Alon Ben-Gal

Combined effect of salinity and excess boron on plant growth and yield

Plants are likely to be affected by simultaneous salinity and boron (B) toxicity stresses due to exposure to soils with high levels of naturally occurring salinity and B, or due to irrigation with water containing high levels of salts, including B. Inadequate information regarding the response of plants to the combination of excess B and salinity on plant growth and yield is available, and there is no consensus concerning mutual relations between salinity stress and B toxicity. Growth and yield of bell pepper (Capsicum annuum L.) were measured at different B and salinity levels in two greenhouse experiments. The results from these experiments and from published data for wheat, tomato and chickpea were analyzed according to the Abbott method to define the combined effect of B and salinity on plant growth and yield. Application of the Abbott method for the experiments on peppers generally implied an antagonistic relationship for excess B and salinity. In other words, toxic effects on growth and yield were less severe for combined B toxicity and salinity than what would be expected if effects of the individual factors were additive. Similar antagonistic characteristics were found using data from three of the five studies reported in the literature. The mechanism of relationships between B and salinity in plants is not clear and several options are discussed. Prominent among the possible explanations are reduced uptake of B in the presence of Cl and reduced uptake of Cl in the presence of B.

Evaluating water stress in irrigated olives: correlation of soil water status, tree water status, and thermal imagery

Irrigation of olive orchards is challenged to optimize both yields and oil quality. Best management practices for olive irrigation will likely depend on the ability to maintain mild to moderate levels of water stress during at least some parts of the growing season. We examined a number of soil, plant and remote sensing parameters for evaluating water stress in bearing olive (var. Barnea) trees in Israel. The trees were irrigated with five water application treatments (30, 50, 75, 100 and 125% of potential evapotranspiration) and the measurements of soil water content and potential, mid-day stem water potential, and stomatal resistance were taken. Remote thermal images of individual trees were used to alternatively measure average canopy temperature and to calculate the tree’s crop water stress index (CWSI), testing empirical and analytical approaches. A strong non-linear response showing similar trends and behavior was evident in soil and plant water status measurements as well as in the CWSI, with decreasing rates of change at the higher irrigation application levels. No statistically significant difference was found between the analytical and the empirical CWSI, suggesting that the relative simplicity of the analytical method would make it preferable in practical applications.

Subsurface Drip Irrigation in Gravel-Filled Cavities

Subsurface drip irrigation (SDI) is regularly used to provide water and nutrients to plants while maintaining a dry soil surface. Problems associated with the practice of SDI are spatially dependent reductions in dripper discharge and possible surfacing of water resulting from positive pressure at the emitter–soil interface. These can be resolved either through prudent care in matching dripper flow rates to soil hydraulic properties or by otherwise providing conditions under which positive pressure cannot arise. We present a method where water is applied to the soil within a gravel-filled cavity. The necessary volume of gravel is determined by the contact area between the cavity and the soil and is a function of irrigation rates, dripper spacing, and soil hydraulic properties. A theoretical solution for the radius of a gravel-filled cavity based on the perimeter of the saturated zone from a line source in the soil demonstrates that larger cavities are needed as soil hydraulic conductivity decreases. The method was tested using a numeric simulation model (HYDRUS-2D) and was used and tested in a vineyard of table grapes ( Vitis Vinifera L. cv. Sugraone) in a 7-yr study with SDI and gravel-trenched subsurface application of effluent and fertilizers.

Fertilization and blending alternatives for irrigation with desalinated water.

In arid-zone agriculture where available irrigation water is saline, desalination is becoming an attractive method for increasing yields and reducing negative environmental consequences. However, irrigation with desalinated water can be problematic if essential nutrients, including Ca, Mg, and S, removed during reverse osmosis, are not reintroduced. We evaluated two strategies for supplying these nutrients - direct fertilization and blending of desalinated with saline groundwater -experimentally in a greenhouse and in a model for a case study regarding pepper (Capsicum annuum L.) production. Reducing salinity from electrical conductivity (EC) 3.20 to EC 0.40 dS m(-1) by reverse-osmosis desalination increased maximum yields by almost 50% while allowing a reduction of applied irrigation water to half of that with the saline water, but the associated cost of fertilizing with Ca, Mg, and S minerals was high (around

The influence of bearing cycles on olive oil production response to irrigation

0.50 m(-3)). Blending 30% saline water with 70% desalinated water brought Ca, Mg, and S minerals to satisfactory levels while producing water with salinity of EC = 1.35 dS m(-1). Comparison of relative pepper yields and analysis of simulated results showed that irrigation with blended water maintained yields greater than 90% compared to irrigation with fully desalinated water, but only as irrigation rates were increased by more than 50%. The environmental cost of the increase in irrigation-water salinity from EC 0.40 to EC 1.35 dS m(-1) in the blended water was shown to be substantial as it involved five times greater loading (into the soil) and leaching (beyond the root zone) of salts and other contaminants.

Sweet corn response to combined nitrogen and salinity environmental stresses

Water requirements for olive oil production and the effects of deficit irrigation were determined while considering the relative fruit loads on trees occurring as a result of biennial bearing cycles. Two Israeli olive (Olea europaea) varieties (Barnea and Souri) were evaluated for growth and yield parameters in a 4-year field study where five relative irrigation rates were applied. Increasing irrigation increased stem water potential, vegetative growth, and olive fruit yield with the increases tapering off at application rates reaching 75–100% of potential crop evapotranspiration. Tree water status, growth, and fruit characteristic parameters were highly affected by both fruit load and by irrigation level. Oil yield increases as a function of increased irrigation were initiated for each cultivar only following an ‘off’ season when the treatments lead to higher vegetative growth. The increased oil yields as a function of increased irrigation were primarily explained by higher tree-scale capacity for carrying fruit, especially as irrigation alleviated measureable water stress. For the Barnea cultivar in ‘on’ years, a secondary effect due to increased oil per fruit as irrigation increased was evident, particularly at the higher application rates.

Drainage water reuse: biological, physical, and technological considerations for system management.

To define the nature of the combined response curve of sweet corn (Zea mays L.) plants to nitrogen and salinity, a lysimeter study was designed to follow water and solute budgets with combinations of the two variables over wide ranges of 0.5–7.5 dS m−1 and 0–150% of local N-fertilization recommendations. Patterns of water-use efficiency, N content, N uptake, and shoot dry-matter yield indicated the predominance of environmental interactions over Cl-nitrate physiological antagonism. At low salinities, the leaf N content, N uptake, and yield increased with increased N fertilization up to 45% of local N-fertilization recommendations, nitrogen was efficiently stripped from the percolating water and practically no nitrate was leached. At higher N fertilization the amount of leached N increased linearly with increased N input, and N uptake and yield were independent of N rates, levelling off at increased values for decreased salinities. The Liebig–Sprengel and Mitscherlich–Baule models were evaluated against measured data; both achieved similar values for the systems inherent N, the salinity level corresponding with zero-yield, and the predicted yields, which were highly correlated with the experimental data (R2 > 0.9). It is suggested that both models can be used successfully in mechanistic-based plant–soil solution models to predict yield, water and nutrient needs, and the resulted N leaching.

Temporal robustness of linear relationships between production and transpiration

Previous reviews of drainage water reuse have discussed principles of water reuse and disposal; provided examples of reuse practices; offered reuse criteria for salinity, for trace elements, and for bacteria; discussed mitigation of dissolved trace elements in reuse strategies; and summarized the California experience with a focus on discussion of salinity, sodicity, B, Mo, and Se issues. This review emphasizes recent literature contributing to understanding physical and biological constraints to drainage water reuse. The potential for drip irrigation and, particularly, low-flow/high-frequency systems to enhance the use of drainage water while minimizing the deleterious effects on yield and on water and soil resources is examined using the numeric HYRDUS-2d model. Additionally, an analytical model is used to illustrate physical and biological limitations to drainage water management that result from the self-regulating nature of the soil-plant-water system. The models suggest that crop, soil, irrigation frequency, and delivery systems might be manipulated to reduce the quantity of drainage water, but they also suggest that the nature of the system may seriously constrain the amount of reduction that might be achieved.

Nursery and post-transplant field response of olive trees to arbuscular mycorrhizal fungi in an arid region

Seasonal dependence of biomass production on transpiration has been previously reported for a number of crops under salinity and drought. Linear yield (Y) to transpiration (T) relationships have been utilized in plant-growth and water-uptake models to estimate yield based on predicted transpiration values. The relationship is often employed for time steps that are very small compared with the whole season measurements, even though no empirical validation exists for such application. This work tests the hypothesis that linear Y-T relationships are valid throughout the life span of crops under varied natural conditions and levels of environmental stress. Effects of salinity and water supply on growth, water use and yields of tomatoes (Lycopersicon esculentum Mill.) were studied for two distinct conditions of potential transpiration. Linear relationships between relative Y and relative ET were found to be consistent throughout the life span of the crops for both growing seasons. Water-use efficiency increased together with plant growth as a result of changes in the plants surface area to volume ratio. This empirical validation of linear Y-T relationships for short time periods is beneficial in confirming their usefulness in growth and water uptake models.

Spatial and diurnal below canopy evaporation in a desert vineyard: Measurements and modeling

We evaluated arbuscular mycorrhizal fungi (AMF) for enhancement of irrigated olive (Olea europaea L.) tree growth and vigour under arid horticultural conditions. The response of 12 common commercial olive cultivars to AMF (Glomus mosseae and Glomus intraradices) inoculation was measured in a nursery experiment. Long-term post- transplanting response to AMF inoculation (G. intraradices alone or G. intraradices+G. mosseae) at the seedling stage was also assessed for 3 cultivars in an irrigated orchard in an arid region. Two control treatments without AMF inoculation were evaluated: one with fertilisers provided as in commercial olive nurseries, the other with no fertiliser application during the time of the inoculation treatments. Inoculated v. uninoculated plants in the nursery showed increases in height, and root andshootbiomass.Intensityofresponsewashighlycultivar-specific.OlivetreesinoculatedwithAMFalsoperformedbetter than untreated plants in the orchard experiment. Inoculated plants in the nursery showed consistent increases in P and K contentbothinleavesandroots.Fertilisationatthe firstgrowthstage,afterrooting,didnotcontributetoseedlinggrowthand therefore,thepracticeofstoppingfertilisationtopromoteAMFinoculationwasfoundacceptable.Withthecorrectchoiceof cultivar-inoculumcombination,AMFinoculationtechnologycanbenefitolivecultivation,particularlyinaridregionswhere native AMF levels are low.