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Cadmium (Cd) is a known hepato- and nephrotoxic pollutant and zinc (Zn) metalloproteins are important targets of Cd. Hence, the administration of Zn may mitigate Cd toxic effects. However, the interaction of Cd and Zn has been little investigated in the brain. Previously, we reported a protective effect of Zn on mortality caused by Cd in rats. Here, we tested whether the protective effect of Zn could be related to changes in brain Zn-proteins, metallothionein (MT) and δ-aminolevulinate dehydratse (δ-ALA-D). Male adult rats were daily administered for 10 days with Zn (2 mg kg−1), Cd (0.25 and 1 mg kg−1) and 0.25 mg kg−1 of Cd plus Zn and 1 mg kg−1 of Cd plus Zn. The body weight loss, food intake deprivation, and mortality occurred in 1 mg kg−1 of Cd, but Zn co-administration did mitigate these effects. The brain Zn content was not modified by treatment with Cd, whereas cerebral Cd levels increased in animals exposed to Cd. The administration of 0.25 mg kg−1 of Cd (with or without Zn) induced lipid peroxidation and decreased MT concentration, but 2 mg kg−1 of Zn and 1 mg kg−1 of Cd did not change these parameters. Brain δ-ALA-D was not modified by Cd and/or Zn treatments. Since the co-administration of Zn did not attenuate the changes induced by Cd in the brain, our results suggest that the protective effect of Zn on impairments caused by Cd in animal status is weakly related to a cerebral interaction of these metals.

Pentylenetetrazole (PTZ) is a common convulsant agent used in animal models to investigate the mechanisms of seizures. Although adult zebrafish have been recently used to study epileptic seizures, a thorough characterization of the PTZ-induced seizures in this animal model is missing. The goal of this study was to perform a detailed temporal behavior profile characterization of PTZ-induced seizure in adult zebrafish. The behavioral profile during 20 min of PTZ immersion (5, 7.5, 10, and 15 mM) was characterized by stages defined as scores: (0) short swim, (1) increased swimming activity and high frequency of opercular movement, (2) erratic movements, (3) circular movements, (4) clonic seizure-like behavior, (5) fall to the bottom of the tank and tonic seizure-like behavior, (6) death. Animals exposed to distinct PTZ concentrations presented different seizure profiles, intensities and latencies to reach all scores. Only animals immersed into 15 mM PTZ showed an increased time to return to the normal behavior (score 0), after exposure. Total mortality rate at 10 and 15 mM were 33% and 50%, respectively. Considering all behavioral parameters, 5, 7.5, 10, and 15 mM PTZ, induced seizures with low, intermediate, and high severity, respectively. Pretreatment with diazepam (DZP) significantly attenuated seizure severity. Finally, the brain PTZ levels in adult zebrafish immersed into the chemoconvulsant solution at 5 and 10 mM were comparable to those described for the rodent model, with a peak after a 20-min of exposure. The PTZ brain levels observed after 2.5-min PTZ exposure and after 60-min removal from exposure were similar. Altogether, our results showed a detailed temporal behavioral characterization of a PTZ epileptic seizure model in adult zebrafish. These behavioral analyses and the simple method for PTZ quantification could be considered as important tools for future investigations and translational research.

Hydraulic conductivity of soil is strongly dependent on soil structure, which can be degraded during wetting and leaching. It was hypothesised that this structural degradation is dependent on initial aggregate size distribution and soil texture. The general aim of this study was to investigate the effects of aggregate sizes and soil textures, and their interactions, on the structural degradation and saturated hydraulic conductivity ([K.sub.s]) of smectitic soils under different saline and sodic conditions. The studied soils were clay and loamy sand soils with low (~4.5) or high (~10) exchangeable sodium percentages (ESP), and with aggregate sizes in the ranges: (i), Introduction Soil hydraulic conductivity (K), which determines the ability of soil to conduct water, is an important parameter governing the soil phase of the hydrological cycle, affecting solute transport and [...]

Hepatic encephalopathy (HE) arises from acute or chronic liver diseases and leads to several problems, including motor impairment. Animal models of chronic liver disease have extensively investigated the mechanisms of this disease. Impairment of locomotor activity has been described in different rat models. However, these studies are controversial and the majority has primarily analyzed activity parameters. Therefore, the aim of the present study was to evaluate locomotor and exploratory behavior in bile duct-ligated (BDL) rats to explore the spatial and temporal structure of behavior. Adult female Wistar rats underwent common bile duct ligation (BDL rats) or the manipulation of common bile duct without ligation (control rats). Six weeks after surgery, control and BDL rats underwent open-field, plus-maze and foot-fault behavioral tasks. The BDL rats developed chronic liver failure and exhibited a decrease in total distance traveled, increased total immobility time, smaller number of rearings, longer periods in the home base area and decreased percentage of time in the center zone of the arena, when compared to the control rats. Moreover, the performance of the BDL rats was not different from the control rats for the elevated plus-maze and foot-fault tasks. Therefore, the BDL rats demonstrated disturbed spontaneous locomotor and exploratory activities as a consequence of altered spatio-temporal organization of behavior.

Formation of a depositional seal is common in soils subjected to rainfall or sprinkler or surface irrigation; however, studies on its hydraulic properties are scarce. In this study, the effects of clay mineralogy, exchangeable sodium percentage (ESP), electrolyte concentration, and pH on the hydraulic properties of depositional seals were investigated. A silt loam packed in columns was leached with 5 g [L.sup.-1] suspensions of reference montmorillonite, illite, and kaolinite with various ESPs (0-100), electrolyte concentrations ( Abbreviations: ESP, exchangeable sodium percentage; SAR, sodium adsorption ratio

The open tank paradigm, also known as novel tank diving test, is a protocol used to evaluate the zebrafish behavior. Several characteristics have been described for this species, including scototaxis, which is the natural preference for dark environments in detriment of bright ones. However, there is no evidence regarding the influence of "natural stimuli" in zebrafish subjected to novelty-based paradigms. In this report, we evaluated the spatio-temporal exploratory activity of the short-fin zebrafish phenotype in the open tank after a short-period confinement into dark/bright environments. A total of 44 animals were individually confined during a 10-min single session into one of three environments: black-painted, white-painted, and transparent cylinders (dark, bright, and transparent groups). Fish were further subjected to the novel tank test and their exploratory profile was recorded during a 15-min trial. The results demonstrated that zebrafish increased their vertical exploratory activity during the first 6-min, where the bright group spent more time and travelled a higher distance in the top area. Interestingly, all behavioral parameters measured for the dark group were similar to the transparent one. These data were confirmed by automated analysis of track and occupancy plots and also demonstrated that zebrafish display a classical homebase formation in the bottom area of the tank. A detailed spatio-temporal study of zebrafish exploratory behavior and the construction of representative ethograms showed that the experimental groups presented significant differences in the first 3-min vs. last 3-min of test. Although the main factors involved in these behavioral responses still remain ambiguous and require further investigation, the current report describes an alternative methodological approach for assessing the zebrafish behavior after a forced exposure to different environments. Additionally, the analysis of ethologically-relevant patterns across time could be a potential phenotyping tool to evaluate the zebrafish exploratory profile in the open tank task.

To link to full-text access for this article, visit this link: http://dx.doi.org/10.1016/j.jenvman.2005.10.014 Byline: N. Dudai (a), E. Putievsky (a), D. Chaimovitch (a), M. Ben-Hur (b) Keywords: Vetiver; Mediterranean region; Soil conservation; Runoff Abstract: In spite of the advantages of Vetiver grass in light of environmental aspects, this plant is not used in the Mediterranean region. The objectives of the present study were: (i) to elucidate growth parameters and establishment of Vetiver under Mediterranean conditions suitable for its various environmental applications; and (ii) to develop management practices for growing vetiver under Mediterranean conditions. In greenhouse experiments conducted under controlled conditions it was found that, in general, increasing the minimum/maximum temperatures to 21-29[degrees]C significantly increased plant height. In the Mediterranean region, this range of air temperatures is obtained mainly during the summer, from June to September. For air temperatures up to 15-23[degrees]C the effect of day length on plant height was insignificant, whereas in air temperature >15-23[degrees]C, the plant heights under long day conditions were significantly higher than under short day. The number of sprouts per plant increased exponentially with increasing air temperature, and was not significantly affected by the day length at any air temperature range. In open fields, the heights of irrigated vetiver plants were significantly higher than those of rain-fed plants. It was concluded that, once they were established, vetiver plants could survive the dry summer of the Mediterranean region under rain-fed conditions, but they would be shorter than under irrigation. Cutting or burning of the plant foliage during the spring did not improve the survival of vetiver during the dry summer. In order to obtain fast growth of vetiver and to increase the possibility of its using the rainwater, the plants should be planted in the winter, during February and March. However, under this regime, the vetiver plant cannot be used as a soil stabilizer during the first winter, because the plant is still small. In contrast, under irrigation it is advantageous to plant vetiver at the beginning of the summer; the plant then has sufficient time to grow and develop before the beginning of the winter, so that its effect as a soil stabilizer in the following wet winter could be maximal. It was found that vetiver could grow in a wide range of substrates, such as: sandy soil, loamy sand, clay soil, crushed limestone, sandy clay loam, and tuff/peat mixture. Author Affiliation: (a) Section of Aromatic and Medicinal Plants, Newe Ya'ar Research Center, ARO, P.O. Box 1021, Ramat Yishay 30095, Israel (b) Institute of Soil, Water and Environmental Sciences, the Volcani Center, ARO, P.O. Box 6, Bet Dagan 50250, Israel Article History: Received 5 March 2005; Revised 21 July 2005; Accepted 6 October 2005 Article Note: (footnote) [star] Contribution from the Agricultural Research Organization, The Volcani Center, 102/2005 series.

High-frequency drip irrigation supplies water and nutrients at a rate that is close to plant uptake, thus enhancing growth and production. In light of water scarcity in arid regions, marginal water is increasingly considered as a resource for agricultural production. The objective of this study was to investigate the combined effects of pulsed irrigation and water salinity on the response of the soil--plant system. As a test crop, bell pepper (Capsicum annuum L.) was cultivated in a screenhouse and drip irrigated daily (D) and at high frequency (P) with saline (S) and fresh (F) water. Simultaneous monitoring of meteorological, physiological, soil physical, plant and soil chemical, and yield data was performed during the experiment. Most physiological parameters were negatively affected by high water salinity. No consistent effect of the irrigation frequency was found on the overall season, although pulsed irrigation led to higher plant weight and leaf area at the early stages of plant growth. The distinct patterns of soil water content for the two irrigation frequencies are presented. Salinity in the root zone was higher under pulsed irrigation, an observation that is supported by measured leaf chloride content and tensiometer readings indicating that the once daily application may have more efficiently removed salts from the top soil. Yield, fruit weight, and irrigation water use efficiency (IWUE) were highest under once daily irrigation with fresh water. High-frequency irrigation led to higher Mn concentrations in leaves and fruits and increased concentrations of Cl, N, and P in leaves, confirming earlier conclusions on improved P mobilization and uptake under pulsed irrigation.

Seal formation at the soil surface during rainstorms reduces rain infiltration and leads to runoff and erosion. An increase in soil sodicity increases soil susceptibility to crusting, runoff, and erosion. Surface application of dissolved polyacrylamide (PAM) mixed with gypsum was found to be very effective in decreasing seal formation, runoff, and erosion. The objective of this study was to investigate the effects of surface application of dry granular PAM (20 kg [ha.sup.-1]) mixed with phosphogypsum (PG) (2 and 4 Mg [ha.sup.-1]) and that of PG alone on the infiltration rate (IR), runoff, and wash erosion from four smectitic soil types (ranging in clay content between 10 and 62% and sodicity level between exchangeable sodium percentage [ESP] 2 and 20) exposed to simulated distilled water rainstorms. Increasing ESP from 5 to 20 in the loamy sand decreased final IR from 14 to 2 mm [ha.sup.-1] and increased runoff and wash erosion in the control; similar trends but of different magnitude were noted in the other soil types. Spreading PAM mixed with PG or PG alone was effective in maintaining final IR > 12 mm [ha.sup.-1], low runoff, and wash erosion levels compared with their control. Use of PAM mixed with PG resulted in higher final IR and lower runoff levels than PG alone in all four soils studied. Conversely, with respect to soil erosion, PAM mixed with PG was more effective than PG alone in reducing wash erosion from the loamy sand and clay and had comparable effects on soil loss in the loam. It was concluded that for rain-fed agriculture, spreading of dry granular PAM mixed with PG was more effective than PG alone in reducing runoff and erosion in soils varying in texture and sodic conditions.

The use or effluent for irrigation could affect tile chemical and hydraulic properties of soils due to its high salt and organic matter (OM) content, and, consequently, the rainfall--infiltration--runoff--erosion relationships during the subsequent rainy season. This study investigates the effects of long-term effluent irrigation on soil chemical properties, seal formation, infiltration, and soil loss under rainfall. Simulated rainfall (85 mm) was applied to (i) air-dried or (ii) prewetted clay and sandy soils front plots that had been irrigated with fresh water (FW) or efflueut for >10 yr. Effluent irrigation increased the total OM content and tile exchangeable sodium percentage (ESP) of the soils. The cumulative infiltration in FW- and effluent-irrigated clay soils was 6.5 and 5.6 mm, respectively, in the initially dry soils, and 52.3 and 51.5 mm, respectively, in the prewetted soils. In the FW- and effluent-irrigated sandy soils, the corresponding values of cumulative infiltration were 79.5 and 44.7 mm, and 85.0 and 56.3 mm, respectively. In the sandy soil, the higher sodium adsorption ratio (SAR) values in the leachate of effluent-irrigated soil led to greater clay dispersion, which enhanced seal formation, reduced infiltration, and increased soil loss. In the clay soil, slaking was the main process involved in seal formation, neglecting the possible deleterious effect or effluent irrigation. When slaking was prevented, the SAR values in the leachate of the effluent-irrigated soil decreased during rainfall and were similar to those of the FW-irrigated soil at the end of the applied rainfall amount. This was probably due to the exchange of adsorbed Na with soluble Ca, which minimized the differences in clay dispersion, infiltration, and soil loss. Therefore, in the clay soil, aggregate slaking might be the main process involved in seal formation and affecting infiltration and erosion. These results show that the effect of effluent irrigation on infiltration, runoff, and soil loss depends on the soil type (amount of clay and CaC[O.sub.3]) and the dominant mechanisms of seal formation. Therefore, to prevent a possible deleterious effect on soil structure, it is necessary to identify sensitive areas and soils before the application of effluents for irrigation.

Previous studies about the effect of antecedent moisture content (AMC) on seal formation have shown contradictory results. We hypothesize that this controversy is related to differences in slaking during wetting. The objectives were to analyze the effects of: (i) clay content on aggregate stability and slaking; (ii) clay content and slaking on seal formation and interrill erosion under various wetting rates (WR) and AMC under simulated rain. Aggregate stability was determined on six smectitic soils from Israel with clay content from 80 to 630 g [kg.sup.-1]. In the rain simulator, soils with 230, 410 and 620 g [kg.sup.-1] clay were prewetted with WR = 1 and 5 mm [h.sup.-1] to AMC = 0.25 and 0.5 of field capacity (FC), prior to the application of 80 mm of rain. Aggregate stability and slaking by fast WR increased with increase in clay content. In soils with 230 and 410 g [kg.sup.-1] clay, raindrop impact was enough to disintegrate the aggregates and sealing was not affected by WR and AMC. Conversely, in the soil with 620 g [kg.sup.-1] day, seal formation increased with slaking caused by fast wetting. Thus, final infiltration rate of the clay soil with AMC = 0.5 FC and WR = 1 mm [h.sup.-1] was 11.1 mm [h.sup.-1] compared with 6.0 mm [h.sup.-1] in the air-dry soil (fast wetting by rain). The effects of WR and AMC on soil loss were similar to their effect on runoff but more pronounced. The relation between wetting process and clay content should be considered when predicting soil erosion in smectitic soils.

The objectives of this study were to investigate (i) the effect of soil organic matter (OM) contention the mechanisms that form a seal, and (ii) the OM content and aggregate size interactions in seal properties, infiltration rate (IR), and soil loss. Two samples of sandy loam (Humic Dystrudept) designated low-OM soil (2.3% by weight OM) and high-OM soil (3.5% OM) were studied. Aggregate sizes

The objective of this study was to investigate the effect of the interaction between organic matter (OM) content and aggregate size on the mechanisms that degrade the soil structure and on the saturated hydraulic conductivity ([K.sub.s]). Two samples of sandy loam (Humic Dystrudept) containing 2.5 and 3.5% OM, referred to as low-OM soil and high-OM soil, respectively, were collected from adjacent fields. Dry samples were sieved to obtain aggregate sizes of 93 and 2.9% and

Soil organic matter can be divided into solid (SOM) and water-dissolved (DOM) fractions; both of which can associate with herbicides. The objective was to examine the effects of DOM in applied solutions on atrazine adsorption in soil containing various SOM contents. A sandy loam with low (0.14%, Soil L), medium (1.2%, Soil M), or high (6.7%, Soil H) total organic matter, and artificial soil (Soil A) with no organic matter were used. These soils were treated with several different atrazine concentrations, dried, and extracted with water; the DOM concentrations in these extracts were 0, 10.1, 41.1, and 156.5 mg [L.sup.-1], respectively. These extracts and the untreated soils were used in batch experiment. The distribution coefficients ([K.sub.d]) for atrazine of Soils L, M, and H under mixing with Soil A extract were 0.19, 0.52, 2.51, respectively, indicating that the higher the SOM content, the higher the atrazine affinity to the soil solid phase. The effects of the DOM concentration on atrazine adsorption were estimated from the ratios ([R.sub.d]) between the [K.sub.d] for applied solution with no DOM and those for applied solutions containing DOM. [R.sub.d] > 1 indicates that the DOM decreases the herbicide adsorption. The [R.sub.d] values for Soils L, M, and H, each soil mixed with its extract, were 2.68, 1.93, and 1.07, respectively. In contrast, in the case where the soil was mixed with a solution that contained a higher DOM concentration than the soil extract, an increase in the DOM concentration in the applied solution decreased the [R.sub.d] value. This was probably because of adsorption of DOM-atrazine complexes on the SOM.

Under limited water resources, modern irrigation methods tend to save water and improve water and salt regimes within the root zone. This study deals with the combined effects of water application methods and tillage practices on water and salt distributions, runoff production, and soil loss in a field irrigated with moving irrigation systems (MIS). An experiment was conducted in a cotton (Gossypium hirsutum L. cv. Sivon) field at Hazorea, Israel, where the main soil type is vertisol (Typic Chromoxerets). Sprinkling (SP) and flooding (FL) MIS, and conventional (CT) and microbasin (MB) tillage, were compared in terms of runoff and soil loss from runoff microplots (5 [m.sup.-2]), soil water content and salinity distribution with depth, yield, and plant height. Under SP conditions, no runoff and soil loss were obtained for either tillage practice. In the FL/CT treatment, the mean runoff and soil loss were about 25% of the irrigation water and 0.59 kg [m.sup.-2]. The FL/MB treatment reduced the runoff and soil loss to 5.8% and 0.02 kg [m.sup.-2], respectively. The soil water contents in the SP treatments were generally lower than in the FL treatments, especially in the 0.1- to 0.6-m soil layer. No significant differences in the soil salinity, plant height, and seed-cotton yield were observed between the treatments. Microbasins tillage reduces water losses under flooding MIS to a point where they become practically similar to those obtained under sprinkler MIS. It can potentially lead to lower water losses if the microbasins storage capacity is matched to the water application rate, to avoid runoff.

Soil mineralogy and texture have substantial effects on aggregate stability and, therefore, may influence infiltration rate (IR) and soil loss under rainfall. The objective was to study the effects of soil mineralogy and texture on crust micromorphology, infiltration, and erosion. Five soils with differing properties were subjected to 80 mm of simulated rainfall. The aggregate stability of these soils was determined by the fast wetting method. The mean-weight diameters of the particles after the fast wetting were 2.8 mm in the clayey kaolinitic soil, 0.25 and 0.31 mm in the clayey and sandy loam montmorillonitic soils, respectively, and 0.84 and 0.87 mm in the clayey nonphyllosilicate soils. The final IR was 20.5 mm [h.sup.-1] in the clayey kaolinitic soil and [less than or equal to] 9.3 mm [h.sup.-1] in the remaining soils. Scanning electron microscope (SEM) observations indicated that the kaolinitic soil had a thin crust (~0.1 mm) containing large particles (~0.1 mm), whereas the montmorillonitic soils had thicker crusts (>0.2 mm) comprising either small (~0.02 mm) particles with a very developed washed-in zone underneath or large (~0.2 mm) ones with fine material between them. The crust layer in the nonphyllosilicate soils was ~0.2 mm thick and composed of fine particles ~0.01 mm. The high aggregate stability and the low dispersivity of the kaolinitic soil, which minimized soil detachment, and its low runoff, which minimized its transport capacity, limited the soil loss to 0.33 kg [m.sup.-2], whereas the low aggregate stability and high runoff of the montmorillonitic soils contributed to their soil losses of 1.24 and 1.14 kg [m.sup.-2]. The intermediate aggregate stability and the high runoff of the nonphyllosilicate soils accounted for their intermediate soil losses of 0.75 and 0.8 kg [m.sup.-2].

Smallholder farmers in arid and semi-arid regions use indigenous soil and water conservation (ISWC) techniques, such as trash lines and stone lines spaced about 15 m apart across the slope. This work evaluated the effects of size of trash lines and decreasing the space between trash or stone lines to 2 m on runoff, erosion, and corn and cowpea yields. Big trash line (BTL), small trash line (STL), and stone line (SL) techniques, and a control (no ISWC technique) were evaluated in 12 runoff plots (2 by 6 m each) with 10% slope in a semi-arid area in Kenya, during 5 consecutive rainy seasons. The ISWC techniques significantly (P ≤ 0.05) decreased runoff and soil loss, and increased corn and cowpea yields, compared with the control treatment in most of the rainy seasons. The BTL was, in general, the most effective technique; no consistent differences were found between the STL and SL techniques. In BTL, STL, SL, and control, the seasonal average runoff for each treatment was 25, 31, 29, and 51 mm, respectively; the seasonal average soil loss was 0.23, 0.33, 0.3, and 0.67 Mg/ha, respectively; and the seasonal average biomass (grain and stover of corn and cowpea) was 4.8, 4.0, 4.0, and 2.5 Mg/ha, respectively. The seasonal biomass increased linearly and significantly (P ≤ 0.01) with increasing water infiltration. As more water infiltrated, more water was available for crop production, and the yield was higher. Additional keywords: trash lines, steep land, seal formation., Introduction Runoff and soil erosion are serious and widespread land degradation problems in many parts of the world (Hudson 1992). In Kenya, runoff and soil erosion have been identified as [...]

Vertisols markedly swell and disperse when wet because of the high percentage of montmorillonite in the soil. We hypothesized that soil bulk compaction, time since soil wetting (aging), and raindrop impact affect seal formation, soil permeability, and salt leaching of Vertisols. Vertisol (Typic Chromoxererts) samples with exchangeable Na percentages (ESP) of 0.4 and 11.8 were subjected to simulated rainfall of deionized (DW) and saline (SW) (electrical conductivity [EC] = 5 dS[m.sup.-1]) waters with 0 and 18.1 J [mm.sup.-1] [m.sup.-2] impact energies. In a Vertisol without aging (0.5 h of prewetting) and under zero compaction, subjected to DW and SW rainfall, seal formation controls the soil permeability. Under DW rainfall, the final infiltration rates (FIR) of the sealed and unsealed Vertisol samples were 6 and >44 mm [h.sup.-1] at ESP 0.4, and 5 and 17 mm [h.sup.-1], respectively. Four days of aging without compaction, followed by DW rainfall, increased the FIR of unsealed soil to 37 and to >44 mm [h.sup.-1] at high and low ESP, respectively, and that of sealed soil to 12 and 14 mm [h.sup.-1] at high and low ESP, respectively. Subjecting wet soil to pressure up to 800 kg [m.sup.-2] decreased the unsealed Vertisol FIR under DW rainfall to 8.9 and 27 mm [h.sup.-1] at high and low ESP, respectively. Seal formation and bulk compaction had little effect on salt leaching in the low-ESP soil. Under bulk compaction or seal formation, the high-ESP soil leachate EC decreased from 10.7 to 9.0 dS [m.sup.-1] after 300 mm of DW rain.

The effectiveness of synthetic polymers as soil conditioners was found to depend on polymer properties. We hypothesized that the polymer penetration and movement into the aggregate are important factors in reduction of surface sealing. The effect of nonionic (P-101), cationic (CP-14), and anionic [Complete Green (CG)] commercial polymers on infiltration rate (IR) and aggregate formation was studied in a sandy loam (Typic Rhodoxeralf). Amounts of 25, 50, and 75 kg [ha.sup.-1] of each polymer were spread across the soil surface. After air drying, the surface was subjected to 68 mm of distilled water with impact energy of 18.1 J [mm.sup.-1] [m.sup.-2] using a rainfall simulator. Soil particle association was studied in 10% (w/v) soil suspension with polymer concentration ranging from 0 to 50 g [m.sup.-3]. Viscosity values 3.3 109, and 165 mPa s were determined in 5 g [L.sup.-1] of P-101, CP-14, and CG solutions at shear rate of 27 [s.sup.-1], respectively. The final IR values were 63 to 30 mm [h.sup.-1] at P-101, 18 to 24 mm [h.sup.-1] at CP-14, and 18 to 30 mm [h.sup.-1] at CG, compared with 8 mm [h.sup.-1] in untreated soil. The critical time values in suspensions with different concentrations of polymer were 4.3 to 2.7 min for P-101, 1.0 to 3.4 min for CP-14, and 1.0 min for CG. The critical time indicates the size of the aggregate formed in a suspension; the lower the critical time, the larger the aggregates. It was suggested that because the particle surfaces are exposed to polymer molecules in suspension, the large molecule of CG could tie more suspended particles to form aggregates. The greater effectiveness of P-101 in preventing sealing was probably due to its ability to penetrate into aggregates, because of its small molecular size and low viscosity in solution.

The effects of soil surface dispersion and seal formation on erosion are analyzed. Dispersive soils are susceptible to seal formation, and are therefore more erodible than nondispersive soils, which have high infiltration rates. Moreover, spreading five Mg per hectare phosphogypsum on the soil surface decreased the soil loss sharply from the dispersive soils and moderately from the nondispersive soils. Lastly, a Water Erosion Prediction Project model is developed to quantify the erosion parameters.

The addition of low concentrations of polyacrylamide (PAM) and polysaccharide (PSD) to irrigation water resulted in high water infiltration rates. However, the polymers had little residual effect in subsequent irrigations with plain water. This was attributed to erosion of the treated layer. Lower levels of PAM were needed to produce the desired effects on infiltration as compared to PSD. PAM-treated soil had significantly lower erosion losses than PSD-treated soil. This was attributed to PAM's longer molecule and limited adsorption, which resulted in more cohesive aggregation and higher erosion resistance.

Development of an impermeable layer at some depth beneath the soil surface and the presence of a high groundwater level are common phenomena in the Yizre'el Valley, Israel. The main objective of this study was to determine the salt and water distributions and salt leaching in a field irrigated by sprinklers, under nonisotropic and high groundwater level conditions. A field experiment was conducted in a cornfield (Zea mays L.) on a Vertisol (Typic Chromoxerets) with subsurface drains. The electrical conductivity (EC) of the irrigation water was 2.5 dS [m.sup.-1]. The variations in water table level, in EC of soil solution and soil saturation paste, and in gravimetric water content along the field were determined at different times. Likewise, corn yield from various sites across the field was determined at the end of the growing season (August). The water table level increased sharply in the winter to 49.5 m, and then decreased continuously in the summer despite the irrigation. The EC increased in the downhill direction, more sharply in the deeper soil layers. In the upper part of the field, the average EC in saturation paste in the 0- to 1.2-m soil layer was 1.1 dS [m.sup.-1] in March (end of the rainfall season) and 2.1 dS [m.sup.-1] in August. Conversely, in the lower part of the field, the ECs in March and August were 4.4 and 3.7 dS [m.sup.-1], respectively. A linear reduction of the corn yield with increasing EC was observed. The relatively low level of the groundwater at the upper part of the field allowed vertical salt leaching by the rainfall. Conversely, the rise of the saline (EC [approximately equal to] 20 dS [m.sup.-1]) groundwater in the lower part of the field in the winter with lateral salt movement increased the soil EC. Decline of the water table in the latter part in the summer allowed vertical leaching of salt by the irrigation water.

Application of saline water using moving irrigation systems (MIS) can affect the water and salt distribution in the field and the crop yield because of runoff formation. The objective of this study was to determine the effects of tillage and water application methods on the distributions of water content, salt concentration in soil, and corn (Zea mays L.) yield under irrigation with saline water by MIS. The experimental site was located in a forage corn field in the Negev, Israel. Three tillage treatments were studied: (i) conventional tillage (control); (ii) microbasin; and (iii) diked furrows (dike). The control and the microbasin plots were irrigated with sprinkler MIS, and the dike plots with flooding MIS. The studied parameters were measured in five sampling sites located 25 m apart along the slope. The average dry canopy yields of the whole slope in the control, dike, and microbasin treatments were 21.7, 25.3, and 30.6 Mg [ha.sup.-1], respectively, and their coefficient of variance (CV) values along the slope were 7.9, 5.7, and 3.5%, respectively. In the control treatment, soil water content increased from 0.12 kg [kg.sup.-1] upslope to 0.1.9.0 kg [kg.sup.-1] downslope. In contrast, no slope effect on soil water content was found in the microbasin and dike treatments. The electrical conductivity (EC) of the 0- to 0.3-m soil layer in the control treatment increased in the downslope direction from 2.0 to 4.0 dS [m.sup.-1]. Conversely, in the microbasin and dike treatments, no consistent trend of the EC was observed with slope, and their average values were 3.4 and 7.0 dS [m.sup.-1], respectively. It was suggested that these yield differences were related to the differences in the distribution of the soil water content and the salt concentration in soil within the field.