Comparison of Crop Contamination by Microorganisms during Subsurface Drip and Furrow Irrigation

This study was conducted to compare subsurface drip irrigation (SDI) with furrow irrigation (FI) in crop contamination with microbial-contaminated water irrigation. Escherichia coli, Clostridium perfringens, and coliphage PRD-1 were added to water used to irrigate cantaloupe, lettuce, and bell pepper. Samples of produce, surface, and subsurface (10?cm) soil for each irrigation system were collected on Days 1, 3, 5, 7, 10, and 14 after the application of the study microorganisms. Overall, greater contamination of produce occurred in FI plots than in SDI plots. The microorganisms were detected on the surfaces of cantaloupe and lettuce, but were never recovered on the bell peppers. The greatest amount of contamination occurred with PRD-1 on cantaloupe. The study microorganisms survived longer in the subsurface soil than the soil surface. PRD-1 showed greater persistence than E. coli in soil, while C. perfringens experienced little inactivation during the experiment periods. This study showed that subsurface drip irrigation has great potential to reduce health risks when microbial-contaminated water is used for irrigation water.     

Soil Hydraulic Properties Affecting Discharge Uniformity of Gravity-Fed Subsurface Drip Irrigation Systems

The use of subsurface drip irrigation (SDI) is increasing for many reasons, including its many agronomic advantages and the ability for safe application of wastewater to crops. In contrast to surface drip irrigation, soil hydraulic properties may affect SDI performance, particularly for new SDI systems designed to operate under low pressure (e.g., 2?m of head). This work introduces a new approach for solving problems of predicting discharge in SDI laterals. We accomplish this by coupling models of head loss in laterals and soil impacts on dripper discharge. The coupled model enables an evaluation of the performance of SDI laterals while changing inputs, such as the lateral diameter, length and slope, dripper nominal discharge and exponent, inlet pressure head, soil hydraulic properties, and soil spatial variability. This model is used to determine the coefficient of variation of discharge for two numerical comparisons.     

Using HYDRUS-2D Simulation Model to Evaluate Wetted Soil Volume in Subsurface Drip Irrigation Systems

Drip irrigation is considered one of the most efficient irrigation systems. Alternatively to the traditional drip irrigation systems, laterals can be installed below the soil surface. Realizing the subsurface drip irrigation (SDI), which recently has been increasing in use as a consequence of advances in plastics technology, making SDI equipment more affordable and long lasting. Due to its potential high efficiency SDI may produce benefits, especially in places where water is a limited source. As the use of SDI is relatively new, a better understanding of the infiltration process around a buried point source can contribute to increased water use efficiency and consequently the success of drip irrigation system. In addition, proper design and management of such a system needs the judicious combination of drip spacing, discharge rates, irrigation duration and time interval between consecutive irrigations. To this aim, numerical models can represent a powerful tool to analyze the evolution of the wetting pattern during the distribution and redistribution processes, in order to explore SDI management strategies, to set up the duration of irrigation, and finally to optimize water use efficiency. In the paper the suitability of the HYDRUS-2D simulation model is verified, at the scale of a single emitter, on the basis of experimental observations, with the aim to assess the axis-symmetrical infiltration process consequent to subsurface drip irrigation. The model was then applied in order to evaluate the main dimensions of the wetted soil volume surrounding the emitter during irrigation as a function of time and initial soil water content. The investigation, carried out in a sandy-loam soil, showed the suitability of the model to well simulate infiltration processes around an emitter during irrigation. Model application allowed also, for the examined soil, to evaluate the emitter spacing accounting for the maximum soil depth to irrigate.     

Procedures for Determining Maximum Emitter Discharge in Subsurface Drip Irrigation

One problem associated with subsurface drip irrigation (SDI) is the reduction in discharge resulting from soil-water back-pressure at the emitter outlets. An experimental setup was made to measure emitter discharge and pressure at the emitter outlet in different soils. Experiments were carried out with 2–24??L/h noncompensating and compensating emitters, operating at a constant lateral pressure of 10?m. Emitter discharge was reduced to a range of 2–10% for noncompensating models and to less than 1% for compensating models. Soil pressure ranged from 0.15–2.07?m. Laboratory conditions were simulated with HYDRUS-2D/3D. Experimental values of discharge and soil pressure showed good agreement with estimated values. Finally, maximum emitter discharge to limit the decrease of discharge was determined for an operating pressure of 10?m. For a 10% decrease, considering a constant radius of the spherical cavity in the soil, maximum emitter discharge was 2.35??L/h for loamy soil and 12.44??L/h for sandy soil for noncompensating emitters, and 10.73 and 54.51??L/h, respectively for compensating emitters. These values increased when considering a cavity radius variable with emitter discharge.     

Residential Water Savings Associated with Satellite-Based ET Irrigation Controllers

A mixed landscape irrigation study was conducted on 27 residential sites in Las Vegas to quantify water savings associated with satellite irrigation controllers. Seventeen sites were equipped with evapotranspiration-based (ET) satellite irrigation controllers and ten sites were designated as control sites and retrofitted with nonET-based irrigation controllers. Results showed that 13 of 16 ET-based controller sites saved water compared to four of ten of the nonET-based control sites. When all control sites were grouped together, a statistical difference occurred between the control and ET-based groups (ET-based controller=+20% savings) (p<0.05). Results from this study indicated that water savings were not because of deficit irrigations at the expense of the landscape plant material. Eighty-one percent of the variation in the total outdoor water use could be described by the total turfgrass area at each site. Such results would suggest that turfgrass limitations have merit, if the grass being restricted is tall fescue growing in an arid environment.     

Water Distribution in Laterals and Units of Subsurface Drip Irrigation. II: Field Evaluation

The performance of drip irrigation and subsurface drip irrigation (SDI) laterals has been compared. Two emitter models (one compensating and the other noncompensating) were assessed. Field tests were carried out with a pair of laterals working at the same inlet pressure. A procedure was developed that recorded head pressures at both lateral extremes and inlet flow during irrigation. Both models showed similar behavior and soil properties affected their discharge. On the other hand, the performance of a field SDI unit of compensating emitters was characterized by measuring pressures at different points and inlet flow. Finally, the distribution of water and soil pressure in the laterals and the unit were predicted and irrigation uniformity and soil pressure variability were also determined. Predictions agreed reasonably well with the experimental observations. Thus, the methodology proposed could be used to support the decision making for the design and management of SDI systems.     

Sensor-Based Automation of Irrigation on Bermudagrass, during Wet Weather Conditions

New technologies could improve irrigation efficiency of turfgrass, promoting water conservation and reducing environmental impacts. The objectives of this research were to quantify irrigation water use and to evaluate turf quality differences between (1) time-based scheduling with and without a rain sensor (RS); (2) a time-based schedule compared to a soil moisture sensor (SMS)-based irrigation system; and (3) different commercially available SMS systems. The experimental area consisted of common bermudagrass [Cynodon dactylon (L.) Pers.] plots (3.7?m×3.7?m), located in Gainesville, Fla. The monitoring period took place from July 20 to December 14, 2004, and from March 25 to August 31, 2005. SMS-based treatments consisted of irrigating one, two, or seven days a week, each with four different commercial SMS brands. Time-based treatments with or without RS and a nonirrigated treatment were also implemented. Significant differences in turfgrass quality among treatments were not detected due to the sustained wet weather conditions during the testing periods. The treatment with the rain sensor resulted in 34% less water applied than that without the rain sensor (2-WORS) treatment. Most SMS brands recorded irrigation water savings compared to 2-WORS, ranging from 69 to 92% for three of four SMSs tested, depending on the irrigation frequency. Therefore, SMS systems represent a promising technology because of the water savings that they can achieve during wet weather conditions while maintaining acceptable turfgrass quality.     

SDI Dripline Spacing Effect on Corn and Soybean Yield in a Piedmont Clay Soil

A subsurface drip irrigation (SDI) system was installed in the Piedmont of North Carolina in a clay soil in the fall of 2001 to test the effect of dripline spacing on corn and soybean yield. The system was zoned into three sections; each section was cropped to either corn (Zea mays L.), full-season soybean [Glycine max (L.) Merr.], or winter wheat (Triticum aestivum) double cropped to soybean representing any year of a typical crop rotation in the region. Each section had four plots; two SDI plots with dripline spacing at either 1.52 or 2.28 m, an overhead sprinkler irrigated plot, and an unirrigated plot. There was no difference in average corn grain yield for 2002–2005 between dripline spacings or between either dripline spacing and sprinkler. Irrigation water use efficiency (IWUE) was greater for sprinkler irrigated corn than for either SDI treatment and there was no difference in IWUE in soybean. Water typically moved laterally from the driplines 0.38 to 0.50 m. SDI yield and IWUE increased relative to sprinkler yields and water use efficiency in the second and third year of the study. This may suggest that initial fracturing of the heavy clay soil during SDI system installation and subsequent settling of the soil affected water distribution.     

Impact of Salinity on MS-2 Sorption in Saturated Sand Columns—Fate and Transport Modeling

This research investigated the sorption and transport of MS-2 in saturated sand under a wide range of salinities using one-dimensional column experiments. The salinity varied from 0 ppt (fresh water) to 30 ppt. The MS-2 in the fresh water showed very weak adsorption due to having the same negative charge as the sand. Increasing the salinity concentrations dramatically enhanced MS-2 adsorption. The MS-2 breakthrough revealed the existence of reversible and irreversible sorption sites in the sand. Salinity increased MS-2 attachment by compressing the double layers of MS-2 and reversible sorption sites. The salinity also changed some reversible sorption sites into irreversible sorption sites by reversing to positive surface charges of silica powder. An advection-dispersion-sorption model with a two-site reversible-irreversible kinetic sorption was developed to describe MS-2 breakthrough under different salinity conditions. The sorption parameters were estimated and their independence was evaluated by minimizing the total squared error of the MS-2 data. The proposed model showed good agreement with the experimental data for a wide range of salinity levels from fresh water to near seawater. The strong sorption shown in the MS-2 breakthrough at high salinity levels above 8 ppt was able to distinguish the proposed model from other sorption models. This study promotes the understanding of the viral sorption with salinity and provides a useful model for coastal management of viral migration in saline coastal groundwater.     

Sensor-Based Automation of Irrigation on Bermudagrass during Dry Weather Conditions

Overirrigation of lawns with limited resources of potable water has increasingly become an issue for the state of Florida. A previous study showed that soil moisture sensors systems (SMSs) could lead to irrigation water savings during relatively wet/normal weather conditions. This research, as a follow-up comparison, was conducted under dry weather conditions. The first objective was to statistically evaluate the water savings potential of different commercially available SMSs during the first half of 2006. In the second half, the objectives were to quantify irrigation water use and to evaluate turfgrass quality differences among: (1) a time-based irrigation schedule system with and without a rain sensor; (2) time-based schedules compared to SMS-based systems; and (3) SMS-based systems under different irrigation frequencies. The experimental area was located in Gainesville, Fla. and consisted of common bermudagrass [Cynodon dactylon (L.) Pers.] plots. Four commercially available SMSs (brands Acclima, Rain Bird, Irrometer, and Water Watcher) were used to bypass scheduled irrigation cycles when the soil water content at the 7- to 10-cm depth was above field capacity. Time-based treatments with and without rain sensor feedback were set up as comparisons for irrigation depth applied, and a nonirrigated treatment for turf quality comparison purposes was implemented. Due to the dry weather conditions and/or infrequent rain events during the experiment, the nonirrigated plots (as well as a broken SMS treatment) resulted in turfgrass quality below the minimum acceptable level. The rest of the treatments had at least minimum acceptable turf quality. The treatment with rain sensor resulted in 13 to 24% less water applied than without the rain sensor treatment. Most SMS-based treatments resulted in significant irrigation water savings compared to the treatment without rain sensor, which ranged from 16 to 54% in the first half, and from 28 to 83% in the second half of 2006, for three of four SMS brands tested.     

Water Distribution in Laterals and Units of Subsurface Drip Irrigation. I: Simulation

A complete methodology to predict water distribution in laterals and units of subsurface drip irrigation (SDI) is proposed. Two computer programs have been developed for the hydraulic characterization of SDI; one for laterals and the other for units. Emitter discharge was considered to depend on hydraulic variability, emitter’s manufacture and wear variation, and soil pressure variation. A new procedure to solve the hydraulic calculation of SDI looped network has been established. Moreover, spatial distribution of soil variability was estimated by a geostatistical modeling software that is coupled with the computer programs. Thus the evaluation and performance of laterals and units of SDI can be addressed by changing input variables such us: length and diameters of laterals; coefficients of emitter’s discharge equation; coefficient of variation of emitter’s manufacture and wear; local losses at the emitter insertion; inlet pressure; and soil hydraulic properties and its spatial variability. Finally, the methodology has been applied to different scenarios, and some recommendations are outlined for the selection of emitter discharge and inlet pressures.     

Evaluating Bioretention Hydrology and Nutrient Removal at Three Field Sites in North Carolina

Three bioretention field sites in North Carolina were examined for pollutant removal abilities and hydrologic performance. The cells varied by fill media type or drainage configuration. The field studies confirmed high annual total nitrogen mass removal rates at two conventionally drained bioretention cells (40% reduction each). Nitrate-nitrogen mass removal rates varied between 75 and 13%, and calculated annual mass removal of zinc, copper, and lead from one Greensboro cell were 98, 99, and 81%, respectively. All high mass removal rates were due to a substantial decrease in outflow volume. The ratio of volume of water leaving the bioretention cell versus that which entered the cell varied from 0.07 (summer) to 0.54 (winter). There was a significant (p<0.05) change in the ratio of outflow volume to inflow volume when comparing warm seasons to winter. Cells using a fill soil media with a lower phosphorus index (P-index), Chapel Hill cell C1 and Greensboro cell G1, had much higher phosphorus removal than Greensboro cell G2, which used a high P-index fill media. Fill media selection is critical for total phosphorus removal, as fill media with a low P-index and relatively high CEC appear to remove phosphorus much more readily.     

A novel neurotrophic pyrimidine compound MS-818 enhances neurotrophic effects of basic fibroblast growth factor

MS-818 (2-piperadino-6-methyl-5-oxo-5, 6-dihydro (7H) pyrrolo [2,3-d]pyrimidine maleate), a newly synthesized heterocyclic pyrimidine derivative, promotes neurite outgrowth in neuronal cell lines. The survival-promoting effect of MS-818 on cultured neurons isolated from mouse cortices was examined. MS-818 promoted neuronal survival by inhibiting apoptosis in a dose-dependent manner. MS-818 treatment also activated mitogen-activated protein kinase (MAPK) of the extracellular signal regulation kinase 2, as demonstrated by Western blot analysis. The MAPK activation level in the cultures treated with MS-818 was almost equivalent to that in cultures treated with nerve growth factor but was less than that in cultures treated with epidermal growth factor and basic fibroblast growth factor (bFGF). MAPK was activated within 3 min after the addition of MS-818, and its activity level returned to baseline within 120 min. Its activation was protein kinase C independent. We further investigated the effect of concurrent treatment with MS-818 and bFGF on neuronal survival. MS-818 enhanced the neuronal survival-promoting effect of bFGF in shifting the half-maximally effective dose from 2.1 ng/ml to 0.036 ng/ml in the sigmoidal dose effect of bFGF and permitted nearly maximum MAPK activation. The enhancement by MS-818 of the neuronal survival-promoting effect of bFGF was accompanied by sustained activation of MAPK to a degree that far exceeded, in magnitude and duration, the cooperative effect of MS-818 and bFGF. These results indicate that MS-818 promotes neuronal survival and enhances the neurotrophic actions of bFGF through stimulation of synchronous signals that may elevate MAPK levels within neurons.     

MS-551 and KCB-328, two class III drugs aggravated adrenaline-induced arrhythmias

We investigated the proarrhythmic effects of MS-551 and KCB-328, class III antiarrhythmic drugs using adrenaline-induced arrhythmia models in halothane anaesthetized, closed-chest dogs. In the control period, adrenaline, starting from a low dose of 0.25 to up to 1.0 microg/kg/50 s i.v., was injected to determine the arrhythmia inducing dose and the non-inducing dose. After MS-551 or KCB-328 administration, the adrenaline injection was repeated and the interval between the injection and the occurrence of arrhythmia (latent interval), the changes in arrhythmic ratio (as calculated by dividing the number of ventricular premature contraction by the number of the total heart rate) and the severity of arrhythmia were observed. MS-551 infusion, 1 mg/kg/30 min, decreased the heart rate (HR) by 16% (P<0.01) and prolonged the QTc interval by 20% (P<0.01). During the 30 min of MS-551 infusion, arrhythmias occurred in three out of seven dogs (torsades de pointes (TdP) type VT in one dog). After these arrhythmias disappeared, MS-551 decreased the latent interval of the adrenaline arrhythmias produced by the inducing dose (30+/-2 s compared with 43+/-3 s of the control interval, P < 0.05), increased the arrhythmic ratio (P<0.05) and induced arrhythmias by non-inducing adrenaline doses (P<0.05). Effect of a new class III drug KCB-328 infusion, 0.3 mg/kg/30 min, was compared witih MS-551 using the same model. KCB-328 decreased the HR by 21% (P<0.01) and prolonged the QTc interval by 25% (P<0.01). During the 30 min of infusion, arrhythmias occurred in five out of seven dogs (TdP in two dogs). KCB-328 also decreased the latent interval of the adrenaline arrhythmias produced by the inducing doses (31+/-3 s compared with 49+/-7 s of the control period, P<0.05), but did not significantly alter the arrhythmic ratio. Adrenaline induced TdP only after MS-551 or KCB-328 was administered, i.e. after MS-551, 1 mg/kg/30 min, 3/7 versus 0/7 in the control; KCB, 0.3 mg/kg/30 min, 3/7 versus 0/7 in the control. To examine the direct arrhythmogenic effect of MS-551 and whether an adrenergic mechanism plays some role on this arrhythmogenesis, a bolus injection of MS-551, 3 mg/kg, was injected either without pre-treatment or after pre-treatment with propranolol 0.3 mg/kg. MS-551 induced arrhythmias in five out of seven dogs (TdP in one dog). Also in the propranolol pre-treated dogs, MS-551 induced arrhythmias in five out of seven dogs (TdP in 1 dog). In conclusion, these observations indicate that MS-551 and KCB-328 induced arrhythmias and intensified proarrhythmic effects of adrenaline, MS-551 being stronger than KCB-328 at the same QTc prolonging doses. The direct arrhythmogenic effect of MS-551 was not influenced by beta-blocker treatment.     

Evaluation of Water Retention Functions and Computer Program “Rosetta” in Predicting Soil Water Characteristics of Seasonally Impounded Shrink–Swell Soils

Soil water retention is a critical factor influencing irrigation decisions and hence agricultural crop yields. However, information on soil water retention characteristics (SWRC) is seldom available for irrigation planning, crop yield modeling, or hydrological simulations, especially for problematic soils, such as seasonally impounded shrink-swell soils. As large scale direct measurement of SWRC is not viable due to a number of reasons, researchers have developed pedotransfer functions (PTFs) to estimate SWRC from easily measured soil properties, such as texture, organic matter content, bulk density, etc. However, PTF applicability in locations other than those of data collection has been rarely reported. One of the most recent PTFs that has shown overall reasonable predictions in evaluation studies is Rosetta, a numerical code for estimating soil hydraulic parameters with hierarchical pedotransfer functions. Relatively, the development of large databases makes it one of the widely used PTFs. If validated for spatial application, it has immense use potential in countries like India, where data on soil hydraulic properties are seldom available, a deficiency that hampers better simulations in processes, like partitioning runoff and infiltration, assessing evapotranspiration, irrigation scheduling, etc. Rosetta is also relatively flexible allowing estimation of hydraulic properties from easily available minimum input of textural fractions. This study was conducted to evaluate (1) an applicability of four widely used soil water retention functions to describe SWRC; and (2) the computer program Rosetta for its validity. Statistical indices, i.e., root mean square error (RMSE), mean absolute error, maximum absolute error, and degree of agreement (d) were computed to evaluate “goodness-of-fit” of the four functions to the measured SWRC data. These indices were also used to compare measured SWRC with estimates of SWRC by Rosetta. For soil samples collected from 41 profiles, 175 SWRC were measured in the laboratory. The van Genuchten function fitted relatively better (RMSE = 0.052?m3?m?3) to SWRC of clay soils, whereas the Brooks–Corey (BC) function was better in expressing SWRC of clay loam and sandy clay loam soils with RMSE = 0.06 and 0.07?m3?m?3, respectively. Campbell and Cass–Hutson (CH) functions were of intermediate value. Worst performing functions were BC (clay soils), Campbell (clay loam), and CH (sandy clay loam) with corresponding RMSE = 0.059, 0.065, and 0.077?m3?m?3. Estimates of two important points on the SWRC curve, i.e., field capacity and permanent wilting point were predicted with relatively better accuracy for clay and sandy clay loam soils by all the four functions. RMSE and d ranged from 0.027?to?0.043?m3?m?3 and from 0.73 to 0.88 for clay soils. Corresponding values for sandy clay loam soils were 0.008?–0.019?m3?m?3, and 0.92–0.98. However, in clay loam soils, only two functions were found suitable. Estimates of SWRC obtained by applying hierarchical rules in Rosetta were reliable (RMSE<0.05?m3?m?3). Magnitude of average RMSE increased progressively in clay loam, clay and sandy clay loam soils (0.028<0.035<0.042?m3?m?3). The study established that SWRC of the “Haveli” soils could be estimated using generic PTF and thus information that is prerequisite in simulating hydrological processes occurring in seasonally impounded soils could be acquired.     

Topical SDZ GLC-756, a novel dopamine D-1 antagonist and D-2 agonist, lowers intraocular pressure in conscious rabbits

OBJECTIVE: To investigate the longitudinal changes in serum HIV RNA, and to clarify whether the viral load early in infection has a predictive value for the clinical outcome; also, to correlate viral phenotype at seroconversion and changes in CD4 cell counts with viral burden. DESIGN: Twenty seroconverters with HIV isolates available at seroconversion had HIV RNA quantified by polymerase chain reaction (PCR) at seroconversion and thereafter every 6 months. Mean follow-up time was 65 months. Patients were classified according to viral phenotype at seroconversion, time to AIDS progression, serum viral load within the first year (less or more than 1.5 x 10(4) copies/ml). RESULTS: High viral load at seroconversion was followed by a significant decline within the first months (P < 0.0005). Decline to < 1.5 x 10(4) copies/ml was correlated with slower progression to AIDS (P < 0.05). A correlation between the rate of CD4 decline and the median viral load during the ensuing viral load plateau phase was also shown (P < 0.05). Subsequent to this phase the viral burden increased. Rapid progressors had higher viral load than slow- or non-progressors; this was particularly pronounced late in infection. Harbouring syncytium-inducing (SI) virus at seroconversion was associated with faster progression to AIDS than non-SI (NSI; P < 0.005). The increased in vitro replication rate of SI over NSI was not translated into significantly higher serum HIV RNA. CONCLUSION: Serum HIV RNA is high around the time of seroconversion. A significant decline within the first months hereafter is followed by a plateau phase, which in turn is followed by an increase in HIV RNA. HIV RNA early in infection has a predictive value for the clinical outcome. The increased virulence of SI over NSI virus did not translate into significantly higher HIV RNA values.     

Water Table Management to Improve Drainage Water Quality in Semiarid Climatic Conditions of Iran

A lysimeter study was conducted in the field in Karaj, Iran to investigate the effects of water table management on water quality of subsurface drainage effluents. Drain volumes, nitrate-N concentration, phosphorus concentration, and electrical conductivity of drain effluents were monitored during the growing seasons of alfalfa (Medicago scutellata). Totally 12 lysimeters consisted of four treatments were used in this study, of which nine of them were equipped with subirrigation (SI) and the other three with free drainage (FD) systems. Annual alfalfa (Medicago scutellata) was planted in all lysimeters. Water table levels were kept at 30 cm (SI30), 50 cm (SI50), and 70 cm (SI70) below the soil surface in SI-lysimeters and more than 100 cm below the soil surface in FD-lysimeters. The results of this 2-year study showed a significant reduction in nitrate-N concentrations in SI-lysimeters compared to FD-lysimeters. In 2005, the mean nitrate-N concentrations in drainage effluent were reduced by 84% in the SI30 and by 82% in the SI50, relative to FD. Similarly, in 2006, drain water depth and nitrate-N concentrations were significantly reduced relative to FD. The forage dry matter production from SI30 and SI50 were significantly higher than those from FD in both years. In 2006, the average of dry matter production was increased by 69 and 89% by the SI30 and SI50, respectively, relative to FD. The average electrical conductivity of drainage water was reduced in SI lysimeters compared to FD lysimeters that meet Iranian standard level (3 dS/m). There are no statistically significant differences in phosphorous concentration in drainage water of different treatments. Finally, the results of this 2-year study indicate that the water table management practices are economically and environmentally feasible in Iran in order to have a sustainable agriculture.     

Migratory behaviour and desiccation tolerance of protostrongylid nematode first-stage larvae

Migration of first-stage larvae (L1) from faeces to soil is a crucial stage in the life-history of protostrongylids transmitted via land snails. Migration of Muellerius cf. capillaris and a Cystocaulus sp. L1 from fresh Nubian ibex (Capra ibex nubiana) faeces (48-50% water content, W.C.) to substrate soils (at 100% r.h., 26 degrees C) was measured experimentally using dry (3 +/- 1% W.C.), wet (31 +/- 0.43% W.C.) and flooded (48.4 +/- 2.45% W.C.) soils. The highest migration rates (90.4 +/- 1.6% migration) in both species occurred on flooded soils when the faecal pellet W.C. reached 90%. The next highest migration rates (43.2 +/- 3.6% migration, at 60% faecal W.C.) were on the wet soils and no migration occurred on dry soil or dry-substrate papers. Migration rates did not differ significantly (P > 0.05) between species. Active Theba pisana were not infected by M. cf. capillaris L1 on dry infested soils, but were infected following rehydration of the same soils. By day 10, L1 of M. cf. capillaris demonstrated lower survival rates in water and in 97% and 76% r.h. (74.5%, 15.2% and 1.9%, respectively) than the Cystocaulus sp. (97.5%, 43.8%, 43.3%) and Protostrongylus sp. (97.9%, 43.2%, 23.8%, P < 0.05). All three nematodes had a remarkably high survival rate (> 99% overall survival, by day 10) when exposed directly to 0% r.h. at 23 degrees C. Results demonstrate the ability of L1 to survive extreme desiccation through anhydrobiosis. Migration of L1 from faeces to soil can take place only during rains which coincide with peak activity of land snails in desert habitat.     

Comparison of HYDRUS-2D Simulations of Drip Irrigation with Experimental Observations

Realizing the full potential of drip irrigation technology requires optimizing the operational parameters that are available to irrigators, such as the frequency, rate, and duration of water application and the placement of drip tubing. Numerical simulation is a fast and inexpensive approach to studying optimal management practices. Unfortunately, little work has been done to investigate the accuracy of numerical simulations, leading some to question the usefulness of simulation as a research and design tool. In this study, we compare HYDRUS-2D simulations of drip irrigation with experimental data. A Hanford sandy loam soil was irrigated using thin-walled drip tubing installed at a depth of 6 cm. Three trials (20, 40, and 60 L?m?1 applied water) were carried out. At the end of each irrigation and approximately 24 h later, the water content distribution in the soil was determined by gravimetric sampling. The HYDRUS-2D predictions of the water content distribution are found to be in very good agreement with the data. The results support the use of HYDRUS-2D as a tool for investigating and designing drip irrigation management practices.