Prof. Uri Shani

Ongoing Research

Modeling plant response to deficit Irrigation with saline water: separating the effects of water and salt stress in the root uptake function.

Deficit irrigation is a prefered practice where there is a need to conserve water resources or to minimize ground water contamination from deep percolation. The practice results in some degree of water stress to the crop, and possibly salt stress as salts accumulate. Ultimately, the soil must be leached to sustain crop production. Managing irrigation to maximize crop production under conditions were water use is minimized and salt accumulates in soils requires an understanding of the interactions among climate, soils, water and the plant. Mechanism-based hydrochemical models are attractive tools for designing irrigation systems, evaluating water and salt management options, and testing our understanding of the soil-water-plant-atmosphere system. The algorithms for computing water uptake and plant response to water deficit and excessive salinity have been neglected by modelers. The main objective is propose to modify the root-sink term in a mechanism-based hydrochemical model to account for matric stress via a Darcy function and osmotic stress via an exponential Maas-Hoffman response. In a parallel modeling effort, we add a salt uptake term for predicting the effects of salt accumulation on yield and water use. Lysimeter studies are used in which salinity and irrigation are varied. These studies will provide a data base for parameterizing salt uptake and salt stress functions that will also be incorporated into the model.

In-situ evaluation of unsaturated hydraulic properties using subsurface point sources.

The characterization of the hydraulic properties of the deep zone of variably-saturated and porous material is critical to predictions and modeling of transport processes between the soil surface and the groundwater. The complexity and the high costs associated with sampling in the deep vadose zone create a need for cost-effective, simple and physically-sound methods for estimation of subsurface hydraulic properties. The objectives of the current research are: i) To develop methods for obtaining rapid and reliable estimates of unsaturated hydraulic properties in-situ, based on water distribution from subsurface point sources. These can be operated with a constant flow or at a constant head. ii) To develop methods for distinguishing between matrix and preferential flow using cavities/permeameters under tension. iii) To evaluate auxiliary measurements such as soil water content or tensions near the operating cavities to improve reliability of results. iv) To develop numerical and analytical models for obtaining soil hydraulic properties based on measurements from buried-cavity sources and the auxiliary measurements.

Water application quantity and yield response to high-frequency micro-irrigation

Water application to agricultural crops, natural (rainfall) or manmade (irrigation), is characterized by its total quantity and by its allocation schedule, as determined by how this quantity is allocated throughout the growing season. It is well known that a different water quantity is needed to give the same yield when applied according to a different schedule. The underlying hypothesis is that temporal water shortage is caused when the immediate soil surrounding the root undergoes a drying process, thus resisting water flow. To overcome this temporal shortage, water flow in the root vicinity should be part of a general mass flow of water in the soil rather than a diffusion flow to the root. Low discharge or high frequency microirrigation enables a mass flow of the desired, longer duration.

The overall objective of this proposed research is to optimize micro-irrigation flow rate or pulses to maximize mass water flow in the root zone under the technological and economical constrains. The detailed objectives are: i) To relate the time length and the spatial occurrence of mass water flow in the root zone to irrigation rate or irrigation frequency under various soils, climate and crops. ii) To estimate yield water uptake relationships under the "Veihmeyer and Hendrickson concept", regular daily drip irrigation and high frequency or continuous irrigation for various climate and soils. iii) To develop a protocol for an efficient high frequency/continuous water application.

Ecological optimization of water use under irrigation in arid regions.

Irrigation is a worldwide necessity practice to achieve higher yield and needed food. Because the determination of exact water requirement, needed for each crop under specific conditions is complicated and expensive, irrigation with excess amounts of water is a common practice. This is a criminal use of a scarce resource. Moreover, the application of excessive water for irrigation results in agricultural and environmental problems. In situ measurements of deep percolation in commercial fields are practically impossible. Frequent water content measurement at various soil depths is very expensive. Furthermore, water flow may occur due to gravity even when no changes in water content can be measured. The objective of the presented proposal is to confirm the possibility of estimating water use and water percolation from yield samples, and to develop an application protocol for agricultural and natural landscape ecosystems. The specific objectives are: i)To clarify the yield-transpiration relationships in a non-agricultural, natural landscape, and in an agricultural system. ii) To establish yield-transpiration relationships during various growth stages. iii)To establish potential yield of main field crops.

This file last modified Wednesday, 04-Jun-2008 12:42:34 IDT