Impact of a gel conditioner and water quality upon soil infiltration

Summary The interactive effects of 0.0%, 0.4%, and 0.8% of a gel conditioner, Jalma, and four waters: salt solution (SS), distilled (DW), natural sewage (SW), and well (WW) waters on swelling (S), effective mean pore radius ( ), water penetrability (), diffusivity (D), and weighted-mean diffusivity ( ) in loamy sand and loam soil columns were investigated. The diffusivities of water in untreated soil columns were nearly independent of water quality. In general for both soils, S decreased, and , , and increased with increase in water salinity and decrease in % Jalma. For the loamy sand of SS, WW, SW, and DW were reduced, respectively by 15%, 39%, 45%, and 55% due to the addition of 0.4% Jalma and by 15%, 52%, 69%, and 83% due to addition of 0.8% Jalma compared to untreated control. It was concluded that 0.4% Jalma is the optimum rate when sewage (EC=1.6 dSm^–1) or other waters of low salinity are used for irrigation and 0.8% Jalma when well water (EC =6.4 dSm^–1) is used. When the irrigation water is of high salinity (EC =42.5 dSm^–1), use of this gel conditioner is not recommended. Effective mean pore radius proved to be a reliable predictor of the multiple effects of texture, Jalma and water salinity on and .     

The effect of high sodium irrigation water on soil salinity and yield of mature grapefruit orchard

Summary Citrus is considered to be specifically sensitive to chloride and sodium, yet little data exist to show the effect of these ions on yield. An experiment was started in 1978 to study the effect of sodic irrigation water on yield. The treatments were SAR of the irrigation water of 2.8-(L), 5.5-(M), and 10.3-(H) (mol/m³)^1/2 . The experiment follows a study on the same plots using irrigation water of variable chloride concentration and a uniform SAR of 4.2 (mol/m³)^1/2.The high SAR, high Cl water resulted in a yield reduction of 9% from the control treatment. This reduction was similar to the reduction observed when only Cl was a variable. Total water uptake was reduced as salt concentration in the soil increased. The average water uptake for the four irrigation seasons 1978 to 1981 was 1025 mm, 953 mm and 823 mm for the L, M and H treatments, respectively.Soil ESP was increased as a result of sodium accumulation in the soil profile in the M and H treatments, while Cl and EC remained relatively constant with time during the experiment. After four years of irrigation the infiltration capacity values were 0.26, 0.17 and 0.16 cm/h for the L, M and H treatments, respectively. Fruit quality was not affected by the treatments.No specific toxicity symptoms were observed when the Na concentration in the soil saturation extract was 16 mol/m³ and the ESP was 8.0. The results lead to the conclusion that within the range used in this experiment the high ESP did not specifically effect yield and that yield response was due to the total salt concentration in the soil.Contribution from the Agricultural Research Organization, The Volcani Center, Bet Dagan, Israel, No. 626-E, 1982 series     

Salt tolerance of irrigated guayule

Summary The salt tolerance of guayule (Parthenium argentatum Gray cv. N565-II) was tested in small held plots (silty clay soil) in the Imperial Valley of California. Seedlings were transplanted in October 1981. Differential salination was begun in March 1982 and continued for 4 years by irrigating with waters salinized with NaCl and CaCl₂ (1:1 by wt.) to obtain electrical conductivities of 0.8, 1.4, 3, 6, 9, and 12 dS/m. Dry matter, rubber, and resin yields were determined from pollarded plants in February 1984 and uprooted plants in February 1985 and 1986. Rubber concentrations in the woody branches in 1984 and 1985 averaged 6.1 and 7.3%, respectively on a dry weight basis and were not significantly affected by soil salinity. Resin concentrations averaged 8.6% and 7.3% for the two years. In 1986, both rubber and resin concentrations decreased with increased salinity. Rubber and resin concentrations in the root crowns were approximately one percentage point less than those of the shoot. Dry matter and resin yields were not affected by salinity until the time- and depth-averaged electrical conductivity of the saturated-soil extracts ( ) taken from the rootzone (0–90 cm) exceeded 8.7 dS/m. Above 8.7 dS/m, both yields decreased 11.6% per dS/m increase in . Rubber yields decreased 10.8% per dS/m above a threshold of 7.8 dS/m. Plant mortality rather than growth reduction at high levels of salinity appears to be the limiting factor for rubber production from irrigated guayule.     

Tomato root distribution, yield and fruit quality under different subsurface drip irrigation regimes and depths

Tomato rooting patterns, yield and fruit quality were evaluated in a field trial where three irrigation regimes [0.6 (DI), 0.9 (DII) and 1.2 ET_c (DIII)] and three drip irrigation depths [surface (R0), subsurface at 20 cm depth (RI) and subsurface at 40 cm depth (RII)] were imposed following a split-plot experimental design, with four replications. The behaviour of the root system in response to the irrigation treatments was evaluated using minirhizotrons installed between two plants, near the plant row. Root-length intensity (L _a)—length of the root per unit of minirhizotron surface area (cm cm⁻²)—was measured at four crop stages. For all sampling dates, none of the factors studied were found to influence L _a or rooting depth significantly or the interaction between treatments. For all treatments most of the root system was concentrated in the top 40 cm of the soil profile, where the root-length density ranged from 0.5 cm cm⁻³ to 1.4 cm cm⁻³ . The response of tomato fruits to an increase in the water applied was similar in quantitative and qualitative terms for the different drip irrigation depths. Water applied by drip irrigation had the opposite effect on commercial yield (t ha⁻¹) and soluble solids (°Brix) (r=−0.82, P<0.001), however, yield in terms of total soluble solids (t ha⁻¹) was the same for the 0.9 and 1.2 ET_c. The increase in commercial yield can be described by the equation      

Rubber production of salt-stressed guayule at various plant populations

Summary The hypothesis that increasing the plant population of guayule (Parthenium argentatum) to compensate for the reduced plant canopy size caused by soil salinity coupled with an anticipated enchancement of rubber production under the moderate environmental stress imposed by salinity was tested in a field plot experiment in the Imperial Valley of California. Irrigation waters having electrical conductivities (EG _i ) of 1.2, 3.2, 6.5, and 9.4 dS/m were applied for 4 years to plots having plant populations of 28,000, 56,000, and 84,000 plants per hectare. The influence of salinity on rubber and resin production was independent of plant population. The salt tolerance threshold, maximum average salinity level of the root zone measured as the electrical conductivity of saturated soil extracts ( ) without yield reduction, was 7.5 dS/m; beyond this threshold, rubber production was reduced 6.1% per unit increase of soil salinity. The salinity values were averaged through the root zone from planting to harvest. The average rubber content — 7.9% — was altered little by treatment or harvest age for 2- to 4-year-old plants. Resin content averaged 8.4% but increased salinity and increased plant population increased the resin content slightly in some cases. Dry matter production of shoots for the nonsaline treatment was 259 kg/ha/month for pollarded (clipped) shoots after 31 months, 203 kg/ha/month for shoots harvested after 43 months, and 401 kg/ha/month for the 24-month period after pollarding. Combining the shoot mass after 31 and 55 months gave an average growth rate of 321 kg/ha, supporting the recommendation for pollarding. Monthly growth rates for the lowest salt treatment (3.2 dS/m) were about 10% less than for the nonsaline treatment (1.2 dS/m). The hypothesis tested was proven to be false because neither increased salinity nor increased plant population increased rubber production.     

Assessing water stress in a hedgerow olive orchard from sap flow and trunk diameter measurements

We used sap flow and trunk diameter measurements for assessing water stress in a high-density ‘Arbequina’ olive orchard with control trees irrigated to replace 100 % of the crop water needs, and 60RDI and 30RDI trees, in which irrigation replaced ca. 60 and 30 % of the control, respectively. We calculated the daily difference for both tree water consumption ( $ D_{{E_{\text{p}} }} $ ) and maximum trunk diameter (D _MXTD) between RDI trees and control trees. The seasonal dynamics of $ D_{{E_{\text{p}} }} $ agreed reasonably well with that of the stem water potential. We identified peculiarities on the response $ D_{{E_{\text{p}} }} $ to changes in water stressing conditions, which must be taken into account when using the index. An analysis of the water stress variability in the orchard is required for choosing the instrumented trees. The reliability of the D _MXTD index was poorer than that of $ D_{{E_{\text{p}} }} $ . The maximum daily shrinkage (MDS) was not a reliable water stress indicator.     

Continuous measurement of plant and soil water status for irrigation scheduling in plum

The usefulness of continuous measurement of soil and plant water status for automated irrigation scheduling was studied in a drip-irrigation experiment on plum (Prunus salicina Black Gold). Two levels of water restriction were imposed at different phenological periods (from pit-hardening to harvest, post-harvest) and compared with a well irrigated control treatment. Soil matrix water potential (_soil) was measured with granular matrix sensors (Watermark); and short-period trunk diameter variation (TDV) was measured with linear variable displacement transformers. The Watermark sensor readings were in reasonable agreement with the irrigation regime and showed a good indication of plant water status across the season (r²=0.62), although they were a better predictor of stem water potential (_stem) in the dry range of _soil. Nonetheless, the most important drawback in their use was the high variability of readings (typical CV of 35–50%). From TDV measurements, maximum daily shrinkage (MDS) and trunk growth rate (TGR) were calculated. Their performance was also compared with _stem, which had the lowest variability (CV of 7%). During most of the fruit growth period, when TGR was minimum, MDS was higher in the less-irrigated treatment than in the control and correlated well (r²=0.89) with _stem. However, after harvest, when TGR was higher, this correlation decreased as the season progressed (r²=0.73–0.52), as did the slope between MDS and _stem, suggesting tissue elasticity changes. Later in the season, TGR was better related to plant water status. These observations indicate some of the difficulties in obtaining reference values useful for irrigation scheduling based exclusively on plant water status measurements.     

Impact of research on water use for irrigation in Israel

The decrease of annual irrigation application rate observed since 1950 was reversed in 1988 as a result of a sudden increase of the amount of treated effluents used for irrigation. Intensification of research on irrigation with effluents and marginal water starting in 1994 resulted four years later in the renewal of the decrease of irrigation application rate. Contribution No. 614/06 from the Agricultural Research Organization, The Volcani Center, Bet Dagan, Israel.

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Effects of salinity on germination,seedling growth,and yield of melons

Summary Four melon (Cucumis melo L.) cultivars were tested for salt tolerance at germination, seedling growth stages, and plant maturation. Noy Amid was the most tolerant during germination, achieving 56% germination in 15,000 mg/l NaCl solution. However, this cultivar and Eshkolit Ha 'Amaqim were relatively sensitive during the first 4 days' growth of the radicle and the hypocotyl, and the first 3 weeks' development of the seedling. Their yields were reduced under saline as compared with non-saline field conditions. In contrast, Honey Dew and Rochet had little or no germination in 15,000 mg/l NaCl but showed salt tolerance during seedling growth stages. Yield of Honey Dew was unaffected by saline field conditions, and that of Rochet was not significantly reduced from the non-saline control. Thus, selection for salt tolerance in melons appears feasible during early vegetative growth stages but not during germination.Contribution No. 1032-E, 1984 series, from the Agricultural Research Organization, Bet Dagan, Israel     

Water-conserving wheat irrigation schedules based on climatic records

Summary Correlations between spring rainfall and grain yield were determined for four winter wheat cultivars (Triticum aestivum L. em. Thell. Triumph, Wichita, Concho, and Triumph 64), grown between 1950 and 1977 under dryland conditions at Stillwater, in the East Central region of Oklahoma, and at Goodwell, located in the drier, western part of the state.At Stillwater, all but one of the cultivars exhibited maximum positive correlations between rainfall and yield in the fourth week of March, when stem-extension occurs. Smaller positive correlations were observed in mid-April when flowering. Results at Goodwell were similar except that the correlations between rainfall and yield were lower and occurred earlier than at Stillwater and showed a less marked secondary peak at flowering. These results agree with those of experiments in which irrigation has been applied at different growth stages of wheat, and have shown that both stem-extension and flowering are critical stages of water requirement. As the results of this climatic study show that the peak correlations between rainfall and yield occur at these same two stages, it is suggested that long-term climatic data could be used to determine optimum timing for irrigation of wheat.Such an approach should save water and energy by limiting irrigation to those times when analysis of local records demonstrates the maximum positive correlation between rainfall and yield.     

Irrigation scheduling in a mature peach orchard using tensiometers and dendrometers

Three trickle irrigation schedules, two of which were scheduled according to soil water potential ( soil) (tensiometer method) and daily stem contraction (DSC) (dendrometer method) respectively and the other one was a schedule of restricted water supply, were applied to a mature peach orchard.The annual water application based on soil was greater than that based on DSC. However, tree growth, fruit size and leaf water potential (leaf) on the trees in the dendrometer scheduling plot did not differ from those in the tensiometer scheduling plot while the premature fruit drop and fruit bud initiation were greatly different. The restricted water supply treatment limited significantly both tree and fruit growth. In addition, the lower leaf was observed on the trees in this plot.Further study shows that use of the dendrometer method for scheduling irrigation satisfies the water needs of the plant and that the tensiometer method is less accurate.Abbreviations leaf leaf water potential - soil soil water potential - DSC daily stem contraction - LVDT linear variable displacement transducer - PET potential evapotranspiration     

Effect of soil water osmotic potential on growth and water relationships in barley during soil water depletion

Summary Barley plants (Hordeum distichum, L., cv. Zita) grown in a sandy soil in pots were adjusted during a pretreatment period of 5 days to three levels of soil water osmotic potential by percolating 61 of a nutrient solution with additional 0, 22.3 and 44.6 mM KCl. A drying cycle was then started and the plants were harvested when the soil water matric potential had decreased to –1.4 MPa, respectively 6, 7 and 8 days later.No significant differences in dry matter yields, transpiration coefficients and wilting percentages were found between treatments.During the drying cycle leaf water potential ( _l ) decreased concomitantly with decrease in soil water potential ( _s ) with almost constant and similar differences ( _l – _s ) for all treatments despite differences in levels of potentials. The concomitant decrease in leaf osmotic potential () was due partly to dehydration (58%) and partly to increase in leaf solute content (42%) independent of treatment. The part of total osmotic solutes due to K decreased relatively during the drying cycle.Close relationships were found between and _l as functions of relative water content (RWC). Identical curves for the two levels of salt treatment agree with similar concentrations of K, Cl, and ash found for salt treated plants indicating that maximum uptake of macro nutrients may have been reached.During the main part of the drying cycle the turgor potential as function of RWC was higher and decreased less steeply with decreasing RWC in the salt treated than in the non-salt treated plants.In the beginning of the drying cycle additions of KCI lowered the transpiration rates of the salt treated plants resulting in a slower desiccation of the soil and hence an increased growth period. A delay in uptake from a limited soil water supply may be advantageous during intermittent periods of drought.     

Infiltration and runoff as affected by pitting,mulching and sprinkler irrigation

Summary Changes in infiltration and runoff caused by pitting and mulching under sprinkler irrigation were studied on two soil types. Pitting or diking was done with an implement called a dammer-diker. Five soil treatments were applied: shallow and deep dammer-diker, shallow dammer-diker with mulch, bare, and a mulched soil, combined with two water application rates. Total water infiltration and runoff varied during the experiment. Runoff decreased with area of water storage provided by the pits and the less water was applied. Mulch treatments also reduced runoff. Surface water storage decreased during the season. Changes in soil physical properties due to pitting were more important in controlling runoff than surface water storage.The effective saturated hydraulic conductivity of the soil progressively decreased through the season for all soil treatments and water application rates.A model was developed to simulate the effect of pits on runoff. On a silt loam soil, simulated percent runoff and accumulated runoff over time for the bare and pitted treatments agreed closely to measured values. The agreement of simulated to measured runoff for a silty clay loam soil was not as good probably because of cracking which the simulation model did not take into account.     

Daily evapotranspiration estimates from extrapolating instantaneous airborne remote sensing ET values

In this study, six extrapolation methods have been compared for their ability to estimate daily crop evapotranspiration (ET_d) from instantaneous latent heat flux estimates derived from digital airborne multispectral remote sensing imagery. Data used in this study were collected during an experiment on corn and soybean fields, covering an area of approximately 12 × 22 km, near Ames, Iowa. ET_d estimation errors for all six methods and both crops varied from −5.7 ± 4.8% (MBE ± RMSE) to 26.0 ± 15.8%. Extrapolated ET_d values based on the evaporative fraction (EF) method better compared to eddy covariance measured ET values. This method reported an average corn ET_d estimate error of −0.3 mm day⁻¹, with a corresponding error standard deviation of 0.2 mm day⁻¹, i.e., about 5.7 ± 4.8% average under prediction when compared to average ET_d values derived from eddy covariance energy balance systems. A solar radiation-based ET extrapolation method performed relatively well with ET_d estimation error of 2.2 ± 10.1% for both crops. An alfalfa reference ET-based extrapolation fraction method (ET_rF) yielded an overall ET_d overestimation of about 4.0 ± 10.0% for both crops. It is recommended that the average daily soil heat flux not be neglected in the calculation of ET_d when utilizing method EF. These results validate the use of the airborne multispectral RS-based ET methodology for the estimation of instantaneous ET and its extrapolation to ET_d. In addition, all methods need to be further tested under a variety of vegetation surface homogeneity, crop growth stage, environmental and climatological conditions.

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An improved Lewis-Milne equation for the advance phase of border irrigation

Summary The Lewis-Milne (LM) equation has been widely applied for design of border irrigation systems. This equation is based on the concept of mass conservation while the momentum balance is replaced by the assumption of a constant surface water depth. Although this constant water depth depends on the inflow rate, slope and roughness of the infiltrating surface, no explicit relation has been derived for its estimation. Assuming negligible border slope, the present study theoretically treats the constant depth in the LM equation by utilizing the simple dam-break wave solution along with boundary layer theory. The wave front is analyzed separately from the rest of the advancing water by considering both friction and infiltration effects on the momentum balance. The resulting equations in their general form are too complicated for closed-form solutions. Solutions are therefore given for specialized cases and the mean depth of flow is presented as a function of the initial water depth at the inlet, the surface roughness and the rate of infiltration. The solution is calibrated and tested using experimental data.Abbreviations a (t) advance length - c mean depth in LM equation - c _f friction factor - c _h Chezy's friction coefficient - g acceleration due to gravity - h(x, t) water depth - h ₀ water depth at the upstream end - i() rate of infiltration - f(x, t) discharge - q₀ constant inflow discharge - S _f energy loss gradient or frictional slope - S₀ bed slope - t time - u(x, t) mean velocity along the water depth - x distance - Y() cumulative infiltration - (t) distance separating two flow regions - infiltration opportunity time     

Water tension thresholds for processing tomatoes under drip irrigation in Central Brazil

Drip irrigation has the potential to save water and mitigate foliar diseases for processing tomato production in Central Brazil. Four experiments were carried out at Embrapa Vegetables, Brasília, Brazil, to establish irrigation management strategies during vegetative, fruit development, and maturation growth stages of drip-irrigated processing tomato. Soil water tension (SWT) threshold values ranging from 5 to 120 kPa were evaluated. Plants growing under higher water deficit during the vegetative stage showed root systems up to 10 cm deeper than those irrigated more frequently. Maximum fruit yield was reached when irrigations were performed at SWT thresholds of 35, 12, and 15 kPa during vegetative, fruit development, and maturation growth stages, respectively. Total soluble solids content was not affected by irrigation treatments during vegetative and fruit development stages, but increased as SWT increased during fruit maturation growth stage.

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The reorganization of water users' associations in Mendoza,Argentina

This paper describes the changes introduced in water users' associations in the Province of Mendoza, Argentina. Before 1985 there were 709 water users' associations, known as Canal Inspection, each of them in charge of the administration of an area of about 300 ha, corresponding to tertiary and quaternary canals. At present there are 21 reorganized inspections administering an average area of 6 000 ha. The democratic system for the election of authorities is described and the method of budget preparation and control is discussed. The advantage of reorganization is illustrated through the economic assessment of the Reduccion Main Canal. This canal irrigates an area of 13 985 ha. The annual benefits due to reorganization are estimated to total A 32 800 (US$ 41 000), being 2.1 times the annual budget of the Inspection.     

Quick Estimation of Hydraulic Conductivity in Unsaturated Sandy Loam Soil

Laboratory experiments were conductedfor determining hydraulic conductivity duringinfiltration in an unsaturated sandy loam soil, usingboth steady state and equilibrium methods. A constanthead Guelph permeameter and a volumetric pressureplate extractor were used. Based on two ponded heightsin the permeameter, the parameters of Gardner'sequation expressing the unsaturated hydraulicconductivity as a function of pressure head (i.e. thesaturated hydraulic conductivity K_s and theexponent ), were estimated simultaneously.Furthermore, it was found that the parameter ,could also be predicted from the soil-water retentioncurve based on equilibrium data obtained from theextractor. This indicated that, for the soil typestudied, one-ponded height in the permeameter methodcould be sufficient for the determination of theexponent , provided that the soil-water retentioncurve is known.     

Verification of impermeable barrier depth and effective radius for drain spacing using exact solution of the steady state flow to drains

The steady-state drainage equation ofHooghoudt (1940) has adrawback that tables for the determination of the so-calledequivalentlayer, d_e are needed. These calculations arecumbersome as d_e is dependenton the unknown spacing. Moreover, additional head islost due to theconvergence of stream lines towards the finite numberof perforations withinthe pipe wall. Therefore, corrections are required byreplacing the actualdrain radius by its effective radius. The designers inEgypt assume that thedepth of impermeable layer is infinity which resultsin an over estimationof drain spacing that will affect the ability of thedrainage system.Van der Molen and Wesseling (1991) have developed aseries solution toreplace the Hooghoudts approximation method for theequivalent depth by anexact solution. A comparison between this solution andthose of Lovell andYoungs (1984) and Hooghoudt (1940) showed that theexact solution proved tobe very accurate and efficient solution. The mainobjective of this study isto verify an accurate depth of the impermeable barrierand an effectiveradius of drain pipes which should be used in thedesign process using theexact solution.A field investigation was conducted in a study area of33,138 ha in theNorthern Delta of Egypt within Daqahliya Governorate.The results indicatethat a 5 m depth instead of infinity for theimpermeable layer in Nile Deltaand an effective radius of 90 mm should be used in thedesign process. Theuse of the exact solution for equivalent depth is acrucial issue especiallywith the high rate of on-going drainage projects inEgypt.