Journal of Crop Production and Processing

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To determine the effects of field slope, emitter discharge, irrigation water volume and soil texture on soil moisture profile and soil surface wetted shape from a point source, field data were collected on three different soil types, three emitter discharges (4, 8, and 12 lph), four slopes (0, 2, 5, and 10%), and five irrigation water volumes (10, 20, 30, 40, and 50 liters) with three replications. The results showed that the surface-wetted area increases as the emitter discharge increases. The surface-wetted area decreased with a corresponding increase in emitter discharge in experimental fields with light-textured soils. In experimental fields with heavy textured soils and slopes greater than 5%, the changes in surface-wetted area due to the emitter discharge increases, were higher compared to slopes of less than 5%. Since, a higher emitter discharge would result in higher surface-wetted area, the results showed that for an equal volume of irrigation water, the soil moisture profile was deeper for lower emitter discharge. In general, the volume of wetted zone was higher for greater emitter discharges. It was found that as the volume of irrigation water increased, the volume of wetted zone would increase correspondingly. This effect is more prominent than that of emitter discharge. In general, the depth of wetting front was lower and the wetted surface area was greater for heavy textured soils as compared to the light textured soils. The wetted-surface area and the shape of wetting front in the direction of slope were affected by the soil infiltration, emitter discharge and volume of irrigation water where these effects were more critical in higher sloping lands.

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In this research, the presence of metalaxyl residues was studied in field-grown cucumber. Two different formulations of metalaxyl were used in the experiments. In the first experiment, cucumber plants were sprayed once and repeatedly by Ridomil-MZ 72 WP at 2.5 g/litre. In the second experiment, single and double applications of metalaxyl granule 5G were carried out at 5 g/m². Leaves and fruits were sampled at different times after each treatment and analyzed for metalaxyl residues by HPLC.

In leaf samples from single sprayed plots, metalaxyl residues declined rapidly following the treatment and more than 50% of the residues disappeared in the first two days, whereas in the leaf from single granule-applied plants, the residues increased during the first three weeks and then declined. Metalaxyl residues in cucumber sampled from single sprayed-plots were at a high level during the first three days after the spray and declined below the MRL (0.5 mg/kg) on the 7th day. In granule-applied plots, the residues increased during the first 7 days and the level below the limit was recorded 20 days after application. Residual values for plants sprayed with suspension showed a faster dissipation rate than granulated treatment. Metalaxyl recovered after three times of spraying and two times of granular application did not show any toxic accumulation of residues in fruit.

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Aggregation is an important temporal property of soil structure that is affected by intrinsic soil properties and also soil use and management. Aggregate stability has a strong influence on many processes in soil such as infiltration, aeration, strength, erosion, and soil’s ability to transmit liquids, solutes, gases, and heat. In this study, undisturbed soil specimens from 0-10 and 10-20 cm depths were sampled during summer 1999 from some regions in Iran including Golestan, Kermanshah, West Azerbaijan, and Mazendaran. After drying the samples in lab, the different sizes of aggregates were separated and the wet aggregate stability (WAS) and dispersible clay (DC) were determined on 2-2.8 mm aggregates according to Pojasok & Kay procedure (1990). The variance analysis of data showed significant differences among soils in all regions. The averages were compared by Duncan test to find the following order: Mazendaran > Golestan > Kermanshah > West Azerbaijan. Regression analysis of data of whole regions showed that the variability of aggregate stability was mainly explained by organic carbon content (R²=0.723 in P > 0.0001). The clay content had the greatest effect on aggregate stability in samples from Golestan while sand content had the greatest effect in samples from West Azerbaijan. The resulting equations from stepwise regression can be used to estimate aggregate stability from other soil variables in the study regions.

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The influence of the Sea Surface Temperatures (SSTs) on the seasonal precipitation over northern and southwestern parts of Iran was investigated. The warm, cold and base phases of the SSTs were defined and the median of precipitation during each of these phases (R_w, R_c and R_b, respectively) was determined. The magnitude of R_w/R_b, R_c/R_b and R_c/R_w were used as criteria for the assessment of the effects of the alternation of SST phases on seasonal precipitation. The results indicate that in association with cold SST phase, winter rainfall is above median over western and central parts of the coastal region, central and southern parts of Fars Province and all the stations studied in Khozestan Province. On the other hand, the prevalence of warm SST phase has caused about 20% decrease in winter precipitation over the Caspian Sea coastal area and northern parts of both Fars and Khozestan provinces. In association with warm SST phase in winter, precipitation during the following spring was found to be above normal for all the stations studied in the coastal region of the Caspian Sea. The highest sensitivity levels were found in Bandar- Anzali and Astara for which spring precipitation has increased by 80% due to the dominance of warm winter phase. However, the occurrence of boreal cold SST events causes shortage of precipitation in the eastern parts of the coastal areas along the Caspian Sea. A Possible Physical mechanisem justifying the influence of the Caspian Sea SST on the Precipitation variability was introduced. According to this mechanisem, temporal and spatial variability of the Siberian High is forced by the fluctuations in these SSTs.

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  This research was carried out to study the impacts of geomorphologic characteristics of claypan on land use and land degradation. Databank of the study area was constructed and digital terrain model of claypan was prepared. By using GIS techniques spatial distributions of the subsurface drainage network, sediment transportation index and wetness index were calculated. The results indicate that the depth to the claypan is between 0 (where the pan is exposed at the surface) to 605 cm. There are several depressions in the claypan which are filled by new sediments. Each depression has a catchment which is charged by the drainage water of its attributed lands. While a depression drains naturally or synthetically, the attributed soils over the depression are in non saline or moderate salinity condition otherwise, a marshland, a waterlogging area or a salt crust zone develops over there. The results also indicated that soil surface salinity is a function of depth to claypan and drainage condition of area. The trends of salinity extension are different for closed and open catchments and the depth to the claypan could be estimated using electrical conductivity. The results also show that analysis of microtopography of soil surface and soil stratification should be considered for designing irrigation and drainage networks.

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For an appropriate drip irrigation system design, a prediction of soil wetting pattern is needed for a given soil texture. The wetting pattern geometry is a key factor for emitter distance determination as well as crop type. The geometry of the wetting bulb is dependent on the parameters such as soil hydraulic properties, emitter discharge and the irrigation time. This study has been conducted in Albaji region in km 25 on the Ahvaz-Andimeshk road, in order to estimate the geometry of the wetting pattern under the point source trickle emitters in sandy soil with different discharge. The emitters were calibrated to provide 5, 10, 20, 30 and 40 liter per hour discharges. The maximum wetted soil surface and depth was measured by digging the irrigated soil. Two models were developed to predict wetted soil surface diameter and depth under a point source based on Buckingham's π theorem. The equations were calibrated by using the measured data. Then resulted scientific-empirical equations have been evaluated. Considering the maximum relative error of 14.3% and root mean square error of 3.8cm in estimation of the wetted soil surface diameter and depth, the models are recommended to estimate the geometry of the wetting bulbs with a high degree of accuracy, and can be used in designing and appropriate drip irrigation system management

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Soil physical and chemical properties, and test conditions might affect soil structural stability. In this study, the effects of test conditions as well as intrinsic soil properties on structural stability were investigated for selected soils from Hamedan Province. Mean weight diameter (MWD) and tensile strength (Y) of aggregates were determined by wet sieving method and indirect Brazilian test, respectively. The soil samples were pre-wetted slowly to matric suction of 200 kPa before the wet sieving. The pre-wetted samples were wet-sieved for 5, 10 and 15 min in order to simulate different hydro-mechanical stresses imposed on soil structure. Tensile strength of soil aggregates were also measured at air-dry and 500 kPa matric suction conditions. Short duration shaking (i.e. 5 min) could effectively discriminate the Hamedan soils in terms of structural stability due to their fairly low aggregate stabilities. The soil organic matter content had the highest impact on MWD followed by both clay and CaCO₃ content. The same was true for the Y values i.e. OM played the highest role in mechanical strength of soil aggregates. The highest coefficient of determination (R²) was obtained between Y and the intrinsic soil properties for matric suction of 500 kPa. The organic matter content had an important role in water and mechanically stable soil aggregates. The results indicated that short-duration wet sieving (i.e. 5 min) and measurements of tensile strength at matric suction of 500 kPa could be recommended for aggregate stability assessment in Hamedan soils