Soil Water Tension Research Articles

Using stem water potential derived from continuous reading sensors for irrigation scheduling: nectarine as a test case

AbstractWe investigated on-site soil and plant based sensors translated to stem water potential for nectarine orchard irrigation control on heavy clay soil. Irrigation targeted predetermined stem water potential (SWP) thresholds for each phenological stage. Sensors were compared to SWP in six trees in a drying and wetting plot where irrigation was withheld periodically, allowing SWP to reach moderate water stress. Other sensor readings were regressed on SWP for those times, and the regressions were used for irrigation scheduling. The latter kept stage I and III SWP at ~ − 0.9 MPa, and moderate water stress in stage II (SWP ~ − 1.5 MPa). Weekly adjustments were made according to the thresholds. Results showed that tensiometers could be used for stages I and III, as they were very sensitive. However, when stress was applied soil water tension exceeded tensiometer range at 30 cm depth.Soil water content sensors had slower responses than the others, so they might be difficult to use for precise irrigation in heavy soils. Dendrometers responded quickly and therefore might be more useful for management even in moderate water stress, even with their sensitivity to climatic conditions. Analysis showed to maintain SWP within ± 0.1 MPa, 2 tensiometers, 10 soil water content sensors and 7 dendrometers stations are needed. Signal-to-noise (SNR) ranks were SWP > 30 cm tensiometers > 60 cm tensiometers > dendrometers > 30 cm soil water content > 60 cm soil water content sensors for the full season. Nonetheless, in some stages tensiometer SNR was greater than that of SWP.

Water Requirements, Soil Moisture Availability, and Their Effects on Quinoa (Chenopodium quinoa Willd.) Development and Yield

Throughout the world, about 70% of the total water is used for irrigation. Reports show that there will be a significant increase in irrigation requirements, as irrigation is an important factor affecting water footprint and productivity worldwide [45]. The experiment described in this article was carried out at the Agricultural Research Station, Ministry of Agriculture, Iraq, in 10 kg pots to evaluate the effects of soil moisture availability on water requirements, water productivity, and quinoa crop productivity under different irrigation treatments. These treatments maintained the soil at different levels of soil water tension (-0.05, -0.10, -0.15, -0.30, and -0.40 MPa) during the vegetative and/or reproductive periods of growth. The study analyzed water consumption, plant growth, yield components, and water productivity of the quinoa crop. The data showed that evapotranspiration decreased with increasing soil moisture tension during both the vegetative and reproductive periods of development. The maximum water productivity was consistently recorded at the lowest soil moisture tension, highlighting moisture efficiency. It was concluded that quinoa is relatively tolerant to soil moisture stress during the vegetative period compared to the reproductive period. The number of grains per ear was identified as a limiting factor for grain yield.

Modeling the response of crop emergence to sowing depth and soil water deficit in direct-seeded rice

Abstract Background and aims Dry direct seeding of rice in the tropics often suffers from poor crop establishment owing to soil water deficit. A potential solution is sowing deeply to utilize residual soil moisture farther below the surface. We evaluated rice emergence under various sowing depths and soil moisture conditions and tested a model framework of it as a simultaneous function of sowing depth and soil moisture. Methods We combined data from three field experiments and one growth chamber experiment to collect emergence data for four rice cultivars (Dontokoi, Dular, Rc222 and Rc420). We independently parameterized the relationships between emergence and sowing depth or soil water tension using logistic functions. We expressed the final emergence as the product of the two functions. Results Emergence responses to sowing depth and soil moisture fitted the cultivar-specific logistic functions well. For Dular, a cultivar that tolerates deep sowing, emergence was greatest when sown at 4 to 5 cm below the surface under soil water deficit, versus 1 to 2 cm under wet conditions, and our combined model successfully reproduced this result. Conclusion Our emergence model framework supports adjustment of sowing depth to account for available soil water, making the model a powerful new tool for drought adaptation in direct-seeded rice.

Hydrological and pedological effects of combining Italian alder and blackberries in an agroforestry windbreak system in South Africa

Abstract. The Western Cape in South Africa is a water-scarce region which will likely receive less rainfall and higher air temperatures under projected climate change scenarios. The integration of trees within agricultural systems provides an effective measure for improving water retention on agricultural land. Studying an established and irrigated agroforestry system (AFS) combining alder (Alnus cordata (Loisel.) Duby) as a linear windbreak with a blackberry (Rubus fructicosus L.) crop, we explore the water use dynamics of the intercrop as influenced by the windbreak element by combining methods from hydrology, soil science and forestry disciplines. Our objective is to explore whether the AFS positively impacts the water balance by combining measurement campaigns to characterise the spatial variability of various key system properties with continuous monitoring. The campaigns encompassed extensive soil sampling to determine soil characteristics (nutrient concentrations, hydraulic conductivity, texture, water retention) in the laboratory as well as terrestrial laser scans of the field site, especially of the windbreaks. The continuous measurements covered meteorological, soil water content and soil water potential observations over a 6-month period (in summer). These were applied to understand soil water dynamics during rainstorms and dry spells, including root water uptake as well as soil water storage. We recorded a total of 13 rainfall events delivering 2.5–117.6 mm of rainfall with maximum intensities of 4.1 to 82.6 mm h−1. Further analyses showed that infiltration is likely dominated by preferential flow, with root water uptake potentially occurring in two depth zones corresponding to different plant communities. While soil water content varied by depth and was influenced by physical and environmental factors, it was generally higher in the intercrop zone than within the windbreak-influenced zone. During dry spells, soil water content did not drop below the water content of the permanent wilting point (<-1500 kPa). Values corresponding to soil water tensions above 1000 kPa were recorded on several occasions; these were mitigated by irrigation and, thus, did not result in water stress. Nutrient distribution and soil physical properties differed near the windbreak in comparison to the blackberry crop, and the carbon sequestration potential is great in comparison to monoculture farming. We could demonstrate positive effects of the windbreak on the water balance and dynamics in the blackberry field site, even though questions remain as to the extent of these benefits and how they compared to disadvantageous aspects brought about by the presence of the trees (e.g. increased water usage). Irrigation did, in fact, shift the AFS from a water-limited regime to an energy-limited one.

Steps toward an integrated soil water tension and osmotic tension sensor

Steps toward an integrated soil water tension and osmotic tension sensor

Measurements of Soil Water Potential and Conductivity based on a Simple Evaporation Experiment using a Hydraulic Property Analyzer.

The measurement of soil hydraulic properties is critical in understanding the physical components of soil health as well as integrated knowledge of soil systems under various management practices. Collecting reliable data is imperative for informing decisions that affect agriculture and the environment. The simple evaporation experiment described here uses instrumentation in a laboratory setting to analyze soil samples collected in the field. The soil water tension of the sample is measured by the instrument, and tension data is modeled by software to return soil hydraulic properties. This method can be utilized to measure soil water retention and hydraulic conductivity and give insight into differences in treatments or environmental dynamics over time. Initial establishment requires a user, but data acquisition is automated with the instrument. Soil hydraulic properties are not easily measured with traditional experiments, and this protocol offers a simple and optimal alternative. Interpretation of results and options for extending the data range are discussed.

Drought-Stressed Apple Tree Grafted onto Different Rootstocks in a Coastal Sandy Soil: Link between Fast Chlorophyll a Fluorescence and Production Yield

Domesticated apple is a drought-sensitive species that spread from continental to Mediterranean temperate regions, where it can particularly experience prolonged water stress. One strategy to improve drought resistance in apple is engrafting on selected rootstocks. This study explores the potential of fast chlorophyll a fluorescence for the comparison of rootstock sensitivity to drought, looking for significant correlations with fruit productivity. The experiment was conducted in a field located in the coastal Po River Plain, Northern Italy, characterized by a loamy sandy soil, particularly prone to drought (86% sand). Mature plants of apple cv. Superchief® Sandidge engrafted on three different rootstocks (CIVP21pbr, MM106, M26) were monitored throughout the summer of 2021 and compared between irrigated and non-irrigated parcels, and at the end of the season, fruit production was evaluated. Despite soil water tension only reaching −13 kPa, the non-irrigated plants experienced a small but consistent loss of Photosystem II (PSII) activity and a lesser capacity of light energy conservation in the photosynthetic electron transport chain. The fruit weight correlated with PSII photochemical indexes recorded during early drought, particularly FV/FM and PIABS; a correlation emerged between fruit number per plant and median values of electron transport parameters, including PITOT. Although all rootstocks underwent a 40% loss of productivity, the fluorescence parameters revealed a graded susceptibility to drought, M26 > CIVP21pbr > MM106, which matched well with the plant vigour. The least drought-sensitive MM106 produced less numerous but heavier fruits than the other two rootstocks.

Evaluation of Soil Water Tension Trigger Levels for Optimizing Peanut (Arachis hypogaea) Yield and Irrigation Water Use Efficiency

Irrigation technologies have provided the ability for growers to effectively manage crops. In recent years, soil moisture sensors have provided more precise soil moisture readings for continued improvement of irrigation decisions. Trigger level irrigation research was first performed on corn (Zea mays L.) and cotton (Gossypium hirsutum L.), but southeastern crop growers often include peanut (Arachis hypogaea L.) in crop rotations. Therefore, research was performed on peanut to determine how differing soil water tension (SWT) trigger levels affected peanut yield. Soil water tension sensors connected to a real-time data logger were used to test irrigation trigger levels in peanut plots during the 2018 and 2019 growing seasons at the University of Georgia (UGA) Stripling Irrigation Research Park (SIRP) in Camilla, Georgia. Nine different treatments were implemented, which included 20, 30, 40, 50, 60 kPa SWT, USDA-ARS Irrigator Pro, UGA Checkbook, 50% UGA Checkbook, and rainfed. Twenty-seven plots were established in a randomized complete block design with three replications. At the conclusion of this study, it was determined that there were no differences on yield within year, but year had an effect on peanut yield (P < 0.05), and treatment within year had a significant effect on irrigation water use efficiency (IWUE) (P < 0.05).

The Influence of Sprinkler and Drip Irrigation on the Incidence and Severity of Bacterial Disease in Onions Grown in Northeast California

Overhead sprinkler irrigation and its effect on leaf wetness are often referenced as a key factor for bacterial disease spread in onions grown in arid climates. A study was conducted in 2021 and 2022 in Tulelake, California, to compare the incidence and severity of bacterial disease under sprinkler and drip irrigation. The experiment was a split-plot randomized complete block design with drip and solid-set sprinkler irrigation as the main plot treatments and inoculation and no inoculation with plant-pathogenic bacteria as the split-plot treatments. The entire study area was irrigated with solid-set sprinklers from planting until the five-leaf stage to facilitate uniform onion germination and chemigation of herbicides for weed control. After the five-leaf stage, irrigation treatments were imposed for the remainder of the growing season. Total irrigation water amount and irrigation frequency were similar for both irrigation methods. Foliar disease severity and the incidence of bulb rot were 170 and 186% higher, respectively, for solid-set sprinkler compared with drip irrigation. Leaf wetness within the plant canopy during onion bulbing was on average 36% higher in the solid-set sprinkler compared with drip irrigation treatment, whereas relative humidity and temperature were similar between irrigation methods. Drip irrigation maintained lower soil water tension and increased average bulb size by 9% compared with solid-set sprinkler irrigation. This study confirms historical observations that overhead irrigation can extend leaf wetness and increase bacterial disease in onions in arid production areas and highlights the potential benefits of the adoption of drip irrigation.

Mitigating soil water deficit using organic waste compost and commercial water retainer: a comparative study under semiarid conditions

Semiarid regions have particularly been confronted with climate change effects reflected by the consistent decrease of rainfall and increase of evapotranspiration. This drought stress constitutes the main constraint for agricultural production improvement, which is aggravated by the fact that strategic (field) crops are mostly grown under rainfed systems. Therefore, the objective of this field study was to improve soil water retention by the application of two conditioners namely, an organic waste compost (DS) and a synthetic water-retaining hydrogel (WS). These amendments were applied to an agricultural soil for the cultivation of fodder maize under normal and deficit irrigation regimes. Advanced analysis showed a general disruption of plant growth parameters under water stress. However, both amendments attenuated this negative effect with respect to control by improving soil water status. More precisely, the measured soil water tension at the start of the dry season was the lowest in presence of DS (48 centibars), followed by WS (61 centibars), then unamended soil (83 centibars). Besides, compost application resulted in higher moisture (13.3%), nitrogen (0.36%), and organic matter (0.56%) in soil than the synthetic hydrogel at the end of the field experiment. Soil and plant characterization highlighted the combined effect of water deficit and conditioner type. Indeed, the consistent increase of soil water content in the presence of DS and WS improved all the addressed plant parameters when compared with untreated soil. Infrared thermal imaging showed that canopy temperature was lower in presence of both amendments while dry biomass yield increased by 38% when water supply was limited. Nevertheless, the long-term sustainability of the soil system appears to be better maintained in the presence of the organic waste compost. The latter has the added advantage of improving soil fertility in contrast to inert polymers.

Suitability of the stress severity index combined with remote‐sensing data as a tool to evaluate drought resistance traits in potato

AbstractPotato is a drought susceptible crop and even short drought spells reduce tuber yields notably. In an earlier study we developed a stress severity index (SSI) based on the development stage of a genotype at the onset of drought and the soil water deficit based on soil water tension. Here, we test the suitability of the SSI combined with remotely sensed data as a screening tool to select drought‐tolerant potato genotypes. Normalized difference vegetation index (NDVI) and the photochemical reflectance index (PRI) were obtained from reflectance measurements and thermography. Temperature data from the thermography allow using the difference between leaf and air temperature (∆T) to estimate the transpirational cooling of the leaves. Via cluster analysis including SSI, tuber yield reduction under drought, NDVI, PRI and thermography, three groups were distinguished: 1. SSI < 1000 with fast decreasing NDVI, PRI and ∆T, 2. SSI 1000–2000 with almost constant NDVI and ∆T and 3. SSI > 2000 described by small changes of NDVI, PRI and temperature deficit. For SSI < 1000, ∆T, PRI and NDVI showed to be good indicators of genotypic performance under drought. Potential strategies for drought resistance in potato detectable through remote sensing are discussed.

Effect of water management on human exposure to inorganic arsenic and other trace elements through rice consumption

Arsenic (As) is widely spread in the environment. Its inorganic form (i-As) is carcinogenic. Rice is a global staple food and an important source of calories, nutrients, As and other elements. The use of aerobic conditions or intermittent ponding during cultivation is one of the strategies to decrease As contamination in rice grains. The present study investigated whether different soil water tensions (SWTs) applied at different phenological phases (Ph.Ph.) may affect the accumulation and human exposure to essential and potentially toxic elements (PTEs) including As species. The results showed that rice husks accumulate a major fraction of some elements, including 80-96% of the Pb. It was observed that the higher SWT in the Ph.Ph. R1 was responsible for a 45% decrease in As in whole grains and an increase of more than 3000% in Cd, compared with the flooded treatment in the vegetative period. Higher SWT in Ph.Ph. R1 and R2 decreased the risk associated with As daily intake. Health risk assessments revealed potential non-carcinogenic risks associated with the combined effect of exposure to PTE, as well as carcinogenic risks related to As. Water management is a useful strategy to mitigate these risks from rice intake.

Measurement of Water Matriial Potential in the Soil Through Instrumented Tensiometers with Pressure Sensors and Puncture Device

Objective: The search for a practical and accessible solution for measuring water tension in the soil using tensiometers is fundamental for irrigation management, efficient use of water and increased profitability of irrigated crops. The objective of this study was to propose a technique based on the instrumentation of a tensiometer with a pressure sensor and a device for reading the sensor's response. Theoretical Frame: This study used the following main quotes as a theoretical basis: Freescale and NPX Semiconductors manufacturers of pressure sensors, Azevedo & Silva for the soil water tension correction methodology and Van Genuchten to describe the relationship between soil water content and suction. Method: Pressure transducers with a range of 0-50 and 0-100 kPa were used, with an analog signal varying between 200 and 4700 mV, whose response was measured by a digital multimeter with the scale adjusted to V or mV. The transducer was adapted by attaching a hypodermic needle Nº 7/30 to the vacuum measurement inlet, leaving the other inlet free for the atmosphere. The transducer was powered by a 9 Vcc battery with rectified voltage to 5 Vcc through a specific integrated circuit for this function. The conversion of the transducer response signal in mV to voltage in kPa was performed using the response function informed by the manufacturer, reversing the order of the variables so that the voltage could be measured as a function of the output signal in mV. The system was used to measure the water tension in the soil of tensiometers installed in an area cultivated with tomatoes in a greenhouse during a complete cycle, functioning satisfactorily. Results and conclusions: During the experimental period, the water tension in the soil observed with the new tensiometer with pressure sensor and sensor response reading device ranged from 0.00 kPa (minimum tension) to 53.33 kPa (maximum tension) in the two soil layers. analyzed soil, while the average tension was 23.64 kPa in the 0-20 cm soil layer and 21.38 kPa in the 20-40 cm layer. Soil moisture obtained from soil water tension and soil water retention curve ranged from 0.11 (minimum) to 0.50 m3 m-3 (maximum) in both studied soil layers, while that the average soil moisture in the depth from 0 to 20 cm was 0.21 m3 m-3 and from 20 to 40 cm was 0.20 m3 m-3. The instrumented tensiometer with pressure sensor and sensor response reading device makes it possible to satisfactorily determine the matrix potential of water in the soil. The matriial tension data obtained with the new pressure sensor are consistent with reports in the literature as adequate to provide higher yields in tomato cultivation. The technique and instrumentation proposed in this study allows measuring the water tension in the soil, knowing the soil moisture and carrying out irrigation management, applying an irrigation depth according to the needs of the plants, making a more efficient use of water and providing water and electricity savings. Implications of the research: This study qualifies as being of great relevance for the purposes of the Department of Agronomic Engineering at the Universidade do Estado de Mato Grosso, Nova Mutum Campus, as well as for the entire academic and scientific community and rural producers interested in tensiometers to carry out a management of water from the soil and farm sustainably. Originality and value: The study sought to present to the academic, scientific and rural producers community a practical and accessible solution for measuring the water tension in the soil through tensiometers, thus providing current information on a new instrument for irrigation management, which makes it possible to carry out a more efficient use of water and increase the profitability of irrigated crops.

Crescimento e produção de cultivares de trigo sob tensões de água em solo de Cerrado

ABSTRACT Brazil is not self-sufficient for the production of wheat (Triticum aestivum L.), and the expansion of cultivation to the Cerrado in the State of Mato Grosso, in an irrigated system, is an alternative solution to increase wheat production. This study aimed to evaluate the effects of soil water tension on the growth and production of wheat cultivars cultivated in the Cerrado Oxisol. The treatments were arranged in a 3 × 5 factorial scheme, with three wheat cultivars (BRS 254, BRS 394, and BRS 264) and five water tensions in soil (5, 15, 25, 35, and 45 kPa), using a randomized block design with four replications. Wheat growth and production exhibited a better response at a tension of 5 kPa. Cultivar BRS 254 showed the lowest production of spikes and grains per spike with increasing soil water tension. Among the cultivars, BRS 264 produced the highest number of grains per spike at tensions of 35 and 45 kPa. The wheat cultivars BRS 254, BRS 394, and BRS 264 have high water requirements. However, BRS 264 presented greater growth and production under conditions of restricted water in the soil, being able to be cultivated with an irrigation system activated less frequently, with less expenditure of water and energy.

Ice wedge polygon stability on steep slopes in West Greenland related to temperature and moisture dynamics of the active layer

AbstractIce wedge polygons on steep slopes have generally been described as being covered by periglacial sediments and, typically, the active layer on slopes becomes mobile during thaw periods, which can lead to solifluction. In West Greenland close to the ice margin, however, the active layer and ice wedge polygons are stable despite their occurrence on steep slopes with inclinations of ≥30°. We conducted a soil survey (including sampling for soil analyses and radiocarbon dating) in the Umimmalissuaq valley and installed a field station ~4 km east of the current ice margin to monitor soil temperature and water tension at depths of 10, 20 and 35 cm of the active layer on a steep, north‐facing slope in the middle of an ice wedge polygon from 2009 to 2015. Thawing and freezing periods lasted between 2 and 3 months and the active layer was usually completely frozen from November to April. We observed simultaneous and complete water saturation at all three depths of the active layer in one summer for 1 day. The amount of water in the active layer apparently was not enough to trigger solifluction during the summer thaw, even at slope inclinations above 30°. In addition, the dense shrub tundra absorbs most of the water during periods between thawing and freezing, which further stabilizes the slope. This process, together with the dry and continental climate caused by katabatic winds combined with no or limited frost heave, plays a crucial role in determining the stability of these slopes and can explain the presence of large‐scale stable ice wedge polygon networks in organic matter‐rich permafrost, which is about 5,000 years old. This study underlines the importance of soil hydrodynamics and local climate regime for landscape stability and differing intensities of solifluction processes in areas with strong geomorphological gradients and rising air temperatures.

Influence of Water Stress on Canopy Temperature and Yield Contributing Characteristics of Wet Seeded Rice

Canopy temperature (CT) is one of the indices for evaluating water stress. The study has been taken to correlate water stress with CT and to evaluate effect of water stress on crop and yield performance of wet seeded rice (WSR). The canopy temperature of rice at vegetative and flowering stages were investigated under different soil water stresses. The field experiment was conducted at IRRI (International Rice Research Institute) during dry season, 2011. Three levels of water stress (-10, -20 and -40 kPa) were applied at 3-leaf (3L) to panicle initiation (PI), PI to flowering (FL) and FL to physiological maturity (PM) stages. One non -stressed treatment, i.e., continuously flooded puddled transplanted rice (PTR-CF) was used as a control. Soil water tension was measured using a 30-cm long gauge tensiometer and a handheld infrared thermometer was used to measure CT. Canopy temperatures were recorded from 3L to PI and PI to FL stages. In both the stages, CT was within the range of marginal stress. Canopy temperature depression (CTD) was higher in the stressed condition than that of the nonstressed. At the PI stage, leaf area index (LAI) was significantly lower in WSR than PTR -CF. LAI was comparatively lower in WSR with -20 kPa and -40 kPa than WSR with -10 kPa and PTR-CF when water stress imposed during PI-FL. Decreasing grain yield was observed when irrigation threshold increased from -10 to -40 kPa during PI to FL and FL to PM, but the differences were not significant. Yield components of WSR with different stresses were not significantly different. But spikelet fertility (%) and grain weight (g) of WSR was significantly higher than that of PTR-CF. The yield of PTR-CF was similar to the yield of WSR. Panicle/m2 correlated negatively with CT under a stressed condition. Yield and all yield components ex cept spikelet per panicle were positively correlated with CT at 60 days after seeding (CT 60). Under stressed condition, CT correlated negatively with the grain yield. Results revealed that CT correlated positively with grain yield under non-stressed condition (CT35 and CT60). Spikelet fertility percentage (SF%) correlated negatively with CT35 and CT46. It has been concluded that CT and CTD may be used for water stress evaluation. Bangladesh Rice J. 25 (2) : 69-76, 2021

Impact of sensor placement in soil water estimation: a real-case study

One important problem in implementing a closed-loop irrigation system is the determination of the optimal locations to install the sensors, both vertically and horizontally, such that improved pressure head estimation can be obtained. In this work, we find the best locations of the sensors in terms of degree of observability in an actual field and investigate whether the optimal sensor placement can significantly improve the pressure head estimation performance in actual applications. We investigate the impact of sensor placement in pressure head estimation for an actual agricultural field in Lethbridge, Alberta, Canada. In an experiment on the studied field, 42 watermark sensors were installed at different depths to collect the soil water tension measurements. A three-dimensional agro-hydrological model with heterogeneous soil parameters of the studied field is set up. The modal degree of observability is applied to the three-dimensional system to determine the optimal sensor locations. The extended Kalman filter (EKF) is chosen as the data assimilation tool to estimate the pressure head of the studied field. Pressure head estimation results for different scenarios are obtained and analyzed to investigate the effects of sensor placement on the performance of pressure head estimation in the actual applications. Estimation results indicate that optimally placed sensors reduce the average root mean square error by about 30% compared to the case the sensor positions are selected randomly.

Modelling the potential for peat-block transplants to restore industrially contaminated Sphagnum peatlands

For centuries, humans have inadvertently been contaminating peatlands due to industrial emission of pollutants that degrade key peatland ecosystem functions, such as carbon sequestration. Returning the ecosystem functionality to these degraded peatlands remains a challenge due to adverse ecohydrological conditions and elevated peat pollutant concentrations, such as nickel (Ni) and copper (Cu), at the remnant peat surface. However, field-scale trials can be labour, time, and monetarily expensive with no guarantee of success. As a precursor to field-scale trials, we use a 10-year coupled hydrological and solute transport models in Hydrus-1D to assess the feasibility of using peat-block transplants to restore a peatland contaminated by Ni and Cu. The exceedance of critical capitula hydrological (soil water tension >100 mbar) and chemical ([Ni] and [Cu] > 10−6 mmol mL−1) thresholds that correspond with increased Sphagnum physiological stress were assessed using a series of modelled scenarios with varying peat-block thicknesses (5 to 30 cm in 5 cm increments), Sphagnum species (S. fuscum, S. rubellum, S. magellanicum, and an average Sphagnum), and initial contaminant loads (i.e., distance from a smelter). When the remnant peat contaminant load was largest (i.e., closer to a smelter) and the transplant thickness was 5 cm, the combined hydrological threshold and chemical thresholds in the capitula were exceeded in as little as least 2 years, while thicker transplants did not exceed the concentration threshold after 10 years. In general, the average Sphagnum exceeded the hydrological threshold most, followed by S. magellanicum, S. rubellum, and S. fuscum, respectively. A Monte Carlo and sensitivity analyses showed that the results of our modelling scenarios were generally robust. Based on these results, we suggest that targeting thicker (>20 cm) peat-blocks of S. fuscum and S. rubellum (i.e., densely growing Sphagnum spp.), would likely provide a suitable peat-block for transplant. This research provides a critical path forward for restoring contaminated and degraded peatlands.

Correlation of UAV and satellite-derived vegetation indices with cotton physiological parameters and their use as a tool for scheduling variable rate irrigation in cotton

Current irrigation management zones (IMZs) for variable rate irrigation (VRI) systems are static. They are delineated in the beginning of the season and used thereafter. However, recent research has shown that IMZ boundaries are transient and change with time during the growing season. The primary goal of this study was to explore the potential of using vegetation indices (VIs) developed from unmanned aerial vehicle (UAV) and satellite images to predict cotton physiological parameters that can be used to delineate in-season boundaries of IMZs. A 2 year study was conducted in a 38 ha commercial cotton field in southwestern Georgia, USA. Throughout the two growing seasons, VIs were calculated from UAV, PlanetScope, and Sentinel-2 images. Predawn leaf water potential (LWPPD) and plant height were measured at 37 locations in the field on the same day as the flights and correlated with UAV and satellite based-VIs. GNDVI (Green normalized difference vegetation index) was the best predictor of plant height with correlation values of 0.72 (p < .0001) and 0.84 (p < .0001) for 2019 and 2020, respectively. A secondary goal was to compare the performance of dynamic VRI (DVRI) to conventional irrigation. The field was divided into alternating parallel conventional, and DVRI strips to compare the two scheduling methods. The conventional strips were irrigated using the farmer’s standard method and individual IMZs within the DVRI strips were irrigated based on soil water tension (SWT) measured with a wireless soil moisture sensor network. LWP and SWT measurements correlated well. IMZs were initially delineated using soil texture, apparent soil electrical conductivity (ECa), and yield maps and satellite images from previous years and were modified in-season to reflect patterns observed in the plant height maps. In 2020, the DVRI system prescribed an average irrigation amount of 50.8 mm while conventional irrigation applied an average of 58.4 mm. Average yields for DVRI and conventional were 1248 and 1191 kg ha−1, respectively. The DVRI system resulted in average yield 4.6% higher than conventional irrigation, while applying 14.0% less water. Despite the lower water application by the DRVI system, the performance comparison between the DRVI and the conventional irrigation was not conclusive.

Economic viability and development of radish (Raphanus sativus L.) under different soil water tensions and mulching types

There is a lack of information on the production of irrigated radish associated with the use of mulching and on the economic viability of these production technologies. The objective of this study was to evaluate the growth, yield, and economic viability of the radish crop under different soil water tensions (SWT) and mulching types. The experiment was conducted in a greenhouse. During the experiment, the following variables were evaluates: growth parameters, yield and economic viability. SWT at 7 kpa in the treatments without mulching and at 12 kPa in the treatments with black plastic and black non-woven resulted in higher growth parameters and yield. The leaf area index and the root diameter were the parameters that had a high and positive correlation with yield. Expenses with variable resources represent on average 75% of the total production cost. Therefore, the investment pays all resources applied in the activity and provides an economic profit. In this context, the higher radish yield with 37.5 t ha-1 provided the highest profitability of the evaluated treatments, thus, for radish production, the recommendation is to use 12 kPa as an indicator of the moment for irrigation, associated with the use of black plastic.