Iran Agricultural Research
Year:2000 | Volume:19 | Issue:2|Papers Count:9

To evaluate the soil salinity hazard in Ramhormoz area located in Khuzestan province, disjunctive kriging was used. Assessment was made through a series of salinity risk map. Disjunctive kriging is a non-linear geostatistical estimation technique which provides minimum estimation variance. Moreover, it allows calculating the conditional probability that some critical threshold is exceeded. The results of mapping soil salinity at depth 0-50 cm indicate that about 45% of the interpolated sites show an EC higher than 16 dS m-1. About 18% of the whole area was interpolated with an EC less than 4 dS m-1 the lowest EC values were found mainly in the areas around and along the river occupied by soils of river alluvial origins, while, the areas with very high EC values are the places situated in the lowlands where two patches of marshes exist. To estimate the conditional probability some salinization thresholds, critical thresholds of 2, 4 and 8 dS m-1, were selected. Considering the threshold value of 2 dS m-1, almost the entire area shows the conditional probabilities of more than 0.5. It indicates that there is a severe salinity limitation in the entire area. Assuming that a probability level of 0.6 is acceptable, for about 40%, of the entire area the EC was found to be more than 4 dS m-1.

Fractal theory is increasingly being used to characterize aggregate size distributions of soils. Our purpose was to compare indirect number-size fractal dimension (Dn, a fitting parameter), mass-size fractal dimension (Dm), and mean weight diameter (MWD), as measures of soil aggregate stability. Samples of a calcareous silty clay soil (Calcixerollic Xerochrept) was treated with cationic, anionic and clay emulsion petroleum mulches and "krilium merloam" (krilium) which is a copolymer of vinyl acetate and maleic acid. Application amounts were 0, 0.5, 1.0 and 1.5 g kg-1 on dry mass basis. Assuming cubic aggregates of constant dry density, Dn was estimated from cumulative size-frequency distribution data plotted on a log log scale and Dm was estimated from cumulative mass-size distribution data in the same manner. Dn and Dm decreased with increasing amount of mulch applications indicating an increase in aggregate stability as a result of the addition of the mulch. The increase was most pronounced for the krilium, indicating that this chemical was most effective for increasing aggregate stability. Application of MWD, Dn and Dmmay lead to different conclusion’s in the assessment of the effectiveness of the various chemicals for improving soil aggregate stability. For less effective chemicals (petroleum mulches) Dn values (a fitting parameter) were a better indicator of differences in fragment distributions. while for more effective chemicals (Le., krilium) MWD showed the differences in fragment distribution better than Dn and Dm.A~e1ition of krilium at amounts greater than 0.5 g kg-1 might have resulted in aggregates with complete fragmentation properties, while the aggregates of other treatments did not show this behavior. The Dn (a fitting parameter) may be used to describe the fractal behavior of the soil fragments with MWD greater than 0.67 and 1.17 mm for petroleum mulch and krilium applications, respectively. However mass-size fractal dimensions failed to show the effects of various rates of petroleum, mulches on the fragment size distributions.

In developing countries such as Iran, where many factors of production are- in short supply, inefficient use of resources is particularly undesirable. Analysis of efficiency can help farmers to identify the possibilities for increasing -output as well as conserving resource use. The objective of this study was to investigate the technical efficiencies for a sample of wheat farms situated in the Ferydan region, Isfahan province. A stochastic frontier production function model was estimated. Parameters of the stochastic frontier production function and the parameters associated with determinants of technical inefficiencies were simultaneously estimated for the sample farmers. Results of this study demonstrated that the production of wheat can be increased by 33% at the current levels of resource use if the technical efficiency gap among farmers is suitably narrowed. Factors affecting the estimated level of technical inefficiency of production of wheat farmers included levels of education and farming experiences.

Sources of resistance to Watermelon mosaic virus (WMV), Zucchini yellow mosaic virus (ZYMV), and two local isolates of Cucumber mesaic virus (CMV) as the most destructive viruses to melon (Cucumis melo L.) fields in Iran were investigated. This study evaluated the resistance of melon germplasm under high disease pressure achieved with natural inoculations by indigenous aphid vector in the field, mechanical inoculations in the greenhouse, and then field comparison of resulting resistant and tolerant cultivars (cvs.) by natural and mechanical inoculations. The .majority of genotypes used in this study was open-pollinated (OP). Some selfed (S1) seeds and F1 hybrids were also included. The results indicated that most of the melon cvs were susceptible to both natural infection of cucurbit viruses in the field and mechanical inoculation in the greenhouse. However, melon cvs. 'Magotalena Vertbrod', 'Soski' and 'Bahramabadi' (OPs) were immune to ZYMV. Melon cvs. 'Galicum' (S1), 'Latifah-1' (S1), 'Tashkandi', (OP) and 'Khorasgani' (OP) were resistant to CMV and WMV under both greenhouse and field conditions. Melon cvs. 'Baghkomeh Lenjan', 'Oshtorjan', 'Lenjan', 'Firozan', 'Shahd-Shiraz', 'Ardian' and 'Latifah' (OPs) were tolerant considering both infection type and fruit yield reduction traits. Virulence of CMV#1, CMV#2, WMV and ZYMV differed significantly, where CMV#1 was the most virulent type having the highest mean of disease severity (3.59). The reassessment of the progenies of resistant and tolerant cvs with doubly infected plants in the field, provided evidence that the sources of resistance or tolerance found in the earlier field and greenhouse germplasm evaluations are heritable.

In a survey conducted in 1998, 15 species of natural enemies attacking cypress tree mealybug, Planococcus vovae (Nasonov) were found in Shiraz, Iran. These included two parasitoids, 4nagyrus pseudococci (Girault) and Dusmetia fascipennis (Noys & Hayat). The most common predators included Exochomus spp., Hyperaspis polita Weise, Nephus bipunctatus Fursch, Chrysoperla carnea (Stephens), Suarius fedtschenkoi (McLachlan), Dicrodiplosis manihoti Harris- and Geocoris quercicola Linnavuori. The effectiveness of these natural enemies was reduced by the hyperparasitoids, Marietta picta (Andre) and Chartocerus spp., by the parasite Homalotylus ephippium Ruschka attacking coccinellids, and by the parasites Cheiloneurus ceroplastis Ishii, Ooencyrtus kuvanae (Howard), Isodromus atriventris Ashmead, I. aff. vinulus, Catolaccus crassiceps (Masi) and Pachyneuron concolor (Forster) attacking chrysopids.

The aerial parts of St. John's wort (Hypericum perforatuln L.) contain active substances that are used in antidepressive and wound healing drugs. The main purpose of this study was to determine the effect of harvest time on herb yield, hypericin and essential oil content of H. perfotatum. The herb of H. perforatum in full-bloom stage contained higher amount of hypericin (329 mg g-1 -in dry weight) than pre-bloom and fruit set stages (22 mg g-1 and 148 mg g-1, respectively). Essential oil content at full-bloom stage was higher (0.35 .m1 100g-1 dry weight) than pre-bloom and fruit set stages (0.12 and 0.18 ml 100g-1, respectively). The suitable time for harvesting of H. perfolatum- is, therefore, full-bloom stage to maximize hypericin and essential oil levels.

Transformation and neoformation of clay minerals as affected by various physiographic positions were studied in soils from semi-arid regions of Fars province in southern Iran. Soil samples were taken from control sections of soil profiles at various physiographic units. Clay specimens were prepared from soil samples. The clay mineralogy of specimens was analyzed by X-ray diffraction. Mica (illite), chlorite, smectite (montmorillonite), vermiculite, palygorskite, and interstratified illite-smectite and chlorite-smectite were recognized. The higher physiographic units contained more illite and chlorite, whereas the lower ones had a higher montmorillonite and palygorskite. This was further confirmed by changes in cation exchange capacity of soils. Inherited illite and chlorite were transformed to montmorillonite and vermiculite. It is possible that neoformation of montmorillonite and palygorskite from soil solutions has also occurred.

The chilling and heat-sum requirements of seven commercial almonds ['Managa' (early-bloom), 'Ne Plus Ultra' and' Azar' (mid to late-bloom), 'Sahand', 'A200', 'A230' and 'Shokofe' (late-bloom)] were studied in 1994- 96, with a view to assessing their adaptability under different climatic conditions. 'Sahand', 'A200' and 'A230' maintain their late blooming qualities because of their high chill and heat-sum requirements, and' Azar' is a middle-bloom cultivar with a medium chilling requirement and low heat-sum requirement. Therefore, this cultivar will probably flower late in warmer climates. 'Managa' can be grown in warmer climates with no problems due to its low chilling requirement and minimum heat requirement. 'Shokofe' is a late-blooming cultivar, despite its lower chilling and heat-sum requirements than 'Ne Plus Ultra' and therefore more compatibility studies will be required for various zones. 'Ne Plus Ultra' is not recommended for cold climates owing to its limited chilling and heat-sum requirements and early blooming.