Available Water Capacity Research Articles

The role of biochar particle size and application rate in promoting the hydraulic and physical properties of sandy desert soil

Enhancing the resistance of sandy desert soil to drought and wind erosion is key to controlling aeolian desertification. Using biochar as an amendment can improve soil quality. This study aimed to determine the impacts of biochar particle size and application rate on the hydraulic and physical properties of sandy desert soil. Biochars were produced by pyrolyzing corn straw at 500 °C with limited oxygen. Samples of sandy desert soil were collected from the Tengger Desert in Northwestern China. Tests were designed with three biochar particle sizes (0–0.25, 0.25–1, and 1–2 mm) and five biochar application rates (wt%: 0, 0.5%, 1%, 2%, and 4%). Soil hydraulic and physical properties were characterized by the soil–water characteristic curve, soil porosity, soil specific surface area (SSA), and soil structural index (SI). The results showed that biochar significantly increased the soil porosity and the number of extreme micropores, micropores, and small pores. As a consequence, the saturated soil water content (θs), permanent wilting point (PWP), field capacity (FC), and available water content (AWC) were significantly enhanced. The significant improvement in SI demonstrated that biochar enhanced the soil aggregate stability, therefore, the resistance of sandy desert soil to wind erosion is enhanced. Biochar dosage was a more important factor that influenced the FC, AWC, PWP, SI, and SSA of the soil more than biochar particle size. The properties of θs, PWP, FC, AWC, and SI were all closely related to SSA, indicating that SSA played a key role in the mechanism affecting the response of the soil to biochar application. The significant increase in water retention and aggregate stability of sandy desert soil with added biochar suggests a novel strategy to control aeolian desertification by amending the soil.

A Comparative Analysis of Root Growth Modules in HYDRUS for SWC of Rice under Deficit Drip Irrigation

Root distribution during rice cultivation is a governing factor that considerably affects soil water content (SWC) and root water uptake (RWU). In this study, the effects of activating root growth (using growth function) and assigning a constant average root depth (no growth during simulation) on SWC and RWU for rice cultivation under four deficit drip irrigation treatments (T90, T80, T70, and T60) were compared in the HYDRUS-2D/3D model version 3.03. A secondary objective was to investigate the effect of applied deficit irrigation treatments on grain yield, irrigation water use efficiency (IWUE), and growth traits of rice. The simulated DI system was designed to reflect a representative field experiment implemented in El-Fayoum Governorate, Egypt, during two successive seasons during 2017 and 2018. The deficit treatments (T90, T80, T70, and T60) used in the current study represent scenarios at which the first irrigation event was applied when the pre-irrigation average SWC within the upper 60 cm of soil depth was equal to 90%, 80%, 70%, and 60% of plant-available water, respectively. Simulation results showed that as water deficiency increased, SWC in the simulation domain decreased, and thereby, RWU decreased. The average SWC within the root zone during rice-growing season under different deficit treatments was slightly higher when activating root growth function than when considering constant average root depth. Cumulative RWU fluxes for the case of no growth were slightly higher than for the case of root growth function for T90, T80, and T70 accounting for 1289.50, 1179.30, and 1073.10 cm2, respectively. Average SWC during the growth season (24 h after the first irrigation event, mid-season, and 24 h after the last irrigation event) between the two cases of root growth was strongly correlated for T90, T80, T70, and T60, where r2 equaled 0.918, 0.902, 0.892, and 0.876, respectively. ANOVA test showed that there was no significant difference for SWC between treatments for the case of assigning root growth function while the difference in SWC among treatments was significant for the case of the constant average root depth, where p-values equaled 0.0893 and 0.0433, respectively. Experimental results showed that as water deficiency decreased, IWUE increased. IWUE equaled 1.65, 1.58, 1.31, and 1.21 kg m−3 for T90, T80, T70, and T60, respectively. Moreover, higher grain yield and growth traits of rice (plant height, tillers number plant−1, panicles length, panicle weight, and grain number panicles−1) were obtained corresponding to T90 as compared with other treatments. Activating the root growth module in HYDRUS simulations can lead to more precise simulation results for specific dates within different growth stages. Therefore, the root growth module is a powerful tool for accurately investigating the change in SWC during simulation. Users of older versions of HYDRUS-2D/3D (version 2.05 and earlier) should consider the limitations of these versions for irrigation scheduling.

PERAN EMBUNG TERHADAP INDEKS PERTANAMAN PADI DAN FAKTOR YANG MEMPENGARUHI PRODUKSI PADI (STUDI KASUS LOKASI EMBUNG KABUPATEN BOGOR, JAWA BARAT)

Rice production in Bogor Regency has fluctuated and tends to fall, even though almost 70-80% of technical irrigated land with rainfall is relatively stable per year and higher than its surroundings, but the availability of water for rice plants is unstable. This research aimed to analyze the difference in Planting Index (IP) before and after embung in the research location and the role of the reservoir factor in increasing rice production in the research location. This research was approached using quantitative descriptive in a case study at the Embung location, Bogor Regency. Furthermore, the difference between the planting index (IP) of rice before and after embung was examined with the non-parametric Wilcoxon signed-rank test to determine there is a role for embung factor in increasing rice production using multiple linear regression analysis (F test and t-test). The result showed that there is a significant difference in the Planting Index (IP) before and after embung at the research location based on the non-parametric Wilcoxon signed-rank test, with the Asymp value. Sig 0.009 <0.05 (α = 0.5%) or the level of confidence 95%, then there is a role for embung variable factor on the increase in production at the research location based on multiple linear regression analysis, either simultaneously (F test) or partially (t-test). significant to the rice production variable with a significance value less than 0.05 (α = 0.5%) or a confidence level of 95%.

Machine Learning With GA Optimization to Model the Agricultural Soil-Landscape of Germany: An Approach Involving Soil Functional Types With Their Multivariate Parameter Distributions Along the Depth Profile

Societal demands on soil functionality in agricultural soil-landscapes are confronted with yield losses and environmental impact. Soil functional information at national scale is required to address these challenges. On behalf of the well-known theory that soils and their site-specific characteristics are the product of the interaction of the soil-forming factors, pedometricians seek to model the soil-landscape relationship using machine learning. Following the rationale that similarity in soils is reflected by similarity in landscape characteristics, we defined soil functional types (SFTs) which were projected into space by machine learning. Each SFT is described by a multivariate soil parameter distribution along its depth profile. SFTs were derived by employing multivariate similarity analysis on the dataset of the Agricultural Soil Inventory. Soil profiles were compared on behalf of differing sets of soil properties considering the top 100 and 200 cm, respectively. Various depth weighting coefficients were tested to attribute topsoil properties higher importance. Support vector machine (SVM) models were then trained employing optimization with a distributed multiple-population hybrid Genetic algorithm for parameter tuning. Model training, tuning, and evaluation were implemented in a nested k-fold cross-validation approach to avoid overfitting. With regards to the SFTs, organic soils were differentiated from mineral soils of various particle size distributions being partly influenced by waterlogging and groundwater. Further SFTs reflect soils with a depth limitation within the top 100 cm and high stone content. Altogether, with SVM predictive model accuracies between 0.7 and 0.9, the agricultural soil-landscape of Germany was represented with eight SFTs. Soil functionality with regards to the soil’s capacity to store plant-available water and soil organic carbon is well characterized. Four additional soil functions are described to a certain extent. An extension of the approach to fully cover soil functions such as nutrient cycling, agricultural biomass production, filtering of contaminants, and soil as a habitat for soil biota is possible with the inclusion of additional soil properties. Altogether, the developed data product represents the 3D multivariate soil parameter space. Its agglomerated simplicity into a limited number of spatially allocated process units provides the basis to run agricultural process models at national scale (Germany).

Changes in soil water retention and content during shrub encroachment process in Inner Mongolia, northern China

Soil water retention is the link between hydrologic processes and ecological patterns, and is one of the vital hydrological properties of soils. However, the influence of shrub encroachment on soil water retention and content remains unclear, and the factors influencing soil water retention and content are also not well understood. Therefore, this study aims to investigate the changes in soil water retention and content during the shrub encroachment process and to reveal their influencing factors. In this study, three states of shrub encroachment were identified according to the percentage of shrub cover. Soil samples of the shrub patches and adjacent interspace grass patches were collected in each state of shrub encroachment. The soil water retention curves of the samples were generated, and the soil water contents of the samples were measured. The results showed that the field capacity (FC) and plant-available water capacity (PAWC) of both shrub patches and interspace grass patches increased during shrub encroachment, which suggests that shrub encroachment has positive effects on soil water retention. The FC and PAWC of the shrub patches were 14.7% and 14.5% higher than those of the interspace grass patches, respectively. The shrub patches were also characterized by higher soil water content and storage than the interspace grass patches. Shrub roots, soil organic matter, and clay content were the three most crucial factors positively affecting soil water retention and content during shrub encroachment process. This study can further our understanding of the ecohydrological effects of shrub encroachment in arid and semiarid grasslands and facilitate related modeling studies.

Water availability regulates tree mixture effects on total and heterotrophic soil respiration: A three‐year field experiment

Soil respiration is of critical importance to the energy balance and element cycling of terrestrial ecosystems. Biodiversity loss and changes in rainfall regimes are predicted to increase, and in so doing have the potential to affect soil C cycling. However, uncertainties remain concerning the effects of tree diversity on soil respiration, and how these effects might be modified by altered water availability. Here, we measured the total soil respiration (RS) and heterotrophic respiration (RH) rates during the 2017 to 2019 growing seasons in stands dominated by Populus tremuloides, Pinus banksiana, and their relatively even mixtures under reduced (−25% throughfall), ambient, and added (+25% throughfall) precipitation in a boreal forest of Central Canada. We found that the RS and RH were 28% and 26% greater, respectively, in the mixtures than expected from those of monocultures that received ambient water availability, while the RH/RS were unaffected by tree mixtures. On average, the addition of water increased Rs and RH by 19%, and 10%, respectively, with more pronounced increases of Rs in tree mixtures, which resulted in 55% higher Rs in mixtures relative to monocultures. In contrast, water reduction did not affect the Rs but decreased RH in mixtures. Additionally, the effects of mixtures on RH increased over the three-year duration of the experiments. Both the Rs and RH decreased, while the RH/Rs increased with higher soil fungal to bacterial ratios. Our results revealed that plant species mixtures and water availability interactively influenced soil respiration under natural conditions. We provided novel experimental insights, which indicated that the establishment of diverse forests can increase soil C cycling over time, particularly under increased water availability.

Temporal Aspect of the Terrestrial Invertebrate Response to Moisture Dynamic in Technosols formed after Reclamation at a Post-Mining Site in Ukrainian Steppe Drylands

Abstract Different approaches were applied to assess soil moisture optima and tolerance of the ecological niche temporal projection of terrestrial invertebrates within an experimental polygon created to investigate the reclamation processes after deep underground hard-rock mining in the Ukrainian steppe drylands. Sampling was carried out in 2013–2015 on a variant of artificial soil (technosols). To investigate the spatiotemporal variation in the abundance, species richness and species composition of invertebrate assemblages the animals were sampled using pitfall traps. The readily available water for plants, precipitation, wind speed, atmospheric temperature, atmospheric humidity, and atmospheric pressure were used as environmental predictors. The two-dimension geographic coordinates of the sampling locations were used to generate a set of orthogonal eigenvector-based spatial variables. Time series of sampling dates were used to generate a set of orthogonal eigenvector-based temporal variables. Weighted averaging, generalized linear mixed models, Huisman-Olff-Fresco models expanded by Jansen-Oksanen, correspondence analysis, and constrained correspondence analysis were used to estimate soil moisture species optima and tolerance. The moisture content in the technosols was revealed to be the most important factor determining the temporal dynamics of terrestrial invertebrate community in conditions of semi-arid climate and the ecosystem which formed as a result of the reclamation process. The species response to the soil water content is affected not only by the soil water content but also by the complex of the other environmental, temporal, and spatial factors. The effect of other factors on the species response must be extracted previously to find real estimations of the species optima and tolerance.

Estimation of Bare Soil Moisture from Remote Sensing Indices in the 0.4–2.5 mm Spectral Range

Abstract Soil moisture content (SMC) is an important element of the environment, influencing water availability for plants and atmospheric parameters, and its monitoring is important for predicting floods or droughts and for weather and climate modeling. Optical methods for measuring soil moisture use spectral reflection analysis in the 350–2500 nm range. Remote sensing is considered to be an effective tool for monitoring soil parameters over large areas and to be more cost effective than in situ measurements. The aim of this study was to assess the SMC of bare soil on the basis of hyperspectral data from the ASD FieldSpec 4 Hi-Res field spectrometer by determining remote sensing indices and visualization based on multispectral data obtained from UAVs. Remote sensing measurements were validated on the basis of field humidity measurements with the HH2 Moisture Meter and ML3 ThetaProbe Soil Moisture Sensor. A strong correlation between terrestrial and remote sensing data was observed for 7 out of 11 selected indexes and the determination coefficient R2 values ranged from 67%– 87%. The best results were obtained for the NINSON index, with determination coefficient values of 87%, NSMI index (83.5%) and NINSOL (81.7%). We conclude that both hyperspectral and multispectral remote sensing data of bare soil moisture are valuable, providing good temporal and spatial resolution of soil moisture distribution in local areas, which is important for monitoring and forecasting local changes in climate.

Effect of biochar and biochar particle size on plant-available water of sand, silt loam, and clay soil

Biochar is being used as a soil amendment to improve soil hydraulic properties. It has been reported that biochar increases plant-available water, particularly in coarse-textured soils; however, effects on fine-textured soils are less pronounced. Here, we quantified the effects of biochar particle size on plant-available water in sand, silt loam, and clay soils. We amended these soils with a hydrophilic biochar, and packed soil-biochar mixtures into columns of 5.35-cm diameter and 3.0-cm height. Biochar was produced by gasification of woody forest residues. We applied the biochar at two different rates (0.5% and 2% by weight of C) and with four different biochar particle-size fractions (<4.75, <2.0, <1.0 and <0.5 mm). Our results show that biochar amendments increased the plant-available water (when expressed gravimetrically) of all three soils, particularly at the highest biochar application rate. Although the absolute increase in plant-available water was largest for the silt loam soil, the relative increase of plant-available water was greater for the sand than for the silt loam and clay. When expressed in volumetric terms, however, the effects on water retention were less pronounced: the sand showed a small increase in plant-available water with biochar amendment, and no change was observed with the silt loam and clay. Particle size of biochar had little effect on plant-available water (when expressed in gravimetric terms) in the three soils, but silt loam and clay showed increased plant-available water (when expressed in volumetric terms) with decreasing biochar particle size, while no effect was observed for the sand. While our findings corroborate many of the previously reported effects of biochar on soil-water retention, we show that the effects and their magnitude depend on whether the results are reported in terms of gravimetric or volumetric water contents. Because bulk density tends to decrease with increasing biochar application, so will the volumetric water content, and thus the magnitude of the effect on plant-available water will be smaller when expressed in volumetric water content.

Impacts of soil carbon on hydrological responses – a sensitivity study of scenarios across diverse climatic zones in South Africa

Soil organic carbon (SOC) content and the water holding capacity of soils are two properties which link the carbon and hydrological cycles. Hydrological model inputs seldom include soil carbon as a parameter even though soil carbon content is known to influence soil water retention capacities. This study is a sensitivity analysis of changes in hydrological responses when the model inputs include different soil carbon percentages for the topsoil horizon. Sensitivities of hydrological responses such as transpiration, runoff volumes, the stormflow component of runoff and extreme runoff events to SOC content were quantified under various climatic conditions in South Africa. The soil water holding capacities at the drained upper limit (i.e. field capacity), permanent wilting point and saturation were calculated for the topsoil horizon, using SOC dependent pedo (soil)-transfer functions for different soil carbon scenarios and locations in South Africa. These variables, together with other pre-determined soil- and locationrelated inputs, as well as 50 years of daily climate, were then used as inputs in a process-based hydrological model. Overall, it was found that increased SOC content in the topsoil horizon leads to an increase in transpiration, a reduction in runoff, especially in its stormflow component, and a reduction of extreme runoff events. However, these changes are relatively small compared to the influence of climate, particularly of rainfall amount and distribution.Significance:&#x0D; &#x0D; Organic carbon content of the soil and the water holding capacity of soils link the carbon and hydrological cycles.&#x0D; Management interventions that increase SOC lead to win-win situations because, in addition to climate change mitigation, plant water availability improves, and overall surface runoff ‘flashiness’ becomes more regulated.&#x0D; While rainfall amount and distribution over space and time remain the most critical determinants of hydrological responses, increased SOC in the topsoil horizon leads to increases in transpiration and thus plant growth, and to a reduction in runoff, especially in its stormflow component, and hence to a small reduction of severe flooding events.&#x0D;

Technical note: Accounting for snow in the estimation of root zone water storage capacity from precipitation and evapotranspiration fluxes

Abstract. A common parameter in hydrological modeling frameworks is root zone water storage capacity (SR[L]), which mediates plant water availability during dry periods as well as the partitioning of rainfall between runoff and evapotranspiration. Recently, a simple flux-tracking-based approach was introduced to estimate the value of SR (Wang-Erlandsson et al., 2016). Here, we build upon this original method, which we argue may overestimate SR in snow-dominated catchments due to snow melt and evaporation processes. We propose a simple extension to the method presented by Wang-Erlandsson et al. (2016) and show that the approach provides a lower estimate of SR in snow-dominated watersheds. This SR dataset is available at a 1 km resolution for the continental USA, along with the full analysis code, on the Google Colab and Earth Engine platforms. We highlight differences between the original and new methods across the rain–snow transition in the Southern Sierra Nevada, California, USA. As climate warms and precipitation increasingly arrives as rain instead of snow, the subsurface may be an increasingly important reservoir for storing plant-available water between wet and dry seasons; therefore, improved estimates of SR will better clarify the future role of the subsurface as a storage reservoir that can sustain forests during seasonal dry periods and episodic drought.

The spatiality of the soybean crop water deficit in Jales and Andradina microregions, state of São Paulo

Knowledge about soil water availability for future planning is the basis for carrying out its rational use. This work aimed to study the spatiality of water precipitation, crop evapotranspiration, and the need for water supplementation in soybean cultivation in the microregions of Jales-SP and Andradina-SP for the summer harvest. The water balance was determined by the Thorthwaite and Mather (1955) method, with data made available by the Agrometeorological Stations Network operated by the Hydraulics and Irrigation area of UNESP Ilha Solteira. We considered an available water capacity (AWC) of 40 mm. The study took place from the simulation of the water condition of a soybean crop sown on November 4, 2020. In the water deficit condition, the actual evapotranspiration (ETa) was considered null at a 20 % deficit, and the other values followed the same mathematical proportion. The mean rainfall of the period, crop evapotranspiration, and water deficit of each weather station were interpolated through ordinary circular kriging in ArcGIS 10.7 software. The water deficit in the soybean crop in the northwest region of São Paulo is related to the poor distribution of precipitation during the cycle and the significant recurrence of Indian summers all through the area. For the producers’ safety, investment in irrigation systems anticipating this poor distribution is justified. The water deficit in the region is variable. In years with good rainfall distribution, it can reach zero values, and in years with poor distribution, it can reach values greater than 180 mm.

Plasticity in response to plant-plant interactions and water availability.

The plastic responses of plants to abiotic and biotic environmental factors have generally been addressed separately; thus we have a poor understanding of how these factors interact. For example, little is known about the effects of plant-plant interactions on the plasticity of plants in response to water availability. Furthermore, few studies have compared the effects of intra- and interspecific interactions on plastic responses to abiotic factors. To explore the effects of intraspecific and interspecific plant-plant interactions on plant responses to water availability, we grew Leucanthemum vulgare and Potentilla recta with a conspecific or the other species, and grew pairs of each species as controls in pots with the roots, but not shoots, physically separated. We subjected these competitive arrangements to mesic and dry conditions, and then measured shoot mass, root mass, total mass and root : shoot ratio and calculated plasticity in these traits. The total biomass of both species was highly suppressed by both intra- and interspecific interactions in mesic soil conditions. However, in drier soil, intraspecific interactions for both species and the effect of P.recta on L.vulgare were facilitative. For plasticity in response to water supply, when adjusted for total biomass, drought increased shoot mass, and decreased root mass and root : shoot ratios for both species in intraspecific interactions. When grown alone, there were no plastic responses in any trait except total mass, for either species. Our results suggested that plants interacting with other plants often show improved tolerance for drought than those grown alone, perhaps because of neighbor-induced shifts in plasticity in biomass allocation. Facilitative effects might also be promoted by plasticity to drought in root : shoot ratios.

Effect of Re-Used Lignite and Mineral Wool Growing Mats on Plant Growth, Yield and Fruit Quality of Cucumber and Physical Parameters of Substrates in Hydroponic Cultivation

In hydroponic cultivation of vegetables with a solid substrate, mineral wool predominates. The pro-ecological policy and consumers’ expectations cause an increase in interest in organic substrates, which, when properly used, are less harmful to the environment. The aim of this study was to determine the effect of reusing lignite substrate in hydroponic cultivation on the growth, yield and quality of cucumber fruit and on the physical parameters of the substrate. The greenhouse cucumber cultivar ‘Mewa F1’ with semi-long fruits and smooth skin was used for the study. The plants were grown in the ‘Carbomat’ lignite substrate and ‘Grotop Master’ rockwool in two cycles. In cycle 1, new growing mats were used, while in cycle 2 the same growing mats as in cycle 1 were used again. In the hydroponic cultivation carried out on mineral wool and in the lignite substrate, both in the new and the reused substrate, the cucumber obtained mostly similar plant growth parameters and fruit color. Cucumber grown on the new mineral wool had a higher number and weight of fruits, which were characterized by a higher content of β-carotene and lutein compared to fruits from plants grown in the new lignite substrate. On the other hand, the reused lignite substrate resulted in higher cucumber yields and fruits with higher firmness and higher carotenoid content compared to cucumber grown on reused mineral wool. At the same time, the content of dry matter and sugar extract in fruits obtained from plants growing in the new and reused lignite substrate was higher compared to fruits grown in mineral wool. Both new and reused lignite substrate were characterized by very low plant-available water content. In contrast; the air and water holding capacity of lignite after cultivation did not change as much as that of mineral wool.

Effect of Low Zeolite Doses on Plants and Soil Physicochemical Properties.

Thousands of tons of zeolitic materials are used yearly as soil conditioners and components of slow-release fertilizers. A positive influence of application of zeolites on plant growth has been frequently observed. Because zeolites have extremely large cation exchange capacity, surface area, porosity and water holding capacity, a paradigm has aroused that increasing plant growth is caused by a long-lasting improvement of soil physicochemical properties by zeolites. In the first year of our field experiment performed on a poor soil with zeolite rates from 1 to 8 t/ha and N fertilization, an increase in spring wheat yield was observed. Any effect on soil cation exchange capacity (CEC), surface area (S), pH-dependent surface charge (Qv), mesoporosity, water holding capacity and plant available water (PAW) was noted. This positive effect of zeolite on plants could be due to extra nutrients supplied by the mineral (primarily potassium—1 ton of the studied zeolite contained around 15 kg of exchangeable potassium). In the second year of the experiment (NPK treatment on previously zeolitized soil), the zeolite presence did not impact plant yield. No long-term effect of the zeolite on plants was observed in the third year after soil zeolitization, when, as in the first year, only N fertilization was applied. That there were no significant changes in the above-mentioned physicochemical properties of the field soil after the addition of zeolite was most likely due to high dilution of the mineral in the soil (8 t/ha zeolite is only ~0.35% of the soil mass in the root zone). To determine how much zeolite is needed to improve soil physicochemical properties, much higher zeolite rates than those applied in the field were studied in the laboratory. The latter studies showed that CEC and S increased proportionally to the zeolite percentage in the soil. The Qv of the zeolite was lower than that of the soil, so a decrease in soil variable charge was observed due to zeolite addition. Surprisingly, a slight increase in PAW, even at the largest zeolite dose (from 9.5% for the control soil to 13% for a mixture of 40 g zeolite and 100 g soil), was observed. It resulted from small alterations of the soil macrostructure: although the input of small zeolite pores was seen in pore size distributions, the larger pores responsible for the storage of PAW were almost not affected by the zeolite addition.

Irrigation scheduling and requirements of processing tomato (Lycopersicon esculentum L.) in Eastern Canada

A 3-year study was conducted to determine the irrigation requirements for field tomato production in southwestern Ontario, Canada. Irrigation requirements were ascertained using both a weather-based crop water model, and data from soil moisture sensors. The equivalent irrigation depth applied based on real-time soil moisture measurements among four soil moisture treatments ranged from 102 to 168 mm, 85 to 190 mm, and 58 to 196 mm for 2008, 2009, and 2010, respectively. Using the crop simulation model—AquaCrop, the net irrigation water requirement (NIWR) was estimated as 163–236 mm over the 3-year period. The model overestimated the NIWR compared to the real-time sensor-based measurements. A comparison between these two approaches indicated that a soil moisture depletion of ≤ 45% available water content (AWC) resulted in adequate moisture to meet crop water requirements, and correspondingly produce higher crop yields. From this study, we conclude that real-time soil moisture sensors proved to be very effective for scheduling irrigation of processing tomatoes in Eastern Canada and leads to higher water savings.

Promotion of Growth and Physiological Characteristics in Water-Stressed Triticum aestivum in Relation to Foliar-Application of Salicylic Acid

The present work reports the assessment of the effectiveness of a foliar-spray of salicylic acid (SA) on growth attributes, biochemical characteristics, antioxidant activities and osmolytes accumulation in wheat grown under control (100% field capacity) and water stressed (60% field capacity) conditions. The total available water (TAW), calculated for a rooting depth of 1.65 m was 8.45 inches and readily available water (RAW), considering a depletion factor of 0.55, was 4.65 inches. The water contents corresponding to 100 and 60% field capacity were 5.70 and 1.66 inches, respectively. For this purpose, seeds of two wheat cultivars (Fsd-2008 and S-24) were grown in pots subjected to water stress. Water stress at 60% field capacity markedly reduced the growth attributes, photosynthetic pigments, total soluble proteins (TSP) and total phenolic contents (TPC) compared with control. However, cv. Fsd-2008 was recorded as strongly drought-tolerant and performed better compared to cv. S-24, which was moderately drought tolerant. However, water stress enhanced the contents of malondialdehyde (MDA), hydrogen peroxide (H2O2) and membrane electrolyte leakage (EL) and modulated the activities of antioxidant enzymes (superoxide dismutase (SOD), peroxidase (POD), and catalase (CAT), as well as accumulation of ascorbic acid (AsA), proline (Pro) and glycine betaine (GB) contents. Foliar-spray with salicylic acid (SA; 0, 3 mM and 6 mM) effectively mitigated the adverse effects of water stress on both cultivars. SA application at 6 mM enhanced the shoot and root length, as well as their fresh and dry weights, and improved photosynthetic pigments. SA foliage application further enhanced the activities of antioxidant enzymes (SOD, POD, and CAT) and nonenzymatic antioxidants such as ascorbic acid and phenolics contents. However, foliar-spray of SA reduced MDA, H2O2 and membrane permeability in both cultivars under stress conditions. The results of the present study suggest that foliar-spray of salicylic acid was effective in increasing the tolerance of wheat plants under drought stress in terms of growth attributes, antioxidant defense mechanisms, accumulation of osmolytes, and by reducing membrane lipid peroxidation.

Biochar application rate does not improve plant water availability in soybean under drought stress

Biochar, a form of porous pyrogenic carbon, has been shown to influence soil physicochemical properties and increase crop yield. However, it is unclear whether biochar application at different rates will improve crop performance in a clay soil under drought conditions through increasing plant water uptake. Here, we examined performance of soybean after amendment with biochar (pyrolysed at ~400 °C for 5 h) at four application rates (0, 25, 50 and 100 t ha−1) and grown under three moisture regimes (40%, 60% and 80% of field capacity). The instantaneous plant water content was determined periodically by recording relative water content, water retention capacity, and water uptake capacity in leaves while the cumulative water stress and water use efficiency (WUE) were determined from aboveground δ13C signatures and amount of water applied, respectively. The yield and yield attributes were also recorded. Results showed that across all drought treatments, biochar application significantly enhanced crop growth rate and increased total biomass production with a doubling in yield in the 100 t ha−1 biochar application. However, the seed yield did not increase with biochar application. Although biochar application improved WUE (biomass produced per unit of water applied), it most likely did not improve plant water uptake, since none of the measured plant water status indicators were affected by biochar. Instead, the enhanced biomass production may have been caused by an improvement in plant nutrition. Possibly, biochar application increased N acquisition through biological nitrogen fixation as there was a significant relationship between nitrogen (N) concentration in aboveground biomass and total biomass production. Moreover, application of biochar increased soil available potassium (K), and enhanced K uptake may have increased stress tolerance in soybean. Therefore, our findings show that biochar could improve plant performance in a clay soil by improving nutrient supply rather than by increasing water uptake.

Effect of different types of soil tillage for sunflower on some soil physical characteristics. Part I: soil moisture

Abstract The investigation was carried out during 2014–2016 in the land of General Toshevo town in the South Dobrudzha region on slightly leached chernozem soil type. The effect of the types of soil tillage for sunflower given bellow was followed: ploughing at 24–26 cm, chisel-plough at 24–26 cm, disking with disk harrow at 10–12 cm and direct sowing (no-tillage) on the soil moisture content. Based on bulk density, wilting point and the determined soil moisture content the plant-available water was calculated. The additional soil tilths of the areas subjected to ploughing, chisel-ploughing and disking with disc harrow included double spring pre-sowing cultivation with harrowing. To destroy the emerging weeds in the variant with direct sowing, a total herbicide was applied. The soil moisture content was evaluated during three main stages of sunflower development: emergence, flowering and technical maturity. The investigated parameter was determined for each of the studied layers – 0–10, 10–20, 20–30, 30–40 and 40–60 cm. In years with normal amounts of rainfalls, no significant differences in the soil moisture under the different ways of soil tillage were observed. Conventional ploughing and tillage without turning of the soil layer contributed to accumulation of more moisture and to higher moisture storage down the soil profile under heavy and intensive rainfalls. Tillage without turning of the soil layer, minimal and no tillage maintained more and better soil moisture in years with limited precipitation and in periods of drought.

Variable 21st Century Climate Change Response for Rivers in High Mountain Asia at Seasonal to Decadal Time Scales

AbstractThe hydrological response to climate change in mountainous basins manifests itself at varying spatial and temporal scales, ranging from catchment to large river basin scale and from sub‐daily to decade and century scale. To robustly assess the 21st century climate change impact for hydrology in entire High Mountain Asia (HMA) at a wide range of scales, we use a high resolution cryospheric‐hydrological model covering 15 upstream HMA basins to quantify the compound effects of future changes in precipitation and temperature based on the range of climate change projections in the Coupled Model Intercomparison Project Phase 6 climate model ensemble. Our analysis reveals contrasting responses for HMA's rivers, dictated by their hydrological regimes. At the seasonal scale, the earlier onset of melting causes a shift in the magnitude and peak of water availability, to earlier in the year. At the decade to century scale, after an initial increase, the glacier melt declines by the mid or end of the century except for the Tarim river basin, where it continues to increase. Despite a large variability in hydrological regimes across HMA's rivers, our results indicate relatively consistent climate change responses across HMA in terms of total water availability at decadal time scales. Although total water availability increases for the headwaters, changes in seasonality and magnitude may diverge widely between basins and need to be addressed while adapting to future changes in a region where food security, energy security as well as biodiversity, and the livelihoods of many depend on water from HMA.