Soil Water Probes Research Articles

Soil water depletion of peanut subspecies as influenced by water‐use traits and soil water availability

AbstractWhile improved crop water‐deficit tolerance is considered of primary importance, many phenotyping efforts focusing on quantifying structural root traits make assumptions about architecture representing root function. Therefore, the aim of this study was to quantify whole plant water‐use traits among disparate peanut (Arachis hypogaea L.) genotypes and determine their impact on water‐deficit tolerance. Mini‐rhizotrons were installed to evaluate genotypic root architecture and developmental changes to two irrigation regimes imposed during early development. Following the early‐season irrigation regimes, above‐ and below‐ground traits were studied across a range of soil water conditions through measures of: (a) leaf‐level gas exchange and (b) soil water depletion quantified using a novel soil water probe inserted into mini‐rhizotrons allowing for matched root architecture and soil water depletion measures. While differential water treatments influenced root system architecture development among the genotypes, soil water depletion locations were primarily determined by water availability in the soil profile, not simply by having greater root length at a given soil location. This contradicts the assumption that greater root presence is a consistent indicator of increased root activity. Phenotypic selection of root traits for improving the efficiency of crop water use should consider both structural and functional traits in relation to the intended production environments slated for future cultivar development.

Modeling Approaches for Determining Dripline Depth and Irrigation Frequency of Subsurface Drip Irrigated Rice on Different Soil Textures

Water saving techniques such as drip irrigation are important for rice (Oriza sativa L.) production in some areas. Subsurface drip irrigation (SDI) is a promising alternative for intensive cropping since surface drip irrigation (DI) requires a higher degree of labor to allow the use of machinery. However, the semi-aquatic nature of rice plants and their shallow root system could pose some limitations. A major design issue when using SDI is to select the dripline depth to create appropriate root wetting patterns as well as to reduce water losses by deep drainage and evaporation. Soil texture can greatly affect soil water dynamics and, consequently, optimal dripline depth and irrigation frequency needs. Since water balance components as deep percolation are difficult to estimate under field conditions, soil water models as HYDRUS-2D can be used for this purpose. In the present study, we performed a field experiment using SDI for rice production with Onice variety. Simulations using HYDRUS-2D software successfully validated soil water distribution and, therefore, were used to predict soil water contents, deep drainage, and plant water extraction for two different dripline depths, three soil textures, and three irrigation frequencies. Results of the simulations show that dripline depth of 0.15 m combined with one or two daily irrigation events maximized water extraction and reduced percolation. Moreover, simulations with HYDRUS-2D could be useful to determine the most appropriate location of soil water probes to efficiently manage the SDI in rice.

Modeling Soil Nitrate Accumulation and Leaching in Conventional and Conservation Agriculture Cropping Systems

Nitrate is a major groundwater inorganic contaminant that is mainly due to fertilizer leaching. Compost amendment can increase soils’ organic substances and thus promote denitrification in intensively cultivated soils. In this study, two agricultural plots located in the Padana plain (Ferrara, Italy) were monitored and modeled for a period of 2.7 years. One plot was initially amended with 30 t/ha of compost, not tilled, and amended with standard fertilization practices, while the other one was run with standard fertilization and tillage practices. Monitoring was performed continuously via soil water probes (matric potential) and discontinuously via auger core profiles (major nitrogen species) before and after each cropping season. A HYDRUS-1D numerical model was calibrated and validated versus observed matric potential and nitrate, ammonium, and bromide (used as tracers). Model performance was judged satisfactory and the results provided insights on water and nitrogen balances for the two different agricultural practices tested here. While water balance and retention time in the vadose zone were similar in the two plots, nitrate leaching was less pronounced in the plot amended with compost due to a higher denitrification rate. This study provides clear evidence that compost addition and no-tillage (conservation agriculture) can diminish nitrate leaching to groundwater, with respect to standard agricultural practices.

Simulation of Mulch and No-Mulch Conditions for Various Soil Matric Potential Thresholds for Drip-Fertigated Guava ( Psidium guajava L.) in the Semiarid Region of Northwest India

AbstractField experiments were conducted in a semiarid region of Punjab state, northwest India, for 2 years to evaluate an efficient irrigation schedule for guava under mulch and no-mulch conditions. The experiment involved the effect of mulching and three irrigation threshold values [I1 (−20 kPa); I2 (−40 kPa); and I3 (−60 kPa)] on guava plants under drip irrigation and fertigation. Soil matric potential, irrigation amount, soil water content, and fertilizer (N, P, and K) content were measured, and seasonal crop evapotranspiration as well as water and fertilizer use efficiency were computed regularly during the growing period of the crop. The calibrated two dimensional (2D)/three-dimensional (3D) model was used to simulate soil matric potential, and water and fertilizer movement in the soil under guava trees for mulch and no-mulch conditions. Simulated water movement, soil matric potential, and N, P, and K movement statistically matched those measured using the tensiometers, soil water probes, and soi...

Calibration and Application of Aquaflex TDT Soil Water Probes to Measure the Soil Water Dynamics of Agricultural Topsoil in Southwest Germany

Soil water plays a key role in crop growth and yield formation. A sustainable irrigation management depends on a reliable soil water monitoring. The present study was conducted to derive site-specific and pedotransfer calibrations for Aquaflex time domain transmission (TDT) soil water sensors and to test their performance under field conditions. In spring 2009, two soil moisture networks were installed in the Kraichgau region and in the Swabian Alb, southwest Germany. Each network consists of 21 stations, each equipped among others with an Aquaflex TDT sensor installed 15-cm-deep in the soil. At each station, soil samples were taken and analyzed for the gravimetric soil water content, bulk density, soil texture, electrical conductivity, pH, and organic nitrogen and carbon content. The factory calibration delivered highly biased soil water contents [∼−8.0 Volume (Vol.) %]. The root mean square errors (RMSEs) were high, reaching on average 8.3 and 12.6 Vol.% in Kraichgau and Swabian Alb, respectively. The RMSEs of pedotransfer calibrations declined to 3.7 Vol.% in Kraichgau and to 3.4 Vol.% in Swabian Alb. In both regions, the slope of the calibration curve was affected by soil bulk density. High-leverage independent variables affecting the intercept were electrical conductivity in Kraichgau and silt fraction in Swabian Alb. Site-specific calibrations performed best. On average, the RMSE in Kraichgau was 3.0 Vol.%, in Swabian Alb 1.9 Vol.%. The pedotransfer-based approach proposed in the present study is a good compromise between labour effort and accuracy for soil landscapes with similar texture and properties.

Evaluation of water movement and nitrate dynamics in a lysimeter planted with an orange tree

Adoption of high input irrigation management systems for South Australian horticultural crops seeks to provide greater control over timing of irrigation and fertilizer applications. The HYDRUS 2D/3D model was used to simulate water movement in the soil under an orange tree planted in a field lysimeter supplied with 68.6mm of irrigation water over 29 days. Simulated volumetric water contents statistically matched those measured using a capacitance soil water probe. Statistical measures (MAE, RMSE, tcal) indicating the correspondence between measured and simulated moisture content were within the acceptable range. The modelling efficiency (E) and the relative efficiency (RE) were in the satisfactory range, except RE at day 19. Simulated daily and cumulative drainage fluxes also matched measured values well. Cumulative drainage flux was 48.9% of applied water, indicating large water losses even under controlled water applications. High drainage losses were due to light texture of the soil and high rainfall (70mm) during the experimental period. Simulated root water uptake was 40% of applied water.The calibrated HYDRUS model was also used to evaluate several scenarios involving nitrate fertigation. The numerical analysis of NO3-N dynamics showed that 25.5% of applied fertilizer was taken up by the orange tree within 15 days of fertigation commencement. The rest of the applied NO3-N (74.5%) remained in the soil, available for uptake, but was also vulnerable to leaching later in the growing season. The seasonal simulation revealed that NO3-N leaching accounted for 50.2% of nitrogen applied as fertilizer, and plant N recovery amounted to 42.1%. The scenario analysis further revealed that timing of a nitrogen application in an irrigation event had little impact on its uptake by citrus in the lysimeter. However, slightly higher NO3-N uptake efficiency occurred when fertigation was applied late in the daily irrigation schedule, or was spread out across all irrigation pulses, rather than being applied early or in the middle. Modelling also revealed that pulsing of irrigation had little impact on nitrate leaching and plant uptake. Applying less irrigation (50% or 75% of ETC) resulted in higher nitrate uptake efficiency. This study showed that timing of water and fertilizer applications to an orange crop can be better regulated to enhance the efficiency of applied inputs under lysimeter conditions.

A general algorithm for automated scheduling of drip irrigation in tree crops

Judicious irrigation necessitates development of technologies that apply the precise amount of water demanded by crops. The goal is to schedule irrigation according to the particular requirements of each orchard and to the variability encountered during the season caused by weather conditions, canopy development and other factors. For supporting a precise and low labour management of irrigation here we propose and depict an algorithm that coordinates seven automatable tasks: (1) estimation of irrigation needs, (2) adaptation to a particular irrigation setup, (3) execution of the schedule, (4) soil and/or plant monitoring, (5) interpretation of sensor data, (6) reaction to occasional events and (7) tuning the model of irrigation needs. This is illustrated with three examples from a peach orchard where a software tool implementing the algorithm was configured to manage irrigation under different strategies. They included two alternative methods for estimating the crop water needs: a typical water balance based on reference evapotranspiration (ETo) and a variation based on the measurement of solar radiation intercepted by the canopy. They also included two types of sensors for feedback: soil water probes and dendrometers, the latter for applying regulated deficit irrigation. The results show that the proposed algorithm provided a common framework that could be embraced under different irrigation strategies to support autonomous control through the season, requiring no more data than those acquired and processed by the same system and enabling some degree of tolerance to failures. Overall, some advantages were the fast response to changes in factors such as weather conditions whose effect is rather predictable. At the same time the algorithm self-adjusted through feedback to variation in orchard-specific factors related with crop development and phenology which would be hard to model. The separation between agro-meteorological and hydraulic concerns in different steps of the algorithm facilitated the adaptation to the particularities of each irrigation setup, simplifying the use of commercial equipment from different manufacturers.

Performance of a New Capacitance Soil Moisture Probe in a Sandy Soil

Rapid population growth and increasing urban demand reduce the availability of water for agriculture in Florida. The water‐holding capacity of sandy soils in the Central Florida Ridge area is very poor (<0.10 m3 m−3). Improved soil water monitoring probes can help growers manage irrigation more efficiently and conserve water. This study evaluated a new soil water probe (ECH2O EC‐5 sensor, Decagon Devices, Pullman, WA) in terms of probe‐to‐probe signal variability, response to fertilizer‐induced salinity, and changes in soil temperature, soil volume sampled, sensitivity to pockets of air or dry soil, and performance in the field. Results were compared with an earlier version of a Decagon probe, the EC‐20. Results indicated that the new probe has several advantages. The EC‐5 was not sensitive to salinity or temperature fluctuations. Probe output change was almost zero when the salinity of the soil was increased by adding fertilizer to a soluble solids concentration of 14 g kg−1 When temperature was changed gradually from 3 to ∼38°C, probe output increased by only about 1%. Soil volume sampled by the probe was about 15 cm3 The change in probe response was negligible when soil cores up to 0.95 cm in diameter near the probe surface were removed. Probes responded well to changes in soil water content in the field. The EC‐5 probe output increased noticeably when bulk density was increased from 1.1 to 1.6 Mg m−3 Probe‐to‐probe output signal and response to bulk density variations can affect the estimation of field water content unless necessary correction factors are utilized. These probes can be useful for monitoring soil water movement, estimating soil water content, and scheduling irrigation.

Design and Field Evaluation of a New Controller for Soil-Water Based Irrigation

A new irrigation controller was developed using readily available components and coupled with an inexpensive dielectric soil water probe. The electronic controller was designed to be easily adapted to existing commercial irrigation systems that currently use time clocks with a pressurized water supply. The total cost of components used in this controller (not including shipping or labor costs) was US$124 including the US$60 sensor. The new device was field tested against other common automatic scheduling methods (fixed timer and variable timer based on historical evapotranspiration) on a drip-irrigated plastic-mulched tomato field in South Florida. The soil water feedback irrigation control with this new device saved up to 74% water while maintaining yields with respect to the typical fixed irrigation schedule rates applied by commercial tomato growers during the winter season in the area. Comparisons with evapotranspiration-based application rates for the area also showed water savings of up to 61%. Although similar savings (up to 79%) were obtained with switching tensiometers, in the gravelly soils of the area these devices are difficult to maintain requiring refilling at least twice a week whereas the soil-water controller required no maintenance throughout the season. The new controller proved reliable and simple to use. It is recommended that the irrigation set-point be validated in the field at the beginning of the season. The study shows that the combined variability of the soil and the water probes resulted in relatively high variability of water application, although the resulting variability in the yield response was less.

Field calibration of an impedance soil water probe for the shallow seedbed across field topography

AbstractImpedance soil water probes enable frequent and non‐destructive determination of soil water status in situations where gravimetric soil sampling is too demanding of time and sampling space. The ThetaProbe is an impedance soil water probe requiring calibration for local soil conditions, because measurement accuracy can be affected by properties of the soil. Often, only a single calibration is performed for an experimental site. An experiment investigating the seedbed to 75‐mm depth across a field topography with variable soil properties was examined to determine which soil properties affected the calibration of the ThetaProbe, and if soil‐specific calibration was required to derive suitable estimates of the water status in the experiment. Experimental factors examined included hillslope aspect, hillslope position, crop residue and soil depth. Soil properties, other than volumetric water content, significantly affecting the probe measurements were bulk density, electrical conductivity and temperature. The probe underestimated soil water at very low water contents, and overestimated soil water at contents greater than 11 m3 m−3, compared with gravimetric measurements. A single calibration, not corrected for hillslope position at a water content of 20 m3 m−3, overestimated water content by 0.02 m3 m−3 in the summit hillslope position and underestimated water content by 0.04 m3 m−3 in the toeslope position. A single calibration, not corrected for soil depth at a water content of 20 m3 m−3, overestimated water content by 0.02 m3 m−3 in the 0‐ to 25‐mm soil layer and underestimated water content by 0.03 m3 m−3 in the 50‐ to 75‐mm layer. The complexity of microsites in a shallow seedbed requires soil‐specific calibration in field experiments containing heterogeneous soil properties.

Comparison of Capacitance‐Based Soil Water Probes in Coastal Plain Soils

Soil water influences infiltration and runoff and consequently water quality. In situ measurements of soil water are critical for understanding hydrologic and water quality processes. Many advances have recently been made in soil water measurement techniques. In particular, instruments for estimating volumetric water content from measurements of soil electrical properties have become common. While the instruments have been shown to be good indicators of relative changes in soil water, questions remain regarding their ability to yield quantitative estimates. Most of these techniques rely on a limited set of calibration equations obtained through laboratory analysis of homogeneous soil materials (i.e., sand, silt, and clay). The accuracy of two capacitance‐based soil water probes was assessed for a range of Coastal Plain soils. The probes measure capacitive and conductive soil properties and relate these to water content through calibration. Calibration curves for three different Coastal Plain soils were developed. Laboratory tests indicate that the probes yield estimates of volumetric water content within ±0.05 cm3 cm−3 of the observed values for these soils. Greater variability was observed in comparisons with field observations. Results indicate that improved equations can be developed through soil‐specific laboratory calibration. The capacitance probes should prove to be useful tools for estimating volumetric water content in these soils. Additional work is required to quantify probe differences and the effects of soil conductivity on the measurements.

Comparison of Capacitance-Based Soil Water Probes in Coastal Plain Soils

Comparison of Capacitance-Based Soil Water Probes in Coastal Plain Soils

Field calibration of a capacitance soil water probe in heterogeneous fields

Soil water research requires methods to perform accurate measurements. A capacitance probe gauge has characteristics that seem to make it an attractive replacement for neutron scatter gauges to measure soil water content, but there is evidence that capacitance systems should be calibrated for individual soils. Laboratory calibrations and many field calibration methods are costly and time-consuming, and controlled conditions and disturbed soil samples do not always reflect field conditions, and thus, they are inadequate for practical use. The objectives of the present study were (i) to test a simple field calibration method for a recently developed capacitive sensor even under highly variable soil texture conditions, and (ii) to validate this approach under various soil moisture conditions. Soil samples were taken 0.5 m from the access tube of the sensor and a whole field calibration and several site-specific calibrations were developed using 10–142 observations per site under different soil water regimes. A regression of soil water content estimated by sensor reading on water content obtained by core sampling showed no significant difference in the slope and intercept of the 1:1 line when the field calibration was applied. However, the precision of the calibration was only considerably increased if the estimations were based on site-specific calibrations developed on at least 35 observations per site. The precision and accuracy of the calibration equations were not affected when data were obtained only under wet or dry soil conditions. The method presented in this paper is a speedy and cheap way to calibrate capacitance probe sensors.

FROM DROUGHT TO FLOOD: CATCHMENT RESPONSES REVEALED USING NOVEL SOIL WATER PROBES

New soil water probes, developed at the Macaulay Land Use Research Institute (MLURI), were used in catchment studies during the transition from drought to flood, revealing insights into both spatial and temporal behaviour of water in the soil profile. Measured soil water content showed that the mineral horizons became progressively wetter upwards from the base of the profile, which was confirmed by linked hydrochemical studies. After severe droughts the amounts of water required to raise soils back to field capacity may have long-term consequences on water abstraction. © 1997 by John Wiley & Sons, Ltd.

FROM DROUGHT TO FLOOD: CATCHMENT RESPONSES REVEALED USING NOVEL SOIL WATER PROBES

New soil water probes, developed at the Macaulay Land Use Research Institute (MLURI), were used in catchment studies during the transition from drought to flood, revealing insights into both spatial and temporal behaviour of water in the soil profile. Measured soil water content showed that the mineral horizons became progressively wetter upwards from the base of the profile, which was confirmed by linked hydrochemical studies. After severe droughts the amounts of water required to raise soils back to field capacity may have long-term consequences on water abstraction.