Review. Use of psychrometers in field measurements of plant material: accuracy and handling difficulties

Abstract

For years, one of the major concerns of agronomists has been the study of how variations in the crop environment can affect proper crop development. A variety of factors must be considered, including factors such as plant genetics, climatic conditions or soil, and factors directly dependent on man such as technology or labour. In the search for sustainable development, all these factors must coexist in perfect harmony in order AbstractThe determination of leaf water potential is useful in the establishment of irrigation guidelines for agricultural crop management practices and requires the use of various methods, among which thermocouple psychrometers (TCP). TCP have been widely used for this purpose. However, the psychrometric technique is complex and difficult to understand and the instrumentation required is difficult to handle. For this reason, a profound knowledge of the different aspects involved in the technique -which have not been clearly explained in the literature-is required. This paper reviews a number of research areas of TCP and focuses on three very specific fields: a) main applications of phsychrometry in field studies; b) determination of the measurement accuracy of psychrometric equipment, accuracy per se and accuracy tested against alternative methods; c) main errors and handling difficulties of TCP in the field. Research in these areas provides an updated overview of TCP as a method for determining water relations in plant material that will contribute criteria to select the most suitable technique according to the type of plant material and the purpose of the research and will highlight the types of instruments, accuracies and errors that have detrimental effects on measurements.Additional key words: hygrometric technique; irrigation; isopiestic technique; pressure chamber; psychrometric technique. ResumenRevisión. Aplicación de la psicrometría en campo a material vegetal: precisión y dificultades de manejo La determinación del potencial hídrico foliar es muy útil en el establecimiento de directrices de riego en las prácti-cas de manejo agrícola de los cultivos, requiriéndose del uso de diferentes métodos como los psicrómetros termopar (TCP). Los TCP han sido ampliamente utilizados. Sin embargo, se trata de una técnica compleja de difícil manejo. Por lo tanto, se requiere un profundo conocimiento de los diferentes aspectos involucrados en la técnica, que no han sido claramente explicados en los diferentes estudios publicados. Este artículo revisa una serie de líneas de investigación de los TCP. Estas áreas de investigación se han centrado en tres campos muy específicos: a) principales actuaciones en campo empleando la psicrometría; b) especificación de la precisión de los equipos, per se y frente a otras metodologías alternativas; c) principales errores y dificultades de manejo en campo de los psicrómetros. La investigación en esta área permitirá aportar una visión actualizada sobre los TCP como método de determinación de relaciones hídricas en material vegetal, aportando criterios de sele...

Plant-Based Methods for Irrigation Scheduling of Woody Crops

“…Although difficult to use in the field, mainly because of daily changes in air temperature, some TCP instruments can be used under field conditions [50,51]. Recently, a new type of small tensiometer has been developed for the measurement of water potential in plants.…”

Impact of water stress and nutrition on Vitis vinifera cv. ‘Albariño’: Soil-plant water relationships, cumulative effects and productivity

“…At the plant level, leaf-water stress indices have been quantified according to the plant's water potential at different times of the day, such as predawn or midday, or in different plant parts, such as the leaf or stem. Leaf-water potential is easily determined using a Scholander pressure chamber (Scholander et al, 1965) or, more recently, with a water activity meter (Martínez et al, 2011a(Martínez et al, , 2012a(Martínez et al, and 2013b. The integration of long-term leaf-water potential values into a single value was introduced by Myers (1988).…”

“…The starting irrigation is applied based on previous experience and weather conditions for that year. Irrigation is performed to support nutrient absorp- (Gee et al, 1992;Martínez et al, 2011a) according to the methodology proposed by Martínez et al (2013b). The technique for measuring leaf-water potential with a water activity meter implies the measurement of leaf disks with three repetitions (n=3) per plant, performed in sequential measurements by the measuring equipment, having previously sanded the leaves to eliminate the cuticle.…”

Leaf turgor pressure in maize plants under water stress

“…The monitoring of water conditions in plants is important for determining the optimal timing of irrigation, thus avoiding losses arising from lack of water. To this end, indicators of plant water status through measurement of water potential of their organs (mainly leaves) have been frequently used by means of either a method based on equilibrium vapor pressure (psychometric/thermocouple techniques) (Martinez et al, 2011) or on pressure balance (pressure chamber) (Boyer, 1967); linear transducers to determine inference from variation in leaf thickness (Seelig et al 2012) and/or microdendrometry technique to assess variation in trunk/stem diameter (Simmoneau et al, 1993;Junjittakarn et al, 2011) are also used. Despite all these alternatives for evaluating plant water status, studies in this research field present problems involving the representativeness of these stress indicators based on the plant itself , especially those that use inferences from physiological responses.…”