Marcello Mastrorilli

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.

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.

Using the CERES-Maize model in a semi-arid Mediterranean environment. Evaluation of model performance

The CERES-Maize model was tested in a semi-arid Mediterranean environment during a period of 2 years under three different soil moisture conditions (well-watered and two limited irrigation regimes). In well-watered plots, growth and yield were adequately simulated by the model (differences between simulated values and observations were less than 10%). Results suggest that the absence of air humidity among the model inputs does not limit the CERES-Maize performance, even under dry-air conditions. On the contrary, under mild soil water shortage, CERES-Maize underestimated the leaf area index (LAI) (up to 26% for maximum LAI), above-ground biomass (up to 23%) and grain yield (up to 15%). Mismatches between observations and predictions increased with water stress level (by up to 46, 29 and 23% for maximum LAI, biomass and grain yield, respectively). It is suggested that the functions describing leaf growth and senescence and those calculating the soil water deficit functions should be modified to adapt CERES-Maize to Mediterranean environments.

Daily actual evapotranspiration measured with TDR technique in Mediterranean conditions

Abstract This paper proposes to evaluate the performances of the TDR (Time Domain Reflectometry) technique in a semi-arid region. To achieve this objective a comparison was made on a daily scale for sorghum and maize crops. Their actual evapotranspiration (ET) was measured by two independent methods: soil water balance budget, using soil water content measured by gravimetric and TDR methods and energy balance equation (Bowen ratio). The daily ET values derived from soil water balance budget agreed with the values of ET determined by the Bowen ratio. Results show that in soils without vertical cracks daily ET can be estimated in field by using the TDR technique over a wide range of soil water content.

Water efficiency and stress on grain sorghum at different reproductive stages

Abstract The effects of water stress occurring at various growth stages during the reproductive cycle of grain sorghum were evaluated in open field conditions under a Mediterranean climate. This research was carried out under the same conditions in two steps: (1) assessing the degree of water stress; (2) evaluating the water use efficiency (WUE) and the sensitivity of phenological stages submitted to identical water stress. The first step consists in field calibration of the water stress criterion. During three soil drying cycles it was observed that: (1) the highest stomatal conductance occurred in correspondence with leaf water potential ( Ψ values higher than −1.5 MPa; (2) stomata tended to close when Ψ becomes lower than −1.8 MPa. These values were retained in the second step for monitoring plant water status in four different plots: one never stressed and three stressed at different phenological stages (early flowering, seed-setting and ripening). An evaluation of the sensitivity of phenological stages submitted to identical water stress was obtained by comparing four yield components (above ground biomass, grain yield, 1000 grain weight and seed number) and WUE to those of the well-irrigated crop. The sensitivity was greatest at the early flowering stage. For water saving purposes, these conclusions could be useful for scheduling grain sorghum irrigation.

Salt tolerance of crops according to three classification methods and examination of some hypothesis about salt tolerance

This publication is a complement to a previous publication on salt tolerance classification, using the observations of a long-term experiment on the use of saline water. Three classification methods were compared, based, respectively, on the electrical conductivity of the saturated paste extract, the relative evapotranspiration deficit and the water stress day index. Among the eight crops grown during the experiment, broadbean, soybean and tomato were clearly distinguished by the methods based on the relative evapotranspiration deficit and the water stress day index as more sensitive then durum wheat, maize, potato, sugar beet and sunflower. Their greater sensitivity may be explained by the salt sensitivity of rhizobium bacteria affecting the nitrogen supply, by the degree of osmotic adjustment or by the prolongation of the flowering period.

A modified version of CERES-Maize model for predicting crop response to salinity stress

Abstract A new saline stress index was developed for CERES-Maize, a computer model of maize growth and development, in order to simulate crop response to irrigation with saline water in Mediterranean conditions. Changes from the original model consisted in modifying the estimation of the stress coefficient, which was defined as a function of predawn leaf water potential. The study was carried out at the Mediterranean Agronomic Institute of Bari using a set-up of 30 drainage lysimeters. Linear regression between mean simulated and measured data showed that the model performed well for final grain yield though it tended to underestimate (∼8%) above-ground biomass and maximum leaf area index (LAI). The largest evapotranspiration over-estimations were found early in the growing season immediately after each irrigation event. However, the prediction of seasonal evapotranspiration was generally reasonably good.

Environmental and soil-plant parameters for modelling actual crop evapotranspiration under water stress conditions

Abstract The evapotranspiration of a crop (ET), in every water condition, is modelled starting from the Penman-Monteith combination equation. The model is subdivided into two submodels, the first one takes into account the behaviour of the crop subjected to environmental demands (the atmospheric thermodynamic status); whereas the second submodel depends only on available energy (this second factor is the ‘equilibrum evapotranspiration’). Thus, the final form of evapotranspiration, on a daily scale, is the product of a coefficient dependent on crop water status expressed by means of predawn leaf water potential and the equilibrium ET. A further simplification of the model is introduced substituting to leaf water potential an experimental function of available water in the soil. Model testing was done by comparing the output (ETcalculated) with actual ET measured by means of the energy balance/Bowen ratio method (ETmeasured), in a location in southern Italy, characterized by semi-arid climate. The results show a very good performance of the model for three crops (soybean, grain sorghum and sunflower) in good water status as well as in water stress. Sorghum, ETcalculated = 0.95 ETmeasured (r2 = 0.98); soybean, ETcalculated = 1.00 ETmeasured (r2 = 0.98); sunflower, ETcalculated = 0.93 ETmeasured (r2 = 0.97).