1,721,159 research outputs found
Discussion of “Laboratory and field calibration of the Diviner 2000 probe in two types of soil” by J. Haberland, PhD, R. Galvez, C. Kremer, PhD, and C. Carter.
Full text linkThe authors deal with the quite interesting and actual problem of Diviner 2000 capacitance probe calibration and present some field and laboratory data obtained on two different layers (0-0.26 cm and 0.26-0.50 cm) of the same soil profile, characterized by different textural class. The importance of site-specific calibration of sensors used to monitor soil or plant water status assumes a particular relevance in semi-arid environments
where the application of precision irrigation represents an appropriate management strategy aimed to achieve
high values of water use efficiency (Cammalleri et al., 2013). Moreover in clay soils, physical properties are
strongly influenced by soil water content (Provenzano et al., 2013), so that the correct measurement of this
variable plays a key role to increasing crop yield and preserving water.
However, these discussers would focus on some significant points to be corrected in the manuscript and some others that AA. should have been specified in the methodology and considered in the final discussion,
as following specified, for the benefit of potential readers.
The need to install adequately the access tube, aimed to ensure the contact between the tube and the
surrounding soil, is not only to avoid preferential flow of water down the walls of the tube, as considered in
the paper, but also to reduce air gap around the tube and to avoid rough measurements of scaled frequency,
used to estimate soil water contents, whose values depend on the mutual proportion of soil, water and air in the soil volume investigated by the sensor.
With reference to the second part of eq. (2) it is necessary to precise that the function w(SF) correctly results
Indirect estimation of calibration equation parameters for Sentek Diviner 2000 capacitance probe by means of soil physical properties
Full text linkMeasurements of soil water content (SWC) are often used for irrigation scheduling. Accurate monitoring of SWC is
necessary, for example, to identify the exact irrigation timing and the amount of water volume to supply according
to the crop requirement.
The use of capacitance probes, measuring the apparent soil dielectric permittivity, indirectly related to soil water
status, have been increasing during the last decade, as proved by the numerous researches carried out to determine,
for different soil types, site-specific calibration relationships between SWC and the scaled frequency (SF) measured
by the sensor. However, for swelling/shrinking clay soils, there is a lack of knowledge on how the changes of
soil bulk density associated to variations of soil water content influence the apparent dielectric permittivity and
therefore the sensor calibration relationship, as a consequence of the different contribute that soil, water and air,
have on the measure provided by the sensor.
The main objectives of the work are i) to determine the site specific calibration equations for a Sentek Diviner 2000
capacitance probe for soils characterized by different texture, ii) to investigate on the effects of soil bulk density
and its variability with soil water content, on the calibration equation and iii) to proceed to the indirect estimation
of calibration parameters by means of easily-measurable soil physical properties.
Experiments were carried out on nine different soils collected from Sicilian irrigated area, characterized by a clay
percentage ranging between 9% and 45%. Undisturbed soil samples (25 cm diameter and 25 cm height), allowed to
determine, for each soil, the corresponding site-specific calibration equation. On the other hands, samples having
the same dimensions, but filled with sieved soil and compacted at two different bulk densities ( b), were used
to investigate on the effects of soil texture and bulk density on the measured SF. On each undisturbed or sieved
sample and for all the investigated soils, the shrinkage characteristic curve, b(U) and the U(SF) relationship were
contextually determined.
The experiments on sieved soil samples, allowed to verify that the scaled frequency measured by the sensor also
depends on b. According to this result, the generally used calibration equation was modified and a new empirical
model U(SF, b), introducing the relationship b(U) as a factor, was proposed. Of course, for swelling/shrinkage
clay soil the suggested calibration equation results implicit, if considering that b is also a function of U.
The experiments also allowed to verify that parameters of the calibration equation depend on soil clay percentage
and then to identify empirical relationships for their estimation, that were finally validated by using measurements
acquired on undisturbed soil samples and some data collected by the literature
ASSESSING FAO-56 MODEL TO ESTIMATE TABLE OLIVE WATER CONSUME UNDER SOIL WATER DEFICIT CONDITIONS
No full textAgro-hydrological models can be considered an economic and simple tool to quantify crop water requirements. In the last two decades, agro-hydrological physically based models have been developed to simulate mass and energy exchange processes in the soil-plant-atmosphere system. Although very reliable, due to the high number of required variables, simplified models have been proposed as simple tools to quantify crop water consumes. The main aim of the paper is to assess, for a Sicilian orchard of table olive, the suitability of FAO-56 agro-hydrological model to estimate the crop transpiration under soil water deficit conditions. The model validation is carried out by means of measurements of sap-flow and soil water contents, acquired during three years of field observations. An amendment of the model is suggested in order to take into account the water stress function and the soil water uptake ability as experimentally evaluated. The results show that the modified model improves the estimation of crop transpiration and soil water content, considered that the associated RMSEs resulted higher than the corresponding values obtained with the original version of the mode
Discussion of "modeling Approaches for Determining Appropriate Depth of Subsurface Drip Irrigation Tubing in Alfalfa" by Rocio Guadalupe Reyes-Esteves and Donald C. Slack
No full textPerformance di impianti per la microirrigazione mediante misure di uniformità ed efficienza di distribuzione.
No full textIl lavoro si propone di valutare, attraverso una indagine di campo, la performance di tre diverse tipologie di impianto per la microirrigazione utilizzate su parcelle coltivate a vigneto. Nelle prime due tipologie di impianto l’erogazione avviene mediante gocciolatori e spruzzatori posizionati al disopra del piano di campagna, mentre nella terza le linee erogatrici sono state poste a circa 40 cm al disotto del piano di campagna, in prossimità dell’apparato radicale delle piante
Analytical Approach Determining the Optimal Length of Paired Drip Laterals in Uniformly Sloped Fields
No full textMicroirrigation plants, if properly designed, allow for water use efficiency to be optimized and high values of emission uniformity to be obtained in the field. Disposing paired laterals, for which two distribution pipes extend in opposite directions from a common manifold, can contribute to reducing the initial investment cost that represents a limiting factor for small-scale farmers of developing countries where in the last decade, the diffusion of such irrigation systems has been increasing. The objective of this paper is to propose an analytical approach to evaluate the maximum lengths of paired drip laterals for any uniform ground slope, respecting the criteria to maintain emitter flow rates or the corresponding pressure heads within fixed ranges in order to achieve a relatively high field emission uniformity coefficient. The method is developed by considering the motion equations along uphill and downhill sides of the lateral and the hypothesis to neglect the variations of emitters’ flow rate along the lateral as well as the local losses due to emitters’ insertions. If for the uphill pipe, the minimum and the maximum pressure heads occur at the upstream end and at the manifold connection, respectively, on the downhill side, the minimum pressure head is located in a certain section of the lateral, depending on the geometric and hydraulic characteristics of the lateral, as well as on the slope of the field; a second relative maximum pressure head could also exist at the downstream end of the pipe. The proposed methodology allows in particular the number of emitters in uphill and downhill sides of the lateral to be determined separately, and therefore, once fixing emitter’s spacing, the length of the uphill and downhill laterals and the position of the manifold. Applications and validation of the proposed approach, considering different design parameters, are finally presented and discussed
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Detecting crop water requirement indicators in irrigated agroecosystems from soil water content profiles: An application for a citrus orchard
No full textMost perennial crops sensitive to water scarcity, such as citrus, can benefit from efficient water management, which allows for reduced water consumption while increasing crop production on a long-term basis. However, when implementing water-saving strategies, it is necessary to monitor soil and/or plant water status in order to determine crop water demand. A plethora of devices providing indirect measurements of volumetric soil water content, such as the “drill and drop” multi-sensors probes (Sentek, Inc., Stepney, Australia), have been developed over the last decade. The objective of the paper was to analyse time-series of soil water content profiles and meteorological data collected in an adult citrus orchard over three years of field observations (2017–2020) in order to estimate actual crop evapotranspiration and derive crop coefficients. Simultaneous measurements of sap fluxes also allowed for the estimation of the basal crop coefficient, Kcb, used as a control variable. The temporal dynamics of soil water content profiles following rainfall or irrigation events provided information on soil evaporation, root water uptake, and actual crop transpiration. After soil wetting events, in particular, it was possible to recognize patterns of actual crop evapotranspiration similar to those detected with sap flow sensors. The knowledge of actual crop evapotranspiration at the daily time-step, in conjunction with the corresponding reference crop evapotranspiration, allowed for appropriate estimations of the crop coefficient associated with the various development stages. The proposed method provided interesting insights into the dynamics of root water uptake and crop evapotranspiration of the studied citrus orchard, and it represents a promising tool for precise irrigation scheduling in other agroecosystems
Modelling eco-physiological response of table olive trees (Olea europaea L.) to soil water deficit conditions
No full textThe knowledge of crop response to water stress is crucial to predict transpiration reductions under limited soil water conditions and for a rational scheduling of irrigation.
In order to assess whatever water stress model, it is necessary to estimate critical thresholds of soil water status, below which plant transpiration starts to decrease.
The main objective of the work is to identify the shape and to determine the parameters of table olive orchards (Olea europaea, var. Nocellara del Belice) water stress function, assessed according to relative transpiration or leaf/stem water potential.
In order to assess different water stress functions describing the eco-physiological field response to soil water status, an experimental campaign was carried out in a farm located in South-West coast of Sicily. Meteorological data and soil and crop water status were monitored during irrigation seasons 2008 and 2009.
A value of soil matric potential of about −40 m was identified as the threshold below which actual transpiration decreases with decreasing soil water content. For values of soil matric potential higher than the critical threshold, actual transpiration resulted almost constant. A similar behavior was observed when the xylematic leaf/stem water potentials were used to quantify the crop water stress. Investigation also showed that the non-linear models better reproduced the initial phase of the transpiration reduction process; for the examined crop, in fact, convex shape models, typical of xerophytes, better reproduce the reductions of actual transpiration under the soil water deficit conditions recognized in the field
- …
