The tolerance of perennial fruit crops to salinity is usually determined by analyzing tree performance in relation to EC or NaCl concentration in the soil and/or irrigation water or in relation to the period during which the plants were grown under salinity conditions. In response to these conditions, toxic ions accumulate in the plant overtime, but very few studies have sought to correlate ion concentration directly to tree vegetative and/or reproductive performances. We investigated the utility of a direct short-term approach that involved "loading" Ziziphus jujuba trees with different levels of NaCl and determining the correlation between the accumulation of specific toxic ions in the leaves, flowers and roots (Na+ and Cl-) and the change in tree vegetative and reproductive performance. Z. jujuba cultivar 'Ben-Li' trees planted in pots were irrigated with four salinity levels: 13.2, 31.7 and 61.9 mM NaCl and tap water (1.6 mM Na+ and 1.1 mM Cl-) as control. The salinity threshold for normal growth and flowering was found to be 0.40% Na+ and 2.68% Cl- in leaves (% of dry weight), 0.27% Na+ in roots, and 0.10% Na+ and 0.52% Cl- in flowers. Na+ accumulation was correlated with impairment in six of the seven growth and flowering traits tested, while Cl- was found to be correlated to only three of these seven traits, suggesting that for the salinity range tested Na+ is the more toxic ion for Z. jujuba trees. The present study shows that the rise in toxic ion concentrations in the plant tissues correlates with changes in flowering and tree growth, thereby making it possible in the short term both to determine the salinity threshold above which there is a reduction in yield and to predict in the longer term changes in tree performance as a function of ion accumulation. (C) 2014 Elsevier B.V. All rights reserved.

The effect of atmospheric water vapor (AV) on plants has mostly been neglected in climate impact studies. The objectives of this study were to determine the effect of AV on photosynthesis (Pn), dry matter production (DM), transpiration (Tr), leaf conductance (gl) and water use efficiency (WUE), in climate controlled chambers. The relative humidity (RH) was held near 30, 60, and 85%. DM and WUE increased with RH. δDM/δRH ~ 0.3 from 30% to 60% and ~2.2 from 60% to 85%, δWUE/δRH ~0.2 for all RH's. The improved WUE at a rate of 0.2 units for each percent of increased RH resulted from a synergy between larger gl and lower Tr at high RH. This conclusions carries a bleak message to dry regions.

The objective of this study was to develop a method to determine root mean square (RMS) height h of the surface roughness using single-channel data from the European remote-sensing satellite-2 (ERS-2) synthetic aperture radar (SAR) for known soil texture and water content. Accordingly, a new equation for the determination of h was obtained, which required combining two models: a semi-empirical model of vertically co-polarized mode backscattering coefficient sigma(0)(nu nu) for bare soil; a semi-empirical model for the real part of dielectric constant e and the empirical equation deriving the roughness correlation length I from h. The equation allowed calculating h for ERS-2 SAR data on natural bare smooth flat sandy and loessy areas of the Negev desert (Israel) for the dry, wet and artificially wetted conditions. It was found that the roughness of soil was typically small (h < 0.5 cm) and remained constant throughout the whole annual wetting cycle. Corresponding formulas were developed and applied for the determination of absolute and relative errors of retrieved h. It was shown that the relative error in retrieving of h was almost independent of its value. The values of h obtained from ERS-2 SAR data showed acceptable correlation with the ground measurements. (C) 2012 Elsevier Ltd. All rights reserved.

The CAM photosynthetic-pathwayplant Hylocereus undatus) was introduced to the Israeli Negev Desert as a fruit crop with a high water-use efficiency (WUE). Its photosynthetic rate (P-N) was measured continuously in the field with a "photosynthesis monitor" (PM48 made in Israel). The system was closed for a short (2 minutes) sampling period and opened for the rest of the time (28 minutes), when undisturbed gas exchange occurs. Time Domain Reflectometry (TDR) was used to measure evapotranspiration (ET). Quasi stem conductance (QC; kPa(-1)) was determined as the ratio between relative sap flow and VPD, representing the ratio between transpiration and its driving force. Water (equivalent to 2 liters/plant-day) was applied by a drip system every other day. Withholding water decreased PN by about 10% per day. Fluctuating maximal PN reflected the rapid changes in soil water status of the sandy soil. Sinusoidal fluctuations of QC and PN reached their maximum at night. They were zero during daytime when ET was 3.2 mm (60% of potential ET). Due to the very low QC during the daytime, most ET was attributed to evaporation from the soil rather than to transpiration. The low ET and the high of H. undatus resulted in a WUE that was several times higher than the WUE of other fruits crops in the Negev Desert.

Four temperature treatments were studied in the climate controlled growth chambers of the Georgia Envirotron: 25/20, 30/25, 35/30, and 40/35 °C during 14/10 h light/dark cycle. For the first growth stage (V3-5), the highest net photosynthetic rate ( P N ) of sweet corn was found for the lowest temperature of 28–34 µmol m −2 s −1 while the P N for the highest temperature treatment was 50–60 % lower. We detected a gradual decline of about 1 P N unit per 1 °C increase in temperature. Maximum transpiration rate ( E ) fluctuated between 0.36 and 0.54 mm h −1 (≈5.0–6.5 mm d −1 ) for the high temperature treatment and the minimum E fluctuated between 0.25 and 0.36 mm h −1 (≈3.5–5.0 mm d −1 ) for the low temperature treatment. Cumulative CO 2 fixation of the 40/35 °C treatment was 33.7 g m −2 d −1 and it increased by about 50 % as temperature declined. The corresponding water use efficiency (WUE) decreased from 14 to 5 g(CO 2 ) kg −1 (H 2 O) for the lowest and highest temperature treatments, respectively. Three main factors affected WUE, P N , and E of Zea : the high temperature which reduced P N , vapor pressure deficit (VPD) that was directly related to E but did not affect P N , and quasi stem conductance (QC) that was directly related to P N but did not affect E . As a result, WUE of the 25/20 °C temperature treatment was almost three times larger than that of 40/35 °C temperature treatment.

Leafy vegetables (especially lettuce) obtained through the summer in Israel suffer leaf burns, caused by both high temperatures and low air humidity. In order to improve products quality, we tested methods to reduce the number of high temp. hours by pulses of water spraying over the canopy in order to obtain simultaneous direct evaporative cooling and increased humidity. The treatments did not reduce much the average temperatures of the air, but canopy temperature and humidity at the close vicinity of the plants was affected. Most of the energy entering the greenhouse is absorbed by the plant and most of it removed as a latent heat. This cooling mechanisms limit plant transpiration so that part of the extra water application for cooling is compensated.

Four temperature treatments were studied in the climate controlled growth chambers of the Georgia Envirotron: 25/20, 30/25, 35/30, and 40/35 °C during 14/10 h light/dark cycle. For the first growth stage (V3-5), the highest net photosynthetic rate ( ) of sweet corn was found for the lowest temperature of 28–34 µmol m s while the for the highest temperature treatment was 50–60 % lower. We detected a gradual decline of about 1 unit per 1 °C increase in temperature. Maximum transpiration rate () fluctuated between 0.36 and 0.54 mm h (≈5.0–6.5 mm d) for the high temperature treatment and the minimum fluctuated between 0.25 and 0.36 mm h (≈3.5–5.0 mm d) for the low temperature treatment. Cumulative CO fixation of the 40/35 °C treatment was 33.7 g m d and it increased by about 50 % as temperature declined. The corresponding water use efficiency (WUE) decreased from 14 to 5 g(CO) kg(HO) for the lowest and highest temperature treatments, respectively. Three main factors affected WUE, , and of : the high temperature which reduced , vapor pressure deficit (VPD) that was directly related to but did not affect , and stem conductance (QC) that was directly related to but did not affect . As a result, WUE of the 25/20 °C temperature treatment was almost three times larger than that of 40/35 °C temperature treatment.

The effects of three irrigation salinity levels (1.8, 3.3, and 4.8 dS/m) on ion accumulation and relative turgidity of Cabernet Sauvignon (Vitis vinifea) grapes on 'Rugerri' and 'Salt Creek' rootstocks were studied in order to introduce more saline water in the Negev Desert of Israel. Leaf samples were taken four times during the summer of 1997 and analyzed for total diffusible ions, which included sodium (Na), calcium (Ca), potassium (K), and magnesium (Mg), and for soluble ions, which included zinc (Zn) and manganese (Mn). Quality and quantity of yield were also measured. The lowest relative turgidity, 0.8, was measured at ECi (electrical conductivity of irrigation water) 4.8 dS/m, which decreased with time to 0.75 for all treatments. The Na/K ratio indicated relative sodium accumulation. It increased fast with time from about 0.1 to 1.4 under high salinity and more slowly, from 0.1 to 0.5, under the low-salinity treatment. Average yield of fresh berries under all treatments (except one) ranged between 8.0 and 8.5 kg/vine under the respective saline and fresh-water irrigation. This difference was not significant, but in view of the first-year experiment this result should be regarded as provisional. The juice quality criteria, as determined by the production of total soluble solids (TSS) pH(2), improved from 321 to 288, indicating low acidity under the saline treatment and higher acidity under the non-saline treatment. The ratio of TSS/acidity, which changed slightly from 34 to 32, also indicated a moderate reduction in acidity under saline conditions, especially under the 'Ruggeri' rootstock. Thus, it was concluded that (a) by the use of saline water the quality of the berries may be improved, (b) 'Ruggeri' rootstock was less affected than 'Salt Creek' by salinity in both quantity and quality of yield, and (c) relative sodium (Na) content in the lamina and the petiole increased with time during the growth period while relative turgidity declined, indicating a possible accumulation of toxic ions over time.

Soil, water, atmosphere and plant (SWAP) model simulates deterministic transport of water and solutes, incorporating a semi-analytical sink function. It enables one to simulate detailed (SAWPd) or simple (SWAPs) crop growth patterns in response to flow patterns in the root zone. The objectives of this study were to evaluate the ability of SWAPd to account for various salinity effects in grapevines under arid conditions, and to compare results from SWAPd and SWAPs growth models. A unique approach in our study was to use the same crop parameters for fresh and saline water while changing only the salinity of the irrigation water. We tested the effect of three salinity treatments (1.8, 3.3 and 4.8dSm−1) on production parameters of grapevine. Vines in the fresh water treatment benefited from the better water quality in that they used water more efficiently than in the other treatments. Three objective criteria were used to test the validity of the two models. These were standard error of model estimation (SEE), root mean square error (RMSE) and the index of agreement (IoA). With respect to the measured variables SEE (expressed as percent of the maximal value) was 5% for 1.8dSm−1 treatment and 11% for 4.8dSm−1 treatment. RMSE was 7 for 1.8dSm−1 treatment and 15% for 4.8dSm−1 treatment. IoA was close to 1. It varied between a minimum of 0.8 for SWAPs to a maximum 0.99 for transpiration calculated by SWAPd for low salinity conditions, indicating acceptable agreements between the simulated and measured results. These simulated results were obtained when water quality was the only variable and hence they indicated the ability of SWAP's salinity models to generate realistic responses to salinity. In all calculations higher transpiration and LAI were simulated by SWAPd than by SWAPs. The deviations (SEE and RMSE) of SWAPs from the measured values were about 4% larger than the deviations of the values simulated by SWAPd. It probably resulted from the more realistic detailed model, which contains many more growth parameters than SWAPs that requires only LAI. The higher simulated transpiration by SWAPd model affected the differences in the entire water regime. For example, SWAPs simulated higher water content than SWAPd because less water was extracted from its soil profile by transpiration. It was concluded that for the first time SWAPd (and to a certain level also SWAPs) was validated for grapevine under saline conditions.

Net CO2 uptake rates (P N) were measured for the vine cacti Hylocereus undatus and Selenicereus megalanthus under relatively extreme climatic conditions in Israel. Withholding water decreased rates and the daily amount of CO2 uptake by about 10 % per day. Compared with more moderate climates within environmental chambers, the higher temperatures and lower relative humidity in the field led to a more rapid response to drought. The upper envelopes of scatter diagrams for P N versus temperature for these Crassulacean acid metabolism species, which indicate the maximal rates at a particular temperature, were determined for both night time CO2 uptake in Phase I (mediated by phosphoenolpyruvate carboxylase, PEPC) and early morning uptake in Phase II (mediated by ribulose-1,5-bisphosphate carboxylase/oxygenase, RuBPCO). As stem temperature increased above 13 °C, the maximal P N increased exponentially, reaching maxima near 27 °C of 12 and 8 μmol m−2 s−1 for Phases I and II, respectively, for H. undatus and 6 and 4 μmol m−2 s−1, respectively, for S. megalanthus. Based on the Arrhenius equation, the apparent activation energies of PEPC and RuBPCO were 103 and 86 kJ mol−1, respectively, for H. undatus and 77 and 49 kJ mol−1, respectively, for S. megalanthus, within the range determined for a diverse group of species using different methodologies. Above 28 °C, P N decreased an average of 58 % per °C in Phase I and 30 % per °C in Phase II for the two species; such steep declines with temperature indicate that irrigation then may lead to only small enhancements in net CO2 uptake ability.

A scatterometer operating in P-band at 441 MHz was used to estimate soil water content. This letter describes encouraging results of experiments that were undertaken in Israel at Yotvata and Ashalim experimental farms. The soil water saturation percent of the entire wetting and drying cycles created through irrigation of sandy agricultural soils were retrieved using the scatterometer, which yielded good agreement with gravimetric measurements of soil water content demonstrating that P-band provides relatively unambiguous estimates of the soil water saturation percent.

We report the use of the microwave remote sensing as a technique with great potential for the mapping of subsurface properties including the monitoring of soil water conditions. Remote sensing experiments with microwave instrumentation were conducted in the Negev desert in Israel. The remote sensors used were a P-band ( 68 cm, 441 MHz) scatterometer and an ERS-2 C-band (5.3 cm, 5.7 GHz) SAR ( synthetic aperture radar) along with the collection of ground truth data such as volumetric and gravimetric soil water-content, surface roughness and dielectric measurements. Corner reflectors in the field were used for calibration and geo-rectification of the SAR data. The results of the microwave experiments are in a good agreement with the developed theoretical models that take into account the effects of the random surface roughness. The optical modelling of microwave processes is presented as a tool for developing the physical basis for empirical studies. This practice simplifies testing theoretical predictions and reduces the immense cost of running field and laboratory measurements in the microwave range.

Principal component analysis was used for explanation of production factors-yield relations. In this research, raster images of an organic field of wheat (Triticum furgidum var. durum), containing spatial information of several crop parameters were separated into two groups. The first group containing rasters of production factors (NO3-, soil water content (SWC), Soil Specific Area (SSA) and Carbon flux) and a second group with yield (Leaf area Index (LAI), number, of grains per kernel, and stems; weight of 1000 grains, kernel and stems). For each group it was calculated their Principal Components (PC). The first PCs of the production factors were SWC and SSA, while for the first PCs of yield were LAI, weight of stems and kernel. Since the r(2) between the PC1 of the two groups was 0.76 it was shown that SWC and SSA were the main limiting factors in the production.

The objective of this study was to develop a sensitive means of control to optimize nutrient concentrations in the root zone of a soilless system, considering plant water and nutrient uptake, and solution circulation rates. A model is proposed to simulate ornamental plants’ growth in a channel with a non-interacting soilless substrate, irrigated by point sources with constant discharge rates, spaced uniformly along the channel. The model accounts for compensation for transpiration water losses and consequent salinity buildup, and its interactions with plant growth and nutrient uptake. The added water may contain given concentrations of nutrients and/or toxic (saline) compounds, which would cause salinity buildup. Uptake of each solute is specific, according to a Michaelis–Menten kinetics mechanism, but passive uptake by the transpiration stream is also accounted for. Plant growth is affected by time/age and ionic balance in the solution. The model was calibrated with lettuce (Lactuca sativa L.) plants grown in volcanic ash. Simulation of potassium concentration change as a result of discharge rate and emitter spacing revealed that the two parameters could compensate one for the other, once a target lower limit is set. Potassium appeared to be most sensitive to sodium accumulation in the growth medium; this accumulation changed ionic concentration balance, which affected pH and bicarbonate concentration. Passive uptake of calcium by the transpiration stream is highly affected by the root fraction involved, but its calculated contribution is below published values is highly affected by the root fraction involved, but its calculated contribution is below published values.

A model is presented for water and nutrient recycle and uptake by plants grown in a soilless culture. The growth system consists of a channel, filled with a non-absorbing substrate, tilted in a given slope. The nutrient solution is applied via emitters (drippers) of given discharge rates and distances. The solution flows according to the hydraulic head gradient and conductivity, in the saturated portion of the substrate only, and drains to a reservoir at the end of the channel; transpiration losses are then compensated with water, which contains nutrients and saline substances. The solution then would be recycled to the system. Uptake is accounted for NH4-N, NO3-N, K, PO4-P, SO4-S, Ca, Mg, Na, Cl and HCO3, balanced by atmospheric CO2. The model was calibrated with data of lettuce grown in sandy soil. Simulated N uptake somewhat exceeded, but K uptake agreed with actual uptake by the plants. The model may be a useful tool to design and manage the system based on the crop potential needs for water and nutrients, and of water quality.

Production of amaryllis (Hippeastrum spp.) flowers is highly affected by the bulb size. We studied the N and K fertilization interaction with CO2 enrichment on the development of Hippeastrum bulbs grown in the greenhouse. Bulbs of two initial diameters, 3.5 and 5.4cm, were grown for 233 days in the greenhouse on dune sand, either enriched with 1000ppm CO2 or with the ambient concentration. The plants were fertilized via the drip irrigation system with combinations of NH4NO3–N (0–25mM) and K (0–6.4mM), six levels of each nutrient. Carbon dioxide was applied during daytime to an insulated section of the greenhouse. The results indicated a significant contribution to either nutrients to bulb growth, but the optimal response of the larger bulbs was at a higher CO2 concentration, for the two nutrients. The response in growth to both nutrients’ concentration was curvilinear. Enrichment with CO2 yielded an increase in bulb diameter, but the relative contribution was higher with the smaller bulbs.