were chosen on the basis of their drought tolerance and used in all the other investigations. In the Compatibility experiment, the compatible coupling of symbiotic partners was selected based on the efficiency of single and co-inoculation with two Bradyrhizobium japonicum strains and two commercial arbuscular mycorrhizal fungal (AMF) products. Significant differences were found in the infectivity and effectivity of the microsymbionts. The rhizobial and AMF inoculation generally improved plant production, photosynthetic efficiency and root activity, but this effect depended on the type of symbiotic assotiation. Despite the low infectivity of AMF, inocula containing fungi were more beneficial than those containing only rhizobia. In the Drought Stress (DS) experiment, co-inoculated and control plants were grown in chernozem soil originating from organic farms. Emese was more resistant to drought stress than Aliz and produced a bigger root system. Under DS, the growth parameters of both microbially inoculated cultivars were better than that of control, proving that even drought tolerant genotypes can strengthen their endurance due to inoculation with AMF and nitrogen fixing bacteria. Root electrical capacitance (CR) showed a highly significant linear correlation with root and shoot dry mass and leaf area. The same root biomass was associated with higher CR in inoculated hosts. As CR method detects the absorptive surface increasing due to inoculation, it may be used to check the efficiency of the microbial treatment.

Application of Electrical Capacitance Method for Prediction of Plant Root Mass and Activity in Field-Grown Crops.

The root electrical capacitance (CR) method is suitable for assessing root growth and activity, but soil water content (SWC) strongly influences the measurement results. This study aimed to adapt the method for field monitoring by evaluating the effect of SWC on root capacitance to ensure the comparability of CR detected at different SWC. First a pot experiment was conducted with maize and soybean to establish CR–SWC functions for the field soil. Ontogenetic changes in root activity were monitored under field conditions by simultaneously measuring CR and SWC around the roots. The CR values were normalized using SWC data and experimental CR–SWC functions to obtain CR*, the comparable indicator of root activity. The effect of arbuscular mycorrhizal fungi (AMF) inoculation on the CR* and biomass of field-grown soybean was investigated. The pot trial showed an exponential increase in CR with SWC. CR–SWC functions proved to be species-specific. CR showed strong correlation with root dry mass (R2 = 0.83–0.87). The root activity (CR*) of field-grown crops increased until flowering, then decreased during maturity. This was consistent with data obtained with other methods. AMF inoculation of soybean resulted in significantly higher CR* during the late vegetative and early flowering stages, when destructive sampling concurrently showed higher shoot biomass. The results demonstrated that the root capacitance method could be useful for time course studies on root activity under field conditions, and for comparing single-time capacitance data collected in areas with heterogeneous soil water status.

Quantification of canola root morphological traits under heat and drought stresses with electrical measurements

An understanding of the root traits in overcoming the constraints to canola growth imposed by heat and drought stresses is increasingly needed. This research examines the feasibility of using an electrical measurement method to screen canola root traits and its response to heat and drought stresses. Two genotypes were assessed under two temperature regimes (normal: 23/17 °C, vs. high: 27/24 °C, day/night) combined with three water levels in a controlled environment. All pots were subjected to root electrical capacitance (EC) and impedance (EI) measurements, followed by root morphological evaluation using a destructive method. Both heat and drought stresses suppressed root morphological parameters significantly, accompanied with a decreasing EC and increasing EI. Both 1 KHz and 10 KHz are acceptable current frequencies for effective measurement of EC and EI. A linear correlation was found between EC and most root parameters for canola plants grown in soil. This research illustrates the feasibility of using EC measurements to assess root morphological parameters of canola plants grown in soil. It is possible to apply this non–destructive method for studying the dynamics of roots subjected to abiotic stress. High EC can be associated with tolerance to heat and drought stresses.

Electrical capacitance as a predictor of root dry weight in shrub willow (Salix; Salicaceae) parents and progeny.

Premise of the study:Root biomass is an important trait often disregarded in woody perennial selection due to the challenge and expense of accurately and efficiently measuring large populations. In this study, we aim to develop a simple method that can predict root dry weight within a diverse shrub willow (Salix) breeding population representing species hybrids and their parents using root electrical capacitance (REC).Methods:The REC method was tested on plants started from cuttings and grown in pots with potting mix in the greenhouse for 11 wk to assess the relationship of REC with 24 biomass traits and its usefulness in allometric models for root and stem dry biomass.Results:Strong linear and positive correlations were found between REC and root dry biomass (r = 0.88). The total proportion of variance of root and stem dry biomass explained by predictors in multiple regression was 85% and 69%, respectively. The relative importance of predictor variables in allometric models was dominated by the contribution of REC.Discussion:This work provides an efficient and nondestructive technique to indirectly quantify root biomass of genetically diverse shrub willow progeny, which has great promise for selection of genotypes with varying root biomass and for the accurate estimation of belowground carbon sequestration.

Application of electrical capacitance measurement for in situ monitoring of competitive interactions between maize and weed plants

Applicability of root electrical capacitance (EC) measurement for monitoring of crop–weed competition was studied in a pot experiment. Maize (Zea mays L.) was grown both alone and with Echinochloa crus-galli or Abutilon theophrasti in different densities with regular measurement of root EC. Plants were harvested 42 days after planting to determine above- and belowground biomass. Depending on weed density, E. crus-galli-A. theophrasti interaction reduced the root EC of maize by 22–66% and 3–57%, respectively. Competitive effect of crop on weeds and intraspecific competition among weeds could also be detected by EC values: E. crus-galli was less sensitive both to the presence of maize and to intraspecific competition than A. theophrasti. Strong linear correlations between root dry mass and root EC for crop and weeds (with R2 from 0.901 to 0.956) were obtained by regression analyses at the end of the experiment. EC monitoring informed us on the emergence time of competition: E. crus-galli interfered with maize root growth a week earlier then A. theophrasti, and increasing weed densities accelerated the emergence of competition. In conclusion, the simple, non-destructive EC method should be considered a potential in situ technique for pot studies on crop–weed competition, which may partially substitute the intrusive techniques commonly used in agricultural researches.

Indirect monitoring of root activity in soybean cultivars under contrasting moisture regimes by measuring electrical capacitance

The applicability of root electrical capacitance (EC) measurement for in situ investigation of root activity and drought tolerance was tested in soybean cultivars. Well-watered and drought-stressed plants were grown in pots with repeated EC measurements, followed terminally by harvest to determine root dry mass (RDM), shoot dry mass (SDM), root/shoot ratio (RSR) and leaf area (LA). EC measurement showed the cultivar differences in root growth and biomass production. EC increased till the beginning of flowering, then became nearly constant. Terminal EC was highly correlated with RDM for non-stressed (R 2 = 0.844) and stressed plants (R 2 = 0.936). Drought reduced the EC of cultivars by 28.8–50.5 %, consistently with the corresponding changes of SDM (25.5–49.1 %) and LA (23.6–51.5 %), but considerably exceeded the loss of RDM (12.6–47.3 %) in some cultivars. The reason is drought increased the RSR (by 3.9–21.9 %), leading to decreased water uptake, and thus EC per unit of RDM. This was confirmed by the significantly decreased slope of EC–RDM regression line from 0.437 to 0.317 nF g−1 RDM calculated for well-watered and drought-stressed plants, respectively. As EC referred to root uptake activity, it was better indicator of the actual root status than RDM. EC measurement was adequate for monitoring the cultivar-specific differences in root growth and for estimation of biomass loss caused by drought. By supplementing the conventional methods, this in situ technique could be useful for various fields of agriculture, including cultivar selection or stress tolerance studies.

Modification of the tree root electrical capacitance method under laboratory conditions.

For many years, scientists have been searching for nondestructive methods for the measurement of plant root system parameters. The measurement of electrical capacitance (EC) across the root has been proposed as one such nondestructive method. This article presents a study on the determination of relationships between EC measurement and the shape and size of the electrodes immersed in medium that are used for measurement. Measurement of EC and the parameters characterizing root systems of 1-year-old seedlings of the common beech Fagus sylvatica L. was conducted under laboratory conditions. The measurements of EC were performed between seedling root systems and two different electrodes in the form of a cylinder or a rectangular plate. Statistically significant correlations were found between the capacitance and root system parameters in both the variants; however, the correlations were higher in the case of the flat rectangular plate. Correlation coefficient (r) between EC and total root length was 0.688 for cylindrical electrode and 0.802 for rectangular plate, for total root area 0.641 and 0.818, and for dry weight of root system 0.502 and 0.747. The best-fitted linear regression relationships between the EC and the measured parameters were characterized by low determination coefficients in variants with cylindrical electrodes, and higher with flat rectangular plate electrodes. The results indicated that a two-dielectric media concept is a better model than Dalton's model when attempting to interpret the behavior of root and soil capacitance. The different electrodes probably allow root capacitance measurements to be interpreted from different aspects. However, this hypothesis requires further verification.