فصلنامه تحقیقات مهندسی کشاورزی
سال دوازدهم شماره 3 (پاییز 1390)

Irrigation management includes cut-off dates, water volume and irrigation frequency control to influence the yield and post-harvest status of garlic. In this study, the effect of cut-off dates and irrigation levels on garlic were investigated over three years using a completely randomized block arranged in a split plot experimental design consisting of three levels of irrigation (75%, 100%, 125% water use) as the main plot and three irrigation cut-off dates (current date of cut-off, one week prior to and one week subsequent to the prevalent date for Hamedan garlic farms) as the sub-plot with three replications. After harvesting, the clove weight, bulb diameter, clove and skin numbers and yield were measured. The greatest and least clove weights were obtained for 125% water used in the third (47.5 g) and first (39.8 g) cut-off dates, respectively. Clove weight and bulb diameter for the third date increased and skin number decreased. The greatest yield was obtained for 125% water and at the first cut-off date (10450 kg/ha). The differences were not significant for the other treatments, except for 75% water used at the third cut-off date (8622 kg/ha). The greatest WUE was found for 75% water at the first cut-off date (9.7 kg/m3). As a result of this study, the 75% level of irrigation and the first cut-off date were shown to be the most suitable.

Soil dispersion is a phenomenon where soil particles float when they are exposed to water and are carried away by the force of seepage. Various laboratory methods, including double hydrometer, Emerson, and pinhole tests and the Sherard chemical method have been used to evaluate soil dispersion potential. Despite the fact that soil dispersion is caused by its chemical composition, the results obtained from the chemical methods, especially from the Sherard method, do not match the results of the pinhole test. In this study, the role of existing anions in the dispersion potential of clayey soils was studied. Natural soil samples were collected from different regions of Iran and artificial soil samples were created by adding different percentages of sodium chloride, sodium carbonate, sodium sulfate, and sodium polyphosphate to a non-dispersive soil. The physical, chemical, and index properties of all samples were determined and the Sherard method and pinhole test were employed to determine the dispersion potential. The results obtained from the tests showed that soil dispersion, which is a physico-chemical phenomenon, was caused by a combination of existing anions and cations in the soil, both in type and quantity. It was also found that the Sherard chemical method did not determine soil dispersion correctly since the role of some anions, especially chloride, was neglected. Among the existing anions in the soil, chloride, as opposed to sodium, acted as a flocculating factor.

In the management of river basins, prediction of river water quality is essential to maintain water quality within standard limits. This study performed a time-series analysis of the prediction of chlorine concentration and electrical conductivity time series data for the period of 1991-2005 from Sefidrood River in northern Iran. The seasonal prediction of chlorine and electrical conductivity time series data was done using the linear stochastic model known as the multiplicative seasonal autoregressive integrated moving average (SARIMA). Initially, Mann-Kendall and Box-Pierce tests were used to identify the trend and stationary state of the time series, respectively. The results showed that there was no significant trend in these time series, but that 12-month seasonal patterns were observed. As a result, seasonal patterns were removed from both time series data using first-order differencing. SARIMA modeling was performed in three steps: model identification, parameter estimation and diagnostic checking. Different models of SARIMA were identified according to the ACF and PACF time series results and the model with the minimum AIC criterion was selected. For parameter estimation, model parameters were estimated using a least squares optimization algorithm that minimized the residual sum of squares. The results of diagnostic checking then indicated that the residuals were independent, normally distributed and homoscadastic. The selected SARIMA model was then used to predict chlorine concentration and electrical conductivity time series data for 2003-2005. There was a good unanimity between the predicted and observed data. For model verification, the mean and variance of the predicted and observed data were compared. The RMSE for Cl and EC were 2.2 and 278.9, respectively. The results showed that there was no significant difference between the predicted and observed time series data. This study showed that the SARIMA model can be used reliably to predict chlorine concentration and electrical conductivity time series data in Sefidrood River.

Post-harvest management of potatoes is a major challenge in Iran. Approximately 30% of the harvest is lost after a few months of storage. The chemical methods for long term storage are not adequate to control deterioration and also produce undesirable side effects. To address this issue, a study on radiation preservation of potatoes was carried out. Agria potato bulbs were irradiated using beta beams at dosages of 0 (control) to 150 Gray and then kept in conventional storage for 7 months. Irradiation was done at 1, 4 and 8 weeks after the date of harvest. Every six weeks moisture content, reduced sugar, sprouted tubers and darkening of peeled potatoes were examined. The results showed that decreased sugar accumulation, sprouting, weight loss and darkening of peeled tubers irradiated at 120 Gray decreased more significantly (P ≤ 0.05) than for the less-irradiated tubers. Irradiation time had a significant effect on these parameters. The best results were obtained for potato tubers irradiated before one month after harvest. The effect of irradiation on nitrate content of the tubers was not clear. As the storage time increased, the moisture content of the tubers decreased and, conversely, the reduced sugar and sprouted tubers increased. This treatment is recommended as a method to decrease potato waste to less than 10%. None of the treatments are recommended for treating seed potato tubers.

The purpose of this research was to inhibit the proliferation of insects and microorganisms and to preserve the quality of semi-moistened figs. The microbiological, physical and chemical properties and storage pests of semi-moistened figs (cv. Sabz Stahban) in modified atmosphere packaging were evaluated after storage for 3 and 6 months at 25° and 40 C. The gas treatments tested were: 1) 74% N2 + 25% CO2 + 1% O2; 2) 49% N2 + 50% CO2 + 1% O2; 3) 24% N2 + 75% CO2 + 1% O2; 4) 95% vacuum; 5) control sample: 78% N2 + 0.3% CO2 + 21% O2. The effects of gas treatments on semi-moistened fig properties such as color, moisture, total count, mold and yeast, and acidity were insignificant. The effects of treatments were significant for storage pests, such as larva, after 3 months storage at 25°C. The most effective treatment for killing larva was 95% vacuum. Storage at 40°C was not suitable because of its adverse effect on the color and texture of the figs. It can be concluded that modified atmosphere packaging is a good replacement for methyl bromide.

Physical and cutting tests were performed at 70-day intervals on a variety of local garlic maintained at three different storage periods to determine the physical properties of garlic bulbs and cloves and the cutting properties of garlic cloves The height, mean width diameter, arithmetic mean diameter, geometric mean diameter, bulk density and sphericity of the bulbs were measured and determined. These values were, respectively, 27.81-28.72 mm, 36.11- 37.88 mm, 33.65-34.52 mm, 33.39-34.10 mm, 90.24%-92.48%, and 529.6-594.6 Kg/m. The length, width, thickness, arithmetic mean diameter, geometric mean diameter, sphericity, bulk density, particle density, porosity and volume for cloves were also calculated. The results showed that storage period has a significant effect on the mean width diameter, arithmetic mean diameter and bulk density of the bulbs and also on the length, bulk density, particle density, volume and arithmetic mean diameter of the cloves. Cutting tests are performed at three loading speeds and three storage periods. The maximum cutting force required to complete cutting of the cloves was 2.28-4.79 N and the mean energy required to complete cutting of the cloves per unit area was 17.297-29.270 mJ/mm2. The mean force required to complete cutting of the cloves per unit area was 1.442-2.98 N/mm2. Storage period had a significant effect on the cutting properties of the cloves.

Developing alternative technologies for the use of fossil fuels is necessary and inevitable. To meet this need, the SAPHT project developed an energy-efficient electric hybrid tractor for agricultural light operations. The energy source for SAPHT was in part solar and the rest was supplied from a grid. This research compared simulated and experimental field results for SAPHT. The results show that SAPHT is capable of substituting for I category tractors. Using the designated parameters, SAPHT can operate standard implements for 2-4 h daily; however, improved use of batteries would make it possible to increase the daily range more than three fold.

Several methods are used to decrease seed drying time and enhance the quality of dried seeds. In fluidization methods, good aeration occurs during the drying process. In this research, conditioned seeds with 20% d.b. moisture content were dried at 30°, 40°, 50° and 60 C using three bed conditions (fixed, minimum fluidized, fluidized). All experiments were done using a batch-type fluidized bed dryer and three replications. Temperature and bed changes in the dryer on canola seed drying kinetics were investigated. The cultivating properties of dried seeds, such as final germination percentage, emergence percentage, seedling leaf area index and seedling dry mass percentage were compared with naturally dried seeds as a control. Experimental results showed that temperature and seed bed changes had significant influences on the canola seed drying process. Suitable aeration was observed during and after minimum fluidized bed drying, which may save energy during the drying process. The fluidized seed bed decreased drying time more than 23% over the fixed bed. The fluidized resulted in about an 8% increase in drying time over the semi-fluidized seed bed. When the use of high temperature is limited for drying, fluidization at moderate temperatures can a suitable alternative for drying heat-sensitive materials. Drying at 30° and 40°C using semi-fluidized beds is a good choice for drying canola seeds. It did not have harmful effects on the canola seed cultivation properties and kept them within standard limits.