فصلنامه تحقیقات مهندسی کشاورزی
سال سیزدهم شماره 2 (تابستان 1391)

Decreasing water resources has made optimum water allocation in agriculture essential. Planning optimum irrigation and crop production function considering accessible water and growing stage is an efficient approach to increase water productivity. Studies have applied this approach to maximize crop production using the FAO crop production method introduced in 1979. However, the FAO introduced a new method in 2003 that has been rarely studied. The objective of this study is to compare the performance of the two FAO methods in the Zayandh Rud irrigation system using climate information from the 1998 drought in the region. Wheat, barley, sugar beets and potatoes, the region’s main crops, are selected and their production function and temporal pattern of optimum irrigation water by growing stage (10 days of irrigation) are compared. The results show that the new FAO method estimates lower crop yield under water stress; however, the temporal pattern of irrigation depth is smoother and more uniform during the crop growing stages.

Because it is not possible to recognize the mechanism of cantilever failure in field studies, this type of common failure in riverbanks is investigated in the laboratory. For this purpose, two samples of susceptible soil that forms an overhanging block in riverbanks are used for physical model tests to determine their physical, chemical and mechanical characteristics. Soil blocks of different densities were formed and then undermined by hand at specific depths over specific time increments and the stability of the overhanging block were assessed at each step. The results showed that, under these laboratory study conditions, the dominant failure mechanism is toppling. This finding is in accordance with the overhanging failure pattern in the Kordan Riverbanks. It was also found that the failure mechanism in cohesive soil is progressive and accompanied by tension crack development. In Loess material, the failure mechanism is momentary and no deformations in the upper part of the soil block are observed.

This study investigated the effect of sowing date and limited water allocation management for single irrigation on the grain yield of rainfed barley. The experiment was a split-split plot arranged in a randomized complete block design with three replications from 2004 to 2006 at the main station of the Dryland Agricultural Research Institute at Maragheh. The treatments comprised three sowing dates (early, normal, late) and Yesevi-93 (Abidar), and Dayton (URB79-7) barley varieties. The single irrigation allocations tested were rainfed, planting time irrigation (50 mm and 100 mm), and spring irrigation (50% and 100% depletion of available water). Grain, straw and biomass yields were measured. Barley production function was estimated for total water used (sum of precipitation and irrigation water). Generally, there was a linear function between water use and yield and the effectiveness of the amount and time water allocation was evident. Results showed that single irrigation at planting time and limited single irrigation (50% depletion of available water at root zone) at spring time (during heading to flowering stage) had significant effects on yield and water use efficiency. The average grain yield for single irrigation at planting time (3794 kg.ha-1) was about 300% more than the average for rainfed (1170 kg.ha-1). Single irrigation at planting time caused early crop establishment for autumn and relatively early maturity, which reduced the growing period. The grain yield for spring single irrigation was about 1000 kg.ha-1 more than the average rainfed condition. Spring single irrigation improved soil water content and increased yield and yield components (especially thousand kernel wt.). Thus, wheat production can be substantially and consistently increased under cooperative management of limited single irrigation and agronomic management.

Bananas are climacteric fruits and controlling ripening is effective in reducing loss. This experiment studied the effect of packaging (plastic bag, edible wax and plastic bag, plastic bag and 2 or 4 g/kg potassium permanganate) over 5 weeks of cold storage on the quality and characteristics of Cavendish cultivar bananas. The samples were removed from storage at 8, 16, 24, 32 and 40 days and fruit maturity (pH, hardness of fruit pulp, percent tannin, pentoses, amount of phenol, total carbohydrates) were measured. The experiment was a factorial completely randomized design with four replications (each with four bananas). Changes in ripening measured for control bananas stored in an open area showed total soluble solids (TSS), pentoses and glucose increased and pH, hardness of fruit pulp, percent of tannin, and amount of phenol decreased. The use of wax treatment and plastic bags or wax and plastic bag with potassium permanganate decreased the ripening process significantly. Wax and plastic bags and 4 g potassium permanganate was the most effective treatment to prevent an increase in TSS, pentoses and glucose and decrease pH, hardness of fruit pulp, percent of tannin, and amount of phenol. The use of potassium permanganate, plastic bags and wax was effective in preventing the effects of ethylenes and delay ripening of bananas.

This research was conducted to determine the best temperature for storing different melon cultivars (ghasry, khaghany, tashkandy) and the best concentration and treatment length for immersion in an emulsion of sunflower oil and sodium bicarbonate. After harvest, precooling and sorting, the melons were treated with an emulsion of sunflower oil (3%, 5%) and sodium 2% sodium bicarbonate for 5 or 10 min. All treatments and the control were placed in cold storage at 1, 5, 10, 18, or 25 °C at 90%-95% relative humidity for 45 days. Quantitative and qualitative characteristics of melons (decay, weight loss, chilling injury, total soluble solids, flesh firmness, sugar content) were measured immediately after harvest and at 15 day intervals. Panel testing was done at the end of storage. The results showed that immersion in 3% sunflower oil and 2% sodium bicarbonate emulsion for 10 min, 5% sunflower oil emulsion and 2% sodium bicarbonate for 5 min, and 5% sunflower oil and 2% sodium bicarbonate for 10 min maintained the quantitative and qualitative characteristics of khaghany cultivar followed by tashkandi and ghasri cultivars. Temperatures of 1 and 5 °C were most suitable for preserving khaghany melons and 10 °C was best for tashkandy and ghasry cultivars.

This study assessed the effect of asesulfame K on the stability of aspartame in diet cola. Since acesulfame K is resistant to high temperatures, the effect of a blend of two sweeteners on its thermal resistance in diet cola was also studied. A cola containing two sweeteners (1:1 weight ratio) was prepared and, after quality control testing, was stored at temperatures of 4, 25 and 40 °C for 6 months. The concentration of aspartame remaining was measured every 15 days using high performance liquid chromatography. Statistical results showed better stability of aspartame in cola containing acesulfame K. The kinetic equations of aspartame decomposition represented a first order reaction; aspartame halflife results also confirmed this result. The amount of activation energy was greater in cola without acesulfame K and indicated the greater effect of temperature on aspartame decomposition in this sample.

Individual daily requirements recommend 25-35 g dietary fiber to maintain overall health and aid digestion. Dietary fiber exists in fruits and vegetables, but can also be obtained by adding wheat bran to bread. Wheat bran, however, contains high levels of phytic acid that is known to chelate iron, calcium, zinc, and magnesium and form complex phytic acid cations that reduce their bioavailability in food. If the phytic acid content of wheat bran can be reduced, it can be a rich source of fiber with no harmful effects. In this study, soaking wheat bran in water, and adding sourdough or malt powder were tested for their effects on reducing phytic acid. Results showed that all treatments significantly reduced phytic acid in dough and bread over the control. The lowest and highest phytic acid contents were for 4% malt powder and the control, respectively. The use of 4% malt powder, however, damaged bread quality, thus, 10% sourdough and 2% malt powder were selected as the best treatments.

Cumin is an annual plant suitable for cultivation in dry and semi-dry lands of Iran. It is harvested in two periods to prevent seed loss. Manual harvesting either by hand or using a scythe forms the initial stage. After drying and threshing, in the final stage, the seeds are manually sieved to be cleaned and separated from foreign material. This harvesting method is time-consuming and labor intensive and causes high loss, decreasing quality and increasing seed pollution. A combine harvester was used to study the function of effective factors on the separation and cleaning of cumin seeds after threshing. The effect of independent variables (type of straw walker, wind speed, sieve blade angle, sieve angle) on dependent parameters (percent of seed loss by weight from straw walker, from cleaner system, percent of straw by weight in seed hopper) was investigated using a randomized complete block design. As the size and moisture content of cumin seed increased, terminal velocity increased. The results showed that wind speed, sieve blade angle and sieve angle had significant effects (P < 0.01) on percent of seed loss by weight in the cleaner system and percent of straw by weight in the seed hopper. The percent of seed loss in the straw walker was also affected by the type of straw walker used.