JWSS - Journal of Water and Soil Science

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During recent years, worldwide concern has been focused on the potential for contamination of surface waters and ground waters by agrochemicals in runoff and soil water from irrigated fields. Given this perspective, it is very important to correctly evaluate the levels of different agrochemicals in water, both from human toxicological and environmental viewpoints and to develop management strategies for reducing agrochemical loads to acceptable levels in the environment. The main objective of this study was to assess the qualitative changes of tailwater due to the use of agrochemicals and thereby to determine contamination loads. Four farms (A, B, C and D) were chosen in the Foumanat region in the F₂ unit in 1996. The areas of these fields ranged from 0.22 to 0.6 ha having a number of unequal successive basins with variable inflow and outflow rates.

 A quantitative analysis showed that the tailwater ratio in farms A, B, C and D ranged from 2 to 64% during the irrigation season. The outflow water was classified as C₃S₁. The changes in qualitative factors were not significant and did not follow any certain pattern during the irrigation season. The changes in SAR, EC, Cu, Zn, B, P, K and DO in the inflow and outflow waters were also insignificant. After fertilizer application, the increase in nitrogen concentration in the outflow was significant. The average pollution loads in the inflow and outflow were about 1618 and 1476 kg/day/ha, respectively. The remaining load in the rice fields was about 142 kg/day/ha, which was meaningful at 1% level. The fifth farm (E) located in Lahidjan was sprayed with diazinon. Water samples were analyzed each day for diazinon residues for 10 days after application. Sample analysis showed that the concentration of the insecticide was 93.08 mg/l immediately after application and gradually reduced to 0.98 mg/l ten days after spraying.

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This paper studies the structure of cost and production of rice using cross section data from rice farming in Guilan in 1997. A translog cost function is specified for this purpose and estimated, using Iterative Seemingly Unrelated Regressions for both the short and the long run where all factors are taken to be variables. The results of the study are as follows:

1. Neither in the short-run nor in the long-run is the possibility of technical substitution among the factors of production strong.

2. Own and cross price elasticity of demand for inputs are positive but less than one, hence limited substitutability among inputs is possible as the result of a change in input prices.

3. As the structure of production of rice in Guilan exhibits increasing returns to scale, increased allocation of land to the production of rice could result in a lower price of the product.

4. Inputs are not homogeneous, therefore, not all producers are faced with the same price for the same input. Nevertheless, the cost of production has been lower for those farmers who have paid a higher price for an input. Therefore, the higher price for inputs is more than that compensated by the quality of each input in the production process.

5. Due to the inelasticity of the demand for rice with respect to prices, a large price increase is required to stimulate farmers to allocate more resources to the production of rice.

6. Since the possibility of substitution among inputs is limited, a large increase in relative prices is required in order to change the structure of rice production.

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The soil potassium status and effect of soil physical and chemical properties on it were investigated using 109 surface soils (0-30cm) from four regions in Guilan province. Neutral molar ammonium acetate extractable K (K-NH₄OAc), boiling molar nitric acid extractable K (K-HNO₃) and water soluble K were determined. Results showed that CEC and clay were normally frequency distributed while distribution frequency of other variables such as silt organic carbon and pH were not normal and have significant skew and kurtosis. In addition sand, K-NH₄OAc and K-HNO₃ has logarithmic normal distribution. Water-soluble potassium was affected by sand, pH, O.C and K-NH₄OAc (R²_a=0.73**). Ammonium extractable potassium was affected by soluble potassium, non-exchangeable potassium and CEC (R²_a=0.72**). Boiling nitric acid was affected by exchangeable potassium and silt (R²_a=0.55**). Geographic distribution of K-NH₄OAc data shows amount of it in central parts of Guilan, particularly Sepidrood river watershed is more than other regions. Fomanat region soils have the less clay, CEC, K-NH₄OAc and K-HNO₃. According this study about 68.8 percent of Guilan soils was classified in the range of medium to very low potassium status.

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Cultivation of a second crop in paddy fields of Guilan province is a strategy for optimum use of land, supporting family economy and increasing oil-seed production. However, this is impeded under high rainfall and waterlogging conditions. To enhance second-crop cultivation in paddy fields, surface drainage is inevitable. The surface drainage practices should be performed with minimum costs, least time span and least variations of the land. In the present research, longitudinal surface drains were constructed with a spacing of 2, 4, 6, 8 and 10 m (depth of 20 cm), with and without 1-m lateral drains (depth of 10 cm) in Rice Research Institute, Rasht, Iran. The experiment was conducted in a complete randomized block design with three replications. Canola (Brassica napa), variety PF, was cultivated as a second crop after rice. The results showed that the effects of drain spacing on seed yield, days to maturity, number of plants per m², and also the effects of lateral drainage on seed yield, plant height, residual N, days to maturity, and number of plants per m² are significant (P<0.01). Highest yield (2493 kg/ha) was obtained from longitudinal drains 4 m apart, with lateral drainage drain spacing of 6 and 2 m had acceptable yields, too (2241 and 1817 kg/ha, respectively). For treatments without lateral drainage, 2-m drain spacing had the highest yield (1324 kg/ha). Considering all the expenses for drainage construction, it was found that net benefit of longitudinal drain spacing of 4 and 6 m was twice the costs. Since the rainfall in Nov., Dec., and Jan., 2000, was higher than the 20-year average rainfall of the same months, it was concluded that the results of this experiment may be recommended in the years with a rainfall less than the year 2000.

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Fire blight caused by Erwinia amylovora, is a serious disease of pome fruits in many areas in the world which causes evaluative necrosis. Indeed, E. amylovora can invade the whole tree solely by internal progression through the host tissues. In this research, symptoms of necrotic shoots and exudates production on infected pear trees in different areas of Guilan province (Astaneh Ashrafieh, Lahijan and Kiashahr) were surveyed. Samples were taken from infected tissues of diseased trees. For isolation of bacterial causal agent, the infected tissues were crushed in pepton water, then 100µl of the extracts were cultured on Sucrose Nutrient Agar (SNA) and Luria Berthani (LB) containing Cyclohexamid antibiotic (50 µg / ml). The isolated bacteria were rod-shaped , gram negative and facultatively an-aerobic. The bacteria produced Levan on media including sucrose , but could not produce fluorescent pigments on King’s B medium. All strains made hypersensitive reaction on tobacco leaves. All isolates were oxidase , nitrate, urease and indole negative and were not able to rot potato tuber slices, produce H₂S and grow in 36 °C. The isolates could use citrate, acetoin, sorbitol and trehalose and their gelatin test was positive. Based on morphological, biochemical, physiological characteristics and production of a 937 bp with specific primer Ea1 and Ea2 in PCR method, the strains were identified as E. amylovora. This is the first report of the existence of this bacterium on pear fruit trees in Guilan province.

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Since more than 75% of the rice fields in Iran are located in the Northern provinces i.e. Mazandaran, Guilan, and Golestan identifying the crop water requirement of rice fields is essential for water resources planning in the Northern provinces. The objective of this research was to ascertain the crop water requirement of two rice cultivars namely Hashemi and Khazar in Guilan province during 1389 growing season. Four iron barrels with diameter of 56 cm were used as lysimeters to grow the cultivars mentioned. According to a simple volume balance approach the crop water use of the four lysimeters were determined during the growing season. The elements of volume balance approach such as the depths of drainage, precipitation, and irrigation were recorded daily and the average of 5-day and 10-day periods were reported. The daily rice crop water use during the growing season was found to range from 2.4 to 6.3 mm/day with a seasonal crop water use ranging from 430 to 470 mm for Hashemi and Khazar cultivars, respectively. Daily reference evapotranspiration was computed by the FAO-Penman-Montith equation and accordingly rice crop coefficients were computed. The crop coefficient of Hashemi variety was found to be 1.1, 1.3, and 1.1 during the initial, mid, and end growth stages, respectively. In addition, the aforementioned parameters for Khazar variety were 1.2, 1.3, and 1.1.