Nader Katerji

Measurement and estimation of actual evapotranspiration in the field under Mediterranean climate: a review

Abstract The Mediterranean regions are submitted to a large variety of climates. In general, the environments are arid and semi-arid with summers characterised by high temperatures and small precipitation. Due to the scarcity of water resources, the correct evaluation of water losses by the crops as evapotranspiration (ET) is very important in these regions. In this paper, we initially present the most known ET measurement methods classified according to the used approach: hydrological, micrometeorological and plant physiological. In the following, we describe the methods to estimate ET, distinguishing the methods based on analytical approaches from the methods based on empirical approaches. Ten methods are reviewed: soil water balance, weighing lysimeter, energy balance/Bowen ratio, aerodynamic method, eddy covariance, sap flow method, chambers system, Penman–Monteith model, crop coefficient approach and soil water balance modelling approach. In the presentation of each method, we have recalled the basic principles, underlined the time and space scale of its application and analysed its accuracy and suitability for use in arid and semi-arid environments. A specific section is dedicated to advection. Finally, the specific problems of each method for correct use in the Mediterranean region are underlined. In conclusion, we focus attention on the most interesting new guidelines for research on the measurement and estimation of actual crop evapotranspiration.

Salinity effect on crop development and yield, analysis of salt tolerance according to several classification methods

Abstract The publication is a synthesis of previous publications on the results of a long-term lysimeter experiment. From 1989 to 1998, the experimental variables were soil salinity and soil type, from 1999 onwards, soil salinity and crop variety. The plant was studied during the whole growing period by measuring the saline stress and analyzing its effect on leaf area and dry matter development and on crop yield. Salinity affected the pre-dawn leaf water potential, stomatal conductance, evapotranspiration, leaf area and yield. The following criteria were used for crop salt tolerance classification: soil salinity, evapotranspiration deficit, water stress day index. The classification according to soil salinity distinguished the salt tolerant group of sugar beet and wheat, the moderately salt sensitive group comprising broadbean, maize, potato, soybean, sunflower and tomato, and the salt sensitive group of chickpea and lentil. The results for the salt tolerant and the moderately salt sensitive groups correspond with the classification of Maas and Hoffman, excepted for soybean. The evapotranspiration deficit criterion was used, because for certain crops the relation between yield and evapotranspiration remains the same in case of drought and salinity. This criterion, however, did not appear useful for salt tolerance classification. The water stress day index, based on the pre-dawn leaf water potential, distinguished a tolerant group, comprising sugar beet, wheat, maize, sunflower and potato, and a sensitive group, comprising tomato, soybean, broadbean, chickpea and lentil. The classification corresponds with a difference in water use efficiency. The tolerant crops show a more or less constant water use efficiency. The sensitive crops show a decrease of the water use efficiency with increasing salinity, as their yield decreases stronger than the evapotranspiration. No correlation could be found between osmotic adjustment, leaf area and yield reduction. As the flowering period is a sensitive period for grain and fruit formation and the sensitive crops are all of indeterminate flowering, their longer flowering period could be a cause of their greater sensitivity. The tolerant group according to water stress day index can be divided according to soil salinity in a salt tolerant group of sugar beet and wheat and a moderately sensitive group, comprising maize, sunflower and potato. The difference in classification can be attributed to the difference in evaporative demand during the growing period. The sensitive group according to water stress day index can be divided according to soil salinity in a moderately sensitive group, comprising tomato, soybean and broadbean, and a salt sensitive group of chickpea and lentil. The difference in classification can be attributed to the greater salt sensitivity of the symbiosis between rhizobia and grain legume in the case of chickpea and lentil.

Salt tolerance classification of crops according to soil salinity and to water stress day index

The observations of a long-term experiment on the use of saline water were used to compare the crop tolerance to salinity. Salinity affected significantly yield, evapotranspiration, pre-dawn leaf water potential and stomatal conductance. The higher the salinity, the lower the yield, evapotranspiration, pre-dawn leaf water potential and stomatal resistance. The crop classification, based on soil salinity, corresponds with the classification of Maas and Hoffman: sugarbeet and durum wheat as salt tolerant, broadbean, maize, potato, sunflower and tomato as moderately salt sensitive. The difference with respect to soybean, classified as moderately salt sensitive instead of moderately salt tolerant can be ascribed to difference in variety. Weather conditions affected strongly the salt tolerance of broadbean. The water stress day index was also used for salt tolerance classification. According to this method, maize, sunflower and potato were included in the same salt tolerant group as sugarbeet and durum wheat. The previous classification of maize and sunflower as moderately sensitive is caused by the fact that these crops are grown during a period of higher evaporative demand than when sugarbeet and durum wheat are grown. The change of potato from moderately sensitive to salt tolerant may be ascribed to its shallow root system.

Osmotic adjustment of sugar beets in response to soil salinity and its influence on stomatal conductance, growth and yield

Abstract Sugar beets were grown in tanks filled with loam and clay, and were irrigated with waters of three different levels of salinity. Osmotic adjustment was determined by analyzing the pressure-volume curves at three growth stages. Sugar beets showed osmotic adjustment in two ways: with their phenological development and towards salinity. Owing to the latter adjustment sugar beets are able to maintain the turgor potential at the same value for lower values of the leaf water potential, to maintain stomatal conductance and photosynthesis and finally their production under severe water stress. Salinity affected the pre-dawn leaf water potential, stomatal conductance and evapotranspiration on both soils, but leaf area and yield only on loam. Soil texture affected stomatal conductance, evapotranspiration, leaf area and yield. As the latter was about 35% lower on clay, whereas the evapotranspiration decreased 10 to 15%, the water use efficiency was about 25% lower on clay compared with loam.

Effect of salinity on yield and nitrogen uptake of four grain legumes and on biological nitrogen contribution from the soil

Abstract Broadbean, chickpea, lentil and soybean were grown in a tank experiment and irrigated with waters of three different levels of salinity. The nitrogen uptake of the crop was determined from the yield of aereal biomass and grain, and the corresponding nitrogen contents. The biological contribution of the soil from nitrogen fixation and transformation of organic nitrogen was calculated as difference between the plant uptake and the amount supplied by fertilizer and irrigation minus the loss by drainage. Soil salinity affected crop yield, crop total nitrogen uptake and the nitrogen contribution of the soil. The latter decreased in % of plant uptake at increasing salinity and also decreased stronger than the plant uptake, pointing to a salinity effect on the mineral nitrogen production by biological activity in the soil through nitrogen fixation and transformation of organic nitrogen. A salinity effect on nitrogen fixation could explain, at least partly, the salt sensitivity of grain legumes.

Productivity and water use efficiency of sweet sorghum as affected by soil water deficit occurring at different vegetative growth stages

The growth and production of sweet sorghum [Sorghum bicolor (L.) Moench] crops under semi-arid conditions in the Mediterranean environment of southern Italy are constrained by water stress. The eVects of temporary water stress on growth and productivity of sweet sorghum were studied during three seasons at Rutigliano (Bari, Italy). The aim of this research was to evaluate the sensitivity of phenological stages subjected to the same water deficit. In a preliminary study it was observed that stomata closed when pre-dawn leaf water potential (Y b ) became lower than ’0.4 MPa. This criterion was used in monitoring plant water status in three diVerent plots: one never stressed and two stressed at diVerent phenological stages (‘leaf ’ and ‘stem’) when mainly leaves or stems were growing, respectively. An evaluation of the sensitivity of phenological stages subjected to identical water stress was obtained by comparing the above-ground biomass and WUE of drought crops with those of the well-irrigated crop (up to 32.5 t ha’1 of dry matter and 5.7 g kg’1). The sensitivity was greatest at the early stage (‘leaf ’), when a temporary soil water stress reduced the biomass production by up to 30% with respect to the control and WUE was 4.8 g kg’1 (average of three seasons). These results help quantify the eVects of water constraints on sweet sorghum productivity. An irrigation strategy based on phenological stage sensitivity is suggested.

Effect of saline water on soil salinity and on water stress, growth, and yield of wheat and potatoes

Abstract Wheat and potatoes were grown in tanks filled with loam and clay and irrigated with water of three different levels of salinity and, for the wheat, with two irrigation regimes. A combination of soil water sampling and salt balance was used to study the development of soil salinity and the composition of the soil water. This revealed an increase in adsorbed sodium, a decrease in adsorbed calcium and magnesium, and precipitation of a mixture of calcium and magnesium carbonate. Predawn leaf-water potential and stomatal conductance can be used as parameters for water stress, and show good coherence with growth and yield. That potatoes are more sensitive to water stress than wheat was reflected by greater differences in leaf-water potential and stomatal conductance, and a more severe yield decrease. Soil, salinity and water regime affect water stress, growth, and yield. The water efficiency of wheat and potatoes was not affected by soil and salinity.

Some plant factors controlling evapotranspiration

Stomatal conductance varies within a leaf, between leaves in a canopy and between layers. It depends primarily on light and it is possible to derive a canopy conductance, gc, by summing the stomatal conductances of leaves of all layers. This may be done by measurements or by using a simple model. Such a calculated canopy conductance can be used successfully in the Penman-Monteith formula to predict the evapotranspiration of a closed canopy well supplied with water. For incomplete canopies, soil and plant evaporation require different treatments. The ratio EcEo of canopy transpiration to open water evaporation varies roughly in proportion with the fraction of soil covered by vegetation, while the ratio EsEo of soil evaporation to Eo is controlled both by net radiation at the soil surface and surface soil moisture. Soil water limitation may be modelled by making EcEo a function of soil water reserve or through a variable stomatal conductance, gs. In the latter case, gs may be related to either soil water potential or leaf water potential, which depends on transpiration and resistance to liquid water flow through the plant. Such resistance is shown to be relatively conservative at the canopy level, but its usefulness for predicting evapotranspiration is debatable since a part of stomatal closure is now attributed to hormonal control.

Effect of salinity on emergence and on water stress and early seedling growth of sunflower and maize

Abstract To study the effect of salinity on the emergence and early seedling growth of sunflower and maize, experiments were conducted in pots filled with sandy clay and sandy loam. The experiments consisted of a control and four saline water qualities with chloride concentrations of 15, 30, 45, and 60 meq/l. The emergence of sunflower and maize were affected by salinity. Soil texture did not affect the emergence. During early seedling growth, salinity and soil texture affected the development of the seedlings that showed symptoms of water stress in the form of lower leaf water potential, stomatal conductance, and evapotranspiration. The higher the salinity, the lower the leaf area and the dry matter production. Leaf, stem, and root showed an almost similar growth reduction due to salinity. Seedlings on sandy loam were more affected by water stress than those on sandy clay.

Effect of salinity on water stress, growth, and yield of maize and sunflower

Abstract Maize and sunflower were grown in tanks filled with loam and clay, and were irrigated with water of three different levels of salinity. Predawn leaf-water potential and stomatal conductance were used as parameters for water stress. The predawn leaf-water potential of maize was higher than that of sunflower, but the effect of salinity and soil texture on the predawn leaf-water potential was the same for both crops. The stomatal conductance of sunflower was much higher and more severely affected by salinity and soil texture than the stomatal conductance of maize. Although salinity had a more serious effect on the development of leaf area and canopy dry matter of sunflower, its effect on evapotranspiration and grain yield was the same for both crops. Soil texture had a stronger effect on the development of leaf area and canopy dry matter of sunflower, which also appeared in the evapotranspiration and grain yield, indicating that sunflower is more sensitive to drought than maize.