Soil Water Content Conditions Research Articles

Soil moisture alters the responses of alpine ecosystem productivity to environmental factors, especially VPD, on the Qinghai-Tibetan Plateau

Water availability, which can be represented by soil water content (SWC), plays a crucial role in plant growth and productivity across the cold and arid Qinghai-Tibetan Plateau. However, the indirect effects of SWC are less well understood, and a more comprehensive understanding of its regulating effects may enhance the recognition of its importance, as this factor is pivotal for accurately predicting the future response of alpine ecosystems to climate change. In this study, in situ eddy covariance observation data from typical alpine ecosystems and satellite data covering the Qinghai-Tibetan region were used to comprehensively reveal the effects of SWC on ecosystem productivity. The results indicated that SWC played an important role in regulating the responses of gross primary productivity (GPP) to other environmental factors over both time and space, especially in terms of the responses of GPP to vapor pressure deficit (VPD). The regulating effect can be summarized as follows: there was a specific SWC value (SWC = 0.24 m3 m−3 on the Qinghai-Tibetan Plateau) above which SWC was no longer the primary limiting factor. The responses of GPP to certain environmental factors shifted from negative to positive when the SWC increased above this value. The responses of GPP to VPD exhibited the highest sensitivity to the regulating effects of SWC, with a general response pattern found across different temporal and spatial scales. The findings revealed divergent responses of GPP to environmental factors under different SWC conditions and between arid and humid regions, emphasizing the importance of soil water conditions. These findings suggest that water conditions should be given primary consideration in global change studies.

Evaluation of soil water content and bulk electrical conductivity across the U.S. Climate Reference Network using two electromagnetic sensors

AbstractSoil bulk electrical conductivity (BEC) was evaluated alongside soil volumetric water content (VWC) and soil temperature measurements using the HydraProbe (model HydraProbe, Stevens Water Monitoring Systems, Inc.) (hereafter called HP) with accuracy range of BEC ≤ 0.3 S m−1, and the time domain reflectometry (TDR)‐315L Probe (model TDR‐315L, Acclima, Inc.) (hereafter called AP) suitable for BEC up to 0.6 S m−1, at 23 stations of the U.S. Climate Reference Network. Previous evaluations revealed inconsistent performance of both sensors in some clay soils using manufacturer‐recommended calibrations in converting dielectric permittivity measurements to VWC. Here, we found that hourly values of BEC reached 0.6 S m−1 in high clay content soils and exceeded 2 S m−1 in high saline soils, and these high values of BEC were associated with poor performance and failures of both HP and AP sensors. Large values of BEC occurred in predominantly saturated soils where VWC values reached about 0.5 m3 m−3 for saline soils and about 0.7 m3 m−3 for clay soils, while low magnitudes of BEC were associated with low soil water content and seldomly saturated soils. Low hourly BEC values of less than 0.1 S m−1 were observed in wide variety of soil types, where sensor performance was typically excellent. The most influential factor on BEC was high soil water content conditions. Although dielectric permittivity measurements in estimating the soil water content were sensitive to BEC as some high clay content and high salinity soils increased BEC, the impact of large BEC on dielectric permittivity measurements was smaller in the well‐drained top soil layers than in deep soil layers that remained near saturation. Soil temperature had only a small impact on BEC. With high clay content and high salinity, the specific area of clay minerals was also associated with the magnitude of BEC.

Impact of years of grazing exclusion on surface soil temperature and hydrothermal relations in arid and semi‐arid grasslands

AbstractSoil temperature (Ts) and hydrothermal processes are determinants of grassland vegetation growth in arid and semi‐arid area. Implementation of grazing exclusion in grazed grasslands is bound to change the state of vegetation and soil, with consequent effects on Ts and hydrothermal relations. To investigate the differences in the response of Ts and hydrothermal variation to different durations of grazing exclusion, this study conducted a 4‐year fencing exclusion experiment from 2019 to 2022 in Eritu Ranch, Xilingole League, Inner Mongolia. Soil water content (SWC), Ts and precipitation were continuously observed under grazing and different years of grazing exclusion. Statistical correlation analysis was used to assess changes in Ts and moisture after 1 and 4 years of grazing exclusion, and to investigate the differences in Ts response to the same rainfall events and changes during freeze–thaw periods under different grazing exclusion durations. The results show that after 1 year of grazing exclusion, the summer surface Ts decreased by 0.23°C, while the winter surface Ts increased by 0.55°C. After 4 years of grazing exclusion, the summer surface Ts decreased further by 1.18°C, while the winter surface Ts decreased by 0.39°C. This suggests that grazing exclusion has differential effects on seasonal Ts dynamics. Compared with grazing grassland (GG), Ts in grazing exclusion grassland (GEG) shows less response to rainfall. During the freeze–thaw period, soil moisture in GEG is more sensitive to precipitation than in GG. Regression analysis revealed that the correlation between Ts and moisture during the freezing phase was weaker in GEG than in GG. Furthermore, the difference in correlation between 1 and 4 years of grazing exclusion was smaller than expected. During the melting phase, the relationship between Ts and SWC in the soil differed less after 1 year of grazing exclusion compared with GG. However, after 4 years of grazing exclusion, the correlation between Ts and SWC was generally greater in the GEG, suggesting that grazing exclusion may lead to changes in soil moisture dynamics that affect Ts. The results indicate that after 4 years of grazing exclusion, Ts and SWC conditions are better than those after 1 year of grazing exclusion. These findings have significant implications for understanding the impact of grazing‐induced soil warming and drying processes on ecosystems.

Divergent impacts of VPD and SWC on ecosystem carbon-water coupling under different dryness conditions

Ecosystem water use efficiency (WUE) is an indicator of carbon-water interactions and is defined as the ratio of gross primary productivity (GPP) to evapotranspiration (ET). However, it is currently unclear how WUE responds to atmospheric and soil drought events in terrestrial ecosystems with different dryness conditions. Additionally, the contributions of GPP and ET to the WUE response remain poorly understood. Based on measurements from 26 flux tower sites distributed worldwide, the binning method and random forest model were employed to separate the sensitivities of daily ecosystem WUE, GPP, and ET to vapor pressure deficit (VPD) and soil water content (SWC) under different dryness conditions (dryness index = potential evapotranspiration/precipitation, DI). Results showed that the sensitivity of WUE to VPD was negative at humid sites (DI < 1), while the sensitivity of WUE to SWC was positive at arid sites (DI > 2). Furthermore, the contribution of GPP to VPD-induced WUE variability was 63 % at humid sites, and the contribution of ET to SWC-induced WUE variability was 68 % when SWC was less than the 60th percentile at arid sites. Consequently, one increasing VPD-induced decrease in GPP was generally linked to a decrease in WUE at humid sites, and one drying soil moisture-caused decrease in ET was linked to a WUE increase under low SWC conditions at arid sites. Finally, VPD had a stronger effect on WUE than SWC when VPD was less than the 90th percentile or SWC was greater than the 50th percentile. Our findings underscore the importance of considering ecosystem dryness when investigating the impacts of VPD and SWC on ecosystem carbon-water coupling.

Estimating ecosystem evaporation and transpiration using a soil moisture coupled two-source energy balance model across FLUXNET sites

The two-source energy balance model coupled with soil moisture (TSEB-SM) was evaluated against observations from a global set of 57 eddy covariance (EC) sites, part of the FLUXNET2015 dataset. In addition, modeled soil evaporation (E) and transpiration (T) were compared with the values obtained from the Transpiration Estimation Algorithm (TEA) and underlying water use efficiency (uWUE) approaches. The TSEB-SM model framework using near-surface soil moisture improved the agreement to EC-observed sensible and latent heat fluxes, reducing mean absolute percentage error (MAPE) by about 30% and root mean square error (RMSE) by about 44 W/m2 across all sites. The results show that the advantage of the TSEB-SM model, with respect to the original TSEB, becomes more evident as the ratio of actual to potential evapotranspiration (AET/PET) decreases. The E and T produced by TSEB-SM has better correlation with the results of uWUE partitioning than TSEB, especially under low soil water content condition. Likewise, TSEB-SM is superior to TSEB in simulating T when compared with sap flow measurements derived from the SAPFLUXNET database. These results imply that the development and application of TSEB-SM has made significant advances in modeling surface water fluxes, even though uncertainties remain. The approach used in TSEB-SM, driving the model with an extensive remotely sensed parameter set, gives valuable information on water use and provides an alternative to Global Climate Models where complex interactions of ecosystems are parametrized. Thus, TSEB-SM provides a unique insight into the flow of energy and the role of surface fluxes in the global water cycle.

Three Bayesian Tracer Models: Which Is Better for Determining Sources of Root Water Uptake Based on Stable Isotopes under Various Soil Water Conditions?

Stable hydrogen and oxygen isotopes provide a powerful technique for quantifying the proportion of root water uptake (RWU) from different potential water sources. Although many models coupled with stable isotopes have been developed to estimate plant water source apportionment, inter-comparisons of different methods are still limited, especially their performance under different soil water content (SWC) conditions. In this study, three Bayesian tracer mixing models, which included MixSIAR, MixSIR and SIAR, were tested to evaluate their performances in determining the RWU of winter wheat under various SWC conditions (normal, dry and wet) in the North China Plain (NCP). The proportions of RWU in different soil layers showed significant differences (p &lt; 0.05) among the three Bayesian models, for example, the proportion of 0–20 cm soil layer calculated by MixSIR, MixSIAR and SIAR was 69.7%, 50.1% and 48.3% for the third sampling under the dry condition (p &lt; 0.05), respectively. Furthermore, the average proportion of the 0–20 cm layer under the dry condition was lower than that under normal and wet conditions, being 45.7%, 58.3% and 59.5%, respectively. No significant difference (p &gt; 0.05) was found in the main RWU depth (i.e., 0–20 cm) among the three models, except for individual sampling periods. The performance of three models in determining plant water source allocation varied with SWC conditions: the performance indicators such as coefficient of determination (R2) and Nash-Sutcliffe efficiency coefficient (NS) in MixSIAR were higher than that in MixSIR and SIAR, showing that MixSIAR performed well under normal and wet conditions. The rank of performance under the dry condition was MixSIR, MixSIAR, and then SIAR. Overall, MixSIAR performed relatively better than other models in predicting RWU under the three different soil moisture conditions.

Early warning index of flash flood disaster: a case study of Shuyuan watershed in Qufu City.

Flash flood disaster is one of the important natural disasters, bringing harm to human life and causing serious economic losses, so it is urgent to improve the accuracy of flash flood warning. To determine the critical rainfall and early warning indicators of disaster prevention objects, the Shuyuan Watershed of Qufu City Shandong Province was selected as the research object, the key disaster prevention objects were screened and finally, Hengmiao Village and Gaolou Village were selected as typical disaster prevention objects. Empirical analysis method, Storm analysis method, and model analysis method were used to calculate the critical rainfall at different times under different soil water content conditions, compare and analyze the rationality and existing problems of these three methods, and comprehensively determine the indicators of typical disaster prevention objects under different circumstances. The results show that the value of the index calculated by the storm analysis method is small and calculated by the model analysis method is large. This paper can improve the accuracy of flash flood warning, select the critical rainfall calculation method according to local conditions, accurately calculate the parameter values, and deal with the problem of effective early warning in the region as a whole.

PENENTUAN PEMETAAN KADAR AIR TANAH OPTIMAL PADA LAHAN PERKEBUNAN KELAPA SAWIT (STUDI KASUS: KEBUN CIKASUNGKA, PT PERKEBUNAN NUSANTARA VIII, CIMULANG, BOGOR)

Soil water content is one of the dynamics of water conditions that can be a limiting factor in achieving optimal oil palm productivity. The extensive oil palm plantations make it difficult to acquire soil moisture content data. Soil water content conditions can be estimated by remote sensing technology through the vegetation and drought index, and also can be mapped using an interpolation approach. This study aimed to map the optimal soil water content in oil palm plantations based on Normalized Difference Vegetation Index (NDVI), Normalized Multi-band Drought Index (NMDI), and Interpolation. The results showed that the highest soil moisture was found on 0-3% slope gradient and the lowest on 8-15% slope gradient. Vegetation density based on NDVI analysis result was quite high, while the level of dryness based on NMDI analysis result was quite humid. Mapping of soil water content based on NDVI and NMDI had a very weak correlation with soil water content so both indices are less responsive in describing soil moisture conditions in the field. Interpolated water content value had a fairly strong relationship with the soil water content and had the highest suitability, so the interpolation approach can be recommended for mapping soil water content in an oil palm plantation area.

LAI and biomass of kenaf as affected by sowing time and plant density: A simple model simulates the time course in a Mediterranean environment

Kenaf (Hibiscus cannabinus L.) is a warm-season annual plant grown in the past for the bast fiber. In the last decades, this crop has been re-evaluated for many alternative industrial uses of its biomass (i.e., production of biofuel, biocomposite materials, bioproducts). In this paper, the interaction effects of sowing time (May and June) and plant population (P20 and P40, 20 and 40 plants m-2, respectively) on yield and some biomass parameters were analysed in two cultivars of kenaf (Tainung 2-TAI, and Everglades 41-EVER), in a two-year experiment in semi-arid environment, under irrigation. The aim of this paper was to assess the potential of this crop as an energy or industrial feedstock, in south Mediterranean environment where was never cultivated.Overall, plants from late sowing (June) were smaller and with less node, those at high plant density (P40) were thinner. In both seasons, plants of TAI were taller than those of EVER. Plant weight was greater in P20, and an overall significant negative correlation was found between plant weight and actual plant density (r = −0.76 **). The shift of sowing time reduced significantly the final dry biomass. Crop productivity did not change with plant density, however a higher percent bark corresponded to P40 in both years, cultivars, and sowing times, A simple model was developed to simulate and predict the course of LAI and dry biomass (AGB) with time, using field dataset of 2004, for calibration, and dataset of 2005, for validation. The minor response of LAI to plant population in 2005 led to a low accuracy of model approximation. This result suggests that other variables that are not considered in the model, may influence LAI. Nevertheless, the overall AGB model approximation of observed value was accurate. Concluding, the results revealed that biomass productivity is more influenced by sowing time than by plant density. However, plant population has been found to regulate the proportion of bark/core layers, with important implications for industrial (energy and pulp production) purposes. Further improvements on the simple model developed, e.g., including soil water nitrogen balances submodels, may be done, in order to explore the possibility of using the model under different conditions of soil water content and nitrogen fertilization.

Analysis on the relationship between sun-induced chlorophyll fluorescence and gross primary productivity of winter wheat in northern China

The sun-induced chlorophyll fluorescence (SIF) is directly related to the photosynthesis of winter wheat and has a good linear relationship with the gross primary production (GPP). However, the relationship of SIF and GPP is still uncertain under different soil water content conditions. The sun-induced chlorophyll fluorescence, GPP and non-photochemical quenching (NPQ) are the three ways of photosynthetically active radiation in plants. The photochemical reflectance index (PRI) can be used as a proxy indicator of NPQ to characterize the change in heat dissipation during photosynthesis process of winter wheat. To detect the impact of soil water content on winter wheat photosynthesis and SIF and GPP relationship, based on the ground measurement data at Zhaoxian Experimental Station in northern China during the growing season in 2018 and the simulated data by the SCOPE model, we use PRI to improve the GPP model estimated by SIF. The results indicate that: (1) PRI is sensitive to soil water content (R2 = 0.64), so it can be used to improve the estimation of GPP based on SIF under different soil water conditions; (2) For the ground measurement data, PRIobv can improve the estimation accuracy of GPPobv by SIFobv. Under different soil water content (SWC) conditions, the relationship between GPPobv and SIFobv is significantly correlated (R2 = 0.33–0.45, p < 0.01), and PRIobv can be used to improve the estimation between GPPobv and SIFobv (R2 = 0.57–0.62, p < 0.01); (3) The simulation results of the SCOPE model show that the simulation effect of the model can be better optimized by adding PRI under the condition of relatively dry soil (△R2 = 0.13–0.17). Our research suggests that PRI can be added when estimating GPP using SIF information, especially when winter wheat is under low soil water content conditions.

Evaluation of method to model stomatal conductance and its use to assess biomass increase in poplar trees

Stomatal conductance (gs) is the main limiting factor for photosynthesis and is sensitive to plant water status. Accurately assessing the behavior of gs under water deficit stress is essential to model plants carbon and water flux, which govern vegetation biomass production and dynamics. However, direct measurement of gs with gas exchange analyzer can be time-consuming and laborious, especially under field conditions, thus constraining the data availability for validating the modeling outcome. This difficulty can be solved if measurement of gs is automated. Here, we report on dynamics of gs and the maximum (gsmax) of Populus tomentosa, derived from automatically recorded meteorological variables and sap flux density (Js) and turgor pressure sensors outputs (Z) measured in three P. tomentosa trees from a short-rotation plantation subjected to different water stress levels along a whole growing season. The simulated gsmax was related to aboveground (ABM) and underground biomass (UBM) increase by leaf area. Js and Z were continuously measured using sap flow and ZIM sensors. Our results showed that the sensitivity of Js to air vapor deficit (D) (i.e. Js/D) correlated well with gs, and the sensitivity of Z to D (i.e. dZ/dD) was well coupled with gsmax. In addition, the ABM increase was linearly aligned with simulated gsmax multiplied by leaf area (LA) (R2 > 0.7). Also, increment in UBM was significantly correlated with simulated gsmax * LA across all observed trees, being the best described by a logistic function (R2 > 0.7). We conclude that gs can be well simulated through automatic monitoring of Js and Z for different meteorological and soil water content conditions. Moreover, the simulated gsmax was also closely related to biomass production both above and underground, which opens the possibility for using it to manage irrigation in smart agriculture and forestry in the future.

Toprak Su İçeriğinin Belirlenmesinde PR2’nin Performansının Değerlendirilmesi

As it is known, drought is one of the most important issues of recent years. On the other hand, agriculture is the sector that uses the most water. The impact of drought can be reduced by reducing the water used in agriculture. Therefore, it is very important to determine the application time and amount of irrigation water for a successful agricultural irrigation management. One of the most important ways to achieve this success is to accurately determine and monitor the water content in the plant root zone. Soil water content can be determined in two ways; direct and indirect methods. The direct measurement method is tedious, laborious and time consuming. Instead, a large number of indirect measurement methods are developed. One of these indirect measurement methods is the PR2 Profile Probe method. In this study, the possibilities of using PR2 method under different soil water content conditions were investigated. First, the calibration of the PR2 method was made within 40 cm of soil depth. Then, the water content in the soil was monitored by the PR2 method under three different soil water content (100%, 75% and 50%) conditions. R2 values for calibration relationships varied between 0.7947 and 0.9305. In the study, it was concluded that soil water content could be monitored with PR2 Profile Probe.

Effect of potassium application on morphophysiological two varieties of soybean under drought stress

Domestic soybean production is getting weaker due to drought stress which affects all aspects of plant growth and metabolism, besides using adaptive plant varieties, increasing plant nutrition, especially potassium, also affects increasing plant tolerance to drought. The research aimed to examine the effect of potassium application on the morphophysiological of two varieties of soybean under drought stress. The research was conducted in a plastic house, Deli Serdang Regency, North Sumatra, using a randomized block design with three factors. The first factor was soil water content condition, which consisted of 80% and 40% field capacity. The second factor was variety, consisted of Grobogan and Dering-1. The third factor was the application of potassium, consisted of without potassium 100, 200, 300 kg KCL ha−1. Result showed that drought stress decreased potassium uptake, the relative water content (RWC) of leaf and plant height. Grobogan variety more adaptive to drought stress with the highest plant height (71.49 cm), K content (1.77%), K uptake (43.85 mg/plant), and leaf RWC (37.91%). Application of K at a dose of 200 kg ha−1was the most appropriate to encourage the growth of soybean plants under drought stress with the highest total K (1.76%) and leaf RWC (44.40 mg/plant).

Electrical resistivity imaging for monitoring soil water motion patterns under different drip irrigation scenarios

The use of hydrogeophysical methods provides insights for supporting optimal irrigation design and management. In the present study, the electrical resistivity imaging (ERI) was applied for monitoring the soil water motion patterns resulting from the adoption of water deficit scenarios in a micro-irrigated orange orchard (Eastern Sicily, Italy). The relationship of ERI with independent ancillary data of soil water content (SWC), plant transpiration (T) and in situ measurements of hydraulic conductivity at saturation (Ks, i.e., using the falling head method, FH) was evaluated. The soil water motion patterns and the maximum wet depths in the soil profile identified by ERI were quite dependent on SWC (R2 = 0.79 and 0.82, respectively). Moreover, ERI was able to detect T in the severe deficit irrigation treatment (electrical resistivity increases of about 20%), whereas this phenomenon was masked at higher SWC conditions. Ks rates derived from ERI and FH approaches revealed different patterns and magnitudes among the irrigation treatments, as consequence of their different measurement scales and the methodological specificity. Finally, ERI has been proved suitable for identifying the soil wetting/drying patterns and the geometrical characteristics of wet bulbs, which represent some of the most influential variables for the optimal design and management of micro-irrigation systems.

Creeping bentgrass summer decline as influenced by climatic conditions and cultural practices

AbstractDespite its popularity as a putting surface in North Carolina, creeping bentgrass (Agrostsis stolonifera L.) is highly susceptible to summer bentgrass decline (SBD) during hot summer months. Cultural practices have been shown to help alleviate the pressure of SBD. The objectives of this study were to detail the impacts of N fertility, soil water content, and hollow‐ and solid‐tine cultivation on creeping bentgrass quality. Cultural treatments included four N rates (97, 195, 293, and 391 kg ha−1 yr−1), four hollow‐tine core cultivation programs (6.4 mm diam. tines two times yr−1, 9.5 mm diam. tines two and three times yr−1, and a non‐cored control), two soil water content levels (low and high), and two summer solid‐tine spiking cultivation treatments (spiked and not spiked). Visual turfgrass quality was measured. A N rate greater than 195 kg ha−1 was needed to maintain acceptable turfgrass quality. High soil water content consistently provided better summer turfgrass quality compared to low soil water content conditions. Nitrogen fertility and soil water content interacted where higher levels of both resulted in the best quality ratings. Hollow‐core cultivation reduced turfgrass quality at the lower N rates; whereas, solid‐tine spiking had no effect on turfgrass quality. Although weather plays a large role in SBD in North Carolina, results from this study show that cultural practices can influence its severity.

Evapotranspiration and crop coefficients from lysimeter measurements for sprinkler-irrigated canola

Canola is a water-stress tolerant crop, which could be an alternative in areas with limited water resources. However, in arid and semi-arid environments where rainfall events are scarce and increasingly erratic, the use of irrigation is necessary for canola production to reach its maximum yield. The goal of this study was to determine the crop evapotranspiration (ETc) and crop coefficients of sprinkler irrigated canola (Brassica napus L.) under non-limiting soil water content conditions. A 2-year field experiment was conducted in the lysimeter facility located in Albacete (SE Spain). A large weighing lysimeter (2.7 × 2.3 × 1.7 m), with an accuracy of 0.04 mm equivalent water depth, was used to measure the daily crop evapotranspiration (ETc) rate throughout two growing seasons. ETc values were determined using daily mass change in the lysimeter. Cumulative ETc was replaced in the lysimeter through sprinkler irrigation applications, thus crop water stress was avoided. Seasonal lysimeter based (measured) canola ETc was 472 and 602 mm in 2008 and 2012, respectively. The 28 % higher ETc value in 2012 was mainly due to a much higher evaporative demand during the crop growth mid-season period of 2012. The Kc values were determined using grass reference evapotranspiration (ETo) calculated with the FAO56 Penman-Monteith equation and the ETc calculations from the lysimeter data. The dual crop coefficient approach was used to separate crop transpiration (Kcb) from soil evaporation (Ke). For the two canola seasons, mid-season Kc and Kcb values, after FAO56 climate adjustment, were Kc mid (std) = 1.15 and Kcb mid (std) = 1.11. Those values were reached coinciding with maximum fraction of ground cover (fc) values of up 0.95 and 0.97 for 2008 and 2012, respectively. The seasonal evaporation component for sprinkler-irrigated canola was estimated to be about 24 % and 19 % of ETc in 2008 and 2012, respectively. The good linear relationship found between canola Kcb values and fc and the excellent agreement found between remotely sensed vegetation indices (VIs) and different biophysical parameters, such as Kcb and fc, will allow monitoring and estimating the spatially distributed water requirements of canola at field and regional scales using multispectral satellite imagery.

Nutritional status of ‘Hass’ and ‘Fuerte’ avocado (Persea americana Mill.) plants subjected to high soil moisture

In this study, the effect of increased soil moisture on the nutritional status of two key commercial avocado (Persea americana Μill.) cultivars, ‘Fuerte’ and ‘Hass’, was examined. The results revealed that prolonged exposure of plants to high soil water content conditions (waterlogging) reduced the total nutrient content (absolute quantity) of almost all of the nutrients in scion’s tissues (leaves and stems) of both cultivars. The decrease of nutrient content in the ‘Fuerte’ leaves was more prominent/severe compared to the ‘Hass’ leaves, which could be the outcome of the reported higher sensitivity of the cultivar to soil waterlogged conditions in previous studies. Interestingly, the inability of ‘Fuerte’ avocado plants to withstand high soil moisture conditions was not reflected in the relative concentrations of most nutrients, both in leaves and stems. Indeed, significantly higher concentrations of P, K, B, Fe, and Zn were found in the leaves of ‘Fuerte’ waterlogged plants than in well-watered ones. This fact reveals that under marginal/stressful conditions, like waterlogging, nutrient concentration in tissues does not reflect potential negative effects on total nutrient uptake of avocado plants, obviously due to concentrated nutrient phenomena primarily created by the stress-dependent growth inhibition. Therefore, total nutrient content is proposed as a more representative indicator for assessing plant response to waterlogged conditions.

Use of VIS-NIR-SWIR spectroscopy for the prediction of water status in soybean plants in the Colombian Piedmont Plains

Water stress due to soil water deficit is one of the limitations in the soybean production, which can be detected with multivariate statistical analysis and spectral reflectance signals, in the visible and near infrared range. This work was conducted to determine a spectral pattern during the stages of plant development from three conditions of soil water content. Cross validation was used for validation of the classification model, with an accuracy of 82.5%, and the model reached a mean of 82 and 90% of sensitivity and specificity, respectively, at the phenological state of pod filling. The regions with the highest correlation between factors and wavelengths were located at 400-600 nm and 1850-2100 nm, which are related with the peaks of water energy absorbance associated to the hydric state of the plant

Effects of Biochar Application and Ageing on the Adsorption of Antibiotics in Purple Soil

Effects of biochar application (at rates of 0%, 1%, and 5%) and field ageing (for 1 a) on the sorption of three antibiotics (sulfadiazine, sulfamethazine, and florfenicol) were studied by batch equilibrium tests for a calcareous purple soil of sloping cropland, which is widely distributed in hilly areas of the upper Yangtze River. A soil-water ratio of 1 g:1 mL, which was close to the actual field soil water content condition, was adopted in the experiment, and comparisons were made to the commonly used ratio of 1 g:10 mL. The results showed that adsorption isotherm data of the studied antibiotics were fitted well by the linear and Freundlich model, and the free energy (ΔGθ) ranged from -0.39 to 11.53 kJ·mol-1, thus indicating that the adsorption of the three antibiotics on the control soils and biochar amended soils was mainly physical adsorption. Application of fresh biochar was found to markedly enhance the adsorption of antibiotics, especially for sulfamethazine and florfenicol of low Kow values, while such an effect was strongly weakened after ageing. The fluorescence peak response intensity of the adsorption equilibrium solution of the aged biochar amended soil was lower than that of the fresh biochar amended soil, so the difference in adsorption performance between fresh and aged biochar amended soils may have been due to the decrease of unstable and soluble organic matter in the latter's biochar after aging.

Transpiration dynamics and water sources for selected indigenous trees under varying soil water content

The major route through which water from the earth’s surface re-enters the hydrologic cycle in forested ecosystems is via tree transpiration (T). It is therefore important to have detailed understanding of the quantity and source of water transpired by different tree species. The aims of this study were to i) assess the trends of T for selected tree species (camel thorn, sweet thorn, shepherd’s tree and buffalo thorn) across a range of soil water content conditions and ii) partition the total T of the selected tree species growing in arid environments dominated by open cast mining activities into soil water and groundwater. Tree T was measured using the compensation heat pulse velocity (CHPV) method, while soil water content was monitored using DFM capacitance probes. The soil water content within the upper 50 cm soil profile ranged from 11 mm during the dry season to 20 mm during the wet season. The deeper soil layer (50–120 cm) was generally wetter compared to the top layer with water content was up to >30 mm during the wet season. The measured tree T ranged from 0.2 mm day−1 on buffalo thorn during the dry season to 1.9 mm day−1 on sheperd’s tree in summer. It was also revealed that T of large (diameter at breast height =46 cm) camel thorn trees is not responsive to seasonal variations of soil water availability and remained constant at approximately 1.2 mm day−1. Diurnal patterns of T did not effect changes on the soil water depletions within the top 120 cm soil profile, which indicated that the trees sourced water beyond this zone. Signs of daytime redistribution were observed within the canopy areas of the investigated trees during very limited soil water conditions of the dry season. It was concluded that the water use of trees is inclined to the seasonal variations, which however is not the case in old trees. Close to 100% of the water transpired by trees in the study area is sourced below 1.2 m (vadose zone and water table). We recommended investigation of daytime redistribution among the indigenous tree species of the study area. We also recommended extension of tree water use studies to other species for comprehensive catchment tree water use calculations to inform water budgets.