J. Ben-Asher

A review of rainwater harvesting

Abstract This article reviews recent literature on rainwater harvesting and its potential application for crop production. Some 170 articles published between 1970 and 1980 were found, all of them revealing an awareness of the increasing need for rainwater harvesting and a recognition of its potential. A definition of rainwater harvesting is presented on the basis of three characteristics common to it: arid to semi-arid climate, local water, and small-scale operation. The following elements are considered: runoff inducement — vegetation management, surface treatment, chemical treatment; runoff collection — Micro-Catchment Water Harvesting (MCWH) and Runoff Farming Water Harvesting (RFWH); storage and conservation. Design aspects of MCWH are reviewed: MC size, ratio of contributing area to collecting area, and layout. MCWH is especially suitable to non-irrigated areas. The Kinematic Wave Equation and Dynamic Equations have been used in modelling MCWH. RFWH can be useful in improving irrigation water availability in surface reservoirs. For modelling RFWH, the Unit Hydrograph Method is suitable. More research is required to determine the potential of runoff farming without surface reservoirs.

Micro-Catchment-Water-Harvesting (MCWH) for arid zone development

A micro-catchment consists of two elements: the runoff area A and the infiltration basin or basin area B. The water balance equations for A and B are discussed, and combined in the water balance of the micro-catchment. The water balance is used as a tool to analyze the performance of the system, and to locate problems in the water harvesting process. Water balance data were collected during the rainy season 1982/1983 from an experimental field in Sede Boqer, in the Northern Negev Desert, Israel. Eight micro-catchments of 125 m2 and four control basins of 9 m2 were used, each providing water for a single tree. Analysis of the water balance illustrates two problems: runoff production and soil water storage. Effective Micro-Catchment-Water-Harvesting (MCWH) occurs in storms with sufficient runoff to allow infiltration deep into the profile free from evaporation. Besides evaporation at the surface of the basin area, water is lost by deep percolation. Efficiencies for runoff and storage are defined, which express the relevant processes in two numbers. For the eight micro-catchments during the rainy season 1982/1983 average runoff efficiency er = 0.19, and average storage efficiency es = 0.18. The analysis shows the usefulness of the water balance approach, and the methods used to evaluate its terms. MCWH is especially suitable for application in desert fringes with about 250 mm annual rainfall and loess soils, which form a surface crust. Micro-catchments are an effective tool to scale down engineering activities. They are easy and cheap to construct, which allows active participation of the local population.

Simulation study of nutrient uptake by plants from soilless cultures as affected by salinity buildup and transpiration

Soilless plant growth systems are widely used as a means to save irrigation water and to reduce groundwater contamination. While nutrient concentrations in the growth medium are depleted due to uptake by the plants, salinity and toxic substances accumulate due to transpiration. A theoretical model is suggested, to simulate nutrient uptake by plants grown in soilless cultures with recycled solutions. The model accounts for salinity accumulation with time and plant growth, and its effects on uptake of the different nutrients by means of interaction with Na and Cl ions. The sink term occurs due to uptake by a growing root system. Influx as a function of the ion concentration is according to Michaelis–Menten active mechanisms for K+, NO3−-N, NH4+-N, PO4-P, Ca2+, Mg2+ and SO42-, whose influx parameters are affected by Na and Cl−, but not with time (age). Sodium influx is passive above a critical concentration. Sum of cations–anions concentrations is balanced by Cl− to maintain electro-neutrality of the growth solution. Salinity (by means of Na concentration) suppresses root and leaf growth, which further effect uptake and transpiration. The model accounts for instantaneous transpiration losses, during daytime only and its effect on uptake of nutrients and plant development due to salt accumulation. The model was tested against NO3− and K+ uptake by plants associated with cumulative transpiration and with different NaCl salinity levels. Deviations from observed K+ uptake should be attributed to the salinity tolerance of the plants. In a study with data obtained from published literature, the model indicated that nutrient depletion and salinity buildup might be completely different with fully grown-up plants (that do not grow) and plants that grow with time. Depletion of different nutrients are according to their initial concentration and plant uptake rate, but also affected by their interactions with Na and Cl ions.

A linear regression model combined with a soil water balance model to design micro-catchments for water harvesting in arid zones

In arid zones, where water harvesting techniques can be applied to use surface runoff for agricultural production, long-term meteorological records are often scarce. This is a problem when designing a water harvesting system, for instance, with micro-catchments. This paper presents a design method for micro-catchments, based on a simulation approach. Available rainfall and evaporation data are supplemented with soil physical data, determined from samples taken on the spot. A linear regression model combined with a transient one-dimensional finite difference water balance model is used to simulate the complete water harvesting process for a number of years. The theoretical basis of the model, including initial and boundary conditions is discussed. Experimental data from the Northern Negev Desert are used to calibrate the model. The water balance is simulated for two sets of soil physical properties, and for extremely arid and arid conditions. The performance of micro-catchments with varying runoff area A and basin area B is studied. This AB ratio is a key parameter in micro-catchment design. The following conclusions are drawn: (1) extremely arid conditions (‘true desert’) are too dry for micro-catchment-water-harvesting; (2) for arid conditions with average annual rainfall of ca. 200 mm, and the trees and loess soil considered, a preliminary design would have a basin area B of ca. 40 m2 and a runoff area A of between 40 and 80 m2.

Canopy temperature to assess daily evapotranspiration and management of high frequency drip irrigation systems

Abstract The infrared thermometer (IRT) can be an important tool for detection of crop water stress symptoms for it measures the canopy temperature. This enables the system operator to translate it into a crop water stress index (CWSI). IRT has not yet been used to manage irrigation by using it to estimate the daily transpiration rate. The goal of this study was to test the applicability of IRT to control precise irrigation by: (1) comparing crop water stress index (CWSI) with standard pressure chamber, and (2) comparing IRT-estimated transpiration of tomato and cotton with other, more standard, methods. A model for using IRT as a tool for evaluating daily transpiration is presented. This was tested in Israel and California. The IRT was found to measure adequately differences in canopy temperature and its derivatives only when water treatments differ largely from one another. Good agreement was obtained under optimal water regime when daily lysimeter measurements were compared to IRT measured transpirations. An acceptable correlation was obtained when CWSI was related to ψ L (leaf water potential). The resolution of IRT was insufficient to detect small differences between well irrigated treatments; nor was it able to assess transpiration on a short-time scale. It is concluded that at its present status implementation of the IRT using both CWSI and transpiration estimation could not improve efficiency of high frequency irrigation.

A model for nutrient and water flow and their uptake by plants grown in a soilless culture

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 daily runoff simulation in semi-arid watersheds based on soil water deficit calculations

Initial soil water content just before a rainfall event is an input required for the calculation of a basins water balance including infiltration and runoff. However, for most watersheds such information is not available because its evaluation involves a large amount of labor. The objective of this study is to describe a practical model with which to estimate time-dependent changes of a basins soil water content. It is further used for predicting runoff water yield when rainfall depth is the only known component of the water balance equation (WBE). Two distinct cases of the WBE are discussed: (1) a runoff-producing storm; (2) a storm without runoff. Runoff events from four watersheds in southern Arizona were measured throughout 8 to 17 years and analyzed in this study. Rainfall-runoff relationships are described in this model by an empirical quadratic regression equation which includes four parameters. They were estimated by an optimization subroutine which was used to determine the minimum difference between measured and modeled results. The optimized parameters enable simulations of the continuous dynamic change of an index of the soil water content as well as predictions of runoff depths. It was found that the predicted runoff agrees reasonably well with the observed runoff. The minimum coefficient of determination (r2) between the computed and actual runoff for the multi-annual data sets was 0.62 and the maximum 0.86. Runoff threshold value was found to be a function of the basin average soil texture. The lowest threshold was 4.6 mm for clay soil and the largest was 9.0 mm for sandy soil. Since direct soil water measurements were not taken, we interpreted the acceptable agreement between measured and predicted runoff as an indirect validation of the soil water model. It is concluded that the model could be useful for extending short records of simulated runoff on nearby ungaged watersheds in semi-arid regions.

Root aeration in a deep hydroponic system and its effect on growth and yield of tomato

Abstract Tomato plants ( Solanum lycopersicum L. ‘Grandia’) were grown in a deep-water culture system, with varying oxygen (O 2 ) concentrations in the nutrient solution. Oxygen depletion of the nutrient solution by the plants as a function of distance from an aeration point could be best described by a concave exponential curve. Increase of branch length, number of side branches and number of flowers per plant were plotted against time and found to produce different types of curves (exponential, logarithmic and linear, respectively). The slopes of the best-fit functions of these curves were linearly correlated to the O 2 concentration in the hydroponic medium. The effect of O 2 concentration in the nutrient solution on the fresh and dry weights of roots and shoots was positive and exponential. There were no significant changes in response to O 2 in the ratios of root to shoot fresh and dry weights, or of the ratios of dry to fresh weights of roots or shoots. Fruit production increased linearly with O 2 concentration around the roots. It was concluded that tomato plants in deep-water culture do not reach the theoretical maximum rate of O 2 uptake into the roots.

The effect of salinity on parameters of potassium and nitrate uptake of cotton

Abstract Salt damage to plants may be caused by competition in uptake between salt ions and nutritional ions. The effect of sodium chloride (NaCl) on nitrate (NO3), o‐phosphate (P), and potassium (K) uptake by cotton (Gossypium hirsutum L.) was measured. Plants were grown in nutrient cultures with added 0–450 mM NaCl for 41 days. Uptake of NO3, P, and K was measured according to their depletion in the solution with time, and measured root surface area. Net‐influx In in low external concentrations was assumed to obey the Hill equation: In =Imax.Cn/(Ka n+Cn), where C is concentration, Imax the value of In when C is infinite, Ka is the apparent Michaelis‐Menten coefficient, and n is the cooperativity index. The results showed a depression in Imax of K with increasing NaCl in the solution, accompanied by an increase in Ka and n. Nitrate Imax and n were not affected, but its Ka somewhat increased with NaCl concentration. All the three parameters for phosphate influx slightly increased in higher NaCl concentrat...

Root distribution under trickle irrigation: Factors affecting distribution and comparison among methods of determination

Abstract Four methods were used to characterize root distribution under drip (trickle) irrigation:root weight, cation exchange capacity (CEC), uptake of 86Rb, and the line intersect method. Trickle irrigated tomato (Lycopersicon esculentum Mill. var. Naama) and peanut (Arachis hvpogeae L. var. shulamit) plants were grown on sandy soil (Typic Torripsamment) and their roots were used for the study. The four methods showed that most of the roots are concentrated close to the emitter. A linear correlation was found between root weight and the uptake of 86Rb. This indicated that although roots near the emitter seem to be relatively old, the uptake activity is also concentrated there. Furthermore, it is apparent that the effect of the limited root distribution is even more pronounced when using CEC as an indicator for fine roots or surface area, than when using weight as an indicator. It was therefore concluded that all criteria emphasized the restricted distribution of roots as well as their activity in the we...