JOURNAL OF AGRICULTURAL SCIENCE AND SUSTAINABLE PRODUCTION
Year:2006 | Volume:16 | Issue:3|Papers Count:29

Currently available numerical algorithms employed in unsteady flow models usually present some difficulties while facing flow discontinuity, unless they were based on simplified form of the governing equations, which yield approximate solutions. Field observations and experimental data could provide a sound base for proposing simple and robust solutions to be directly used in the numerical models or to improve the current algorithms. In order to study the unsteady transcritical flow and to develop such relationships, an experimental setup was constructed and used. In this setup the phenomenon of moving hydraulic jumps, which is regarded as an unsteady transcritical flow, were developed and data were recorded under variety of circumstances. According to the compiled data, simple yet practical and time independent relationships were obtained. They were employed in determining the downstream characteristics of the transcritical flow, downstream boundary conditions and the water surface profile at any given moment associated with the employed upstream boundary condition. These relationships were mainly based on the discharge data of upstream boundary, and the supercritical flow conditions. Since the data employed in this study cover very wide range of hydrograph shapes and different longitudinal slopes, they provide reliable and applicable results.

This field experiment was conducted in order to reduce undesirable flooding effects due to heavy and continuous rainfalls. Drainage and nitrogen fertilizer effects on rapeseed yield in the paddy field at the north of Iran (Rice Research Institute, Rasht) were investigated. A split-plot design arranged in randomized complete blocks with three replications was employed using Hyola 308. Factors included three drainage levels (1- no drain, 2- surface drain with 2m spacing and average depth 15cm, 3- surface drain with 4m spacing and average depth of 15cm crossing with 1m spaced lateral ditches which were 7cm in depth) and four nitrogen fertilizer levels (0, 150, 200 and 250 kg/ha N that was splitted as 1/3, 1/3, 1/3). The results indicated that although after each rain, drains with 2 and 4 m spacing could not reduce soil moisture to the field capacity level, but increased grain yield to 97.8% and 94.3%, respectively due to improvement of soil condition. Meanwhile reduction in the soil moisture was about 3% and 4.6% and decrease in water table was approximately 30% and 21% with respect to no drain condition. On the other hand, using only minimum of 150 kg/ha N can reduce undesirable flooding effects and increases grain yield up to 67%. In general, considering all the phenomena involved in the paddy fields (environmental problems, soil conditions, operational suitability & costs) surface drain with 4m spacing along with nitrogen fertilizer of at least 150 kg/ha N can be suggested.

Deficit irrigation technique is a type of irrigation management that leads to save water without damaging plant and economic loss in yield. This experiment was conducted during 2003-2004 in order to study the effects of deficit irrigation on five advanced barley genotypes at Kaboutarabad Station of Esfahan, Iran. Experimental design was a randomized complete block with split-plot arrangement. The main-plots comprised five irrigation treatments as tradition irrigation in the area (five irrigations per season) as control, 10, 20, and 30 percent reductions in seasonal irrigation depth relative to the control. The sub-plots were five advanced barley genotypes as Karoonx Kavir, Valfajre, M-79-4, M-79-7 and M-79-15. Analysis of variance showed that deficit irrigation had significant effects (P<0.05) on the number of days to spike emergence, numbers of spikes per unit area, grain yield and harvest index. Deficit irrigation had no significant effect on plant height, peduncle length and spike length. All of the measured characters were significantly (p<0.01) influenced by the type of genotype. Highest grain yield (7392.9 kg/ha) was produced by M-79-4 line. Water use efficiency of this line was 1.47 Kg/m3. The 20% deficit irrigation treatment produced the highest water use efficiency (1.35 Kg/m3).

The North Atlantic Oscillations (NAO) is the dominant pattern of atmospheric circulation variability in the extra tropical division of Northern Hemisphere and it is a major controlling factor of basic climatic elements such as temperature and precipitation, which have large socioeconomic impacts on energy, agriculture, industry, traffic and health divisions. In this study the data relating to NAO and winter precipitations were studied for East Azerbaijan Province in a time period of 43 years (1960-2002) aiming at the calculation of coefficient of correlation and determination of wet years and droughts. The main methodologies being used in this research were the regression (linear, power, exponential, logarithmic and polynomial), Pearson and Spearman correlation coefficients, and trend components for the analysis of the winter precipitation and NAO. Negative correlations (specially in intensive wet winter and winter droughts) obtained between winter precipitation and NAO index in Tabriz, Jolfa, Ahar and Sarab stations. This is an indicative of the increase of precipitation and occurrence of wet periods during the negative NAO phases, and on the contrary, the precipitation reduction and occurrence of droughts during the positive NAO phases.

Despite the importance of agricultural research in Iranian research policy, its income redistributional effects have not been studied yet. The income distributional impact of Iranian agricultural research policy is evaluated using the economic surplus approach and using sugarbeet as the case. The results indicated that 212.5 percent of the potential gains from sugarbeet R & D go to producers and the remaining -112.5 percent to consumers. It means that not only all the gains are received by producers but some income is transferred from consumers to producers as well. Urban settlers incur -113 percent of the gains and beet growers receive more than 100 percent of the producers' benefits. It is concluded that sugarbeet research policy is very efficient from equity (redistribution of income to the poor) perspective.

In this research, the trend and direction of technical change in livestock industry of Iran was studied using duality theory in costs. The approach given in the duality theory was found useful in estimating the input demand structure under changing input prices and technology conditions. Applying SURE method, a translog cost function with the cost share equations estimated, using panel data from 24 provinces of Iran for the period of 1990-2000. The results showed that the rate of technical change was -1.37 percent over the mentioned time period, which means in the study period the rate of cost change of production units have been decreased. In addition, technical change was indicated feed-using, labor-saving and energy-saving biases.

In the present study land suitability evaluation (qualitative classification) was carried out for wheat, barley, safflower, bean, soybean and potato production in an area of 385 ha at Yakhfarvazan region of Ahar in East Azarbaijan, Iran. Soil data was prepared by studding 22 soil profiles and agurs and the regional information, including climatic and agronomic data were collected. Simple limitation method, limitation method regarding number and intensity, and parametric methods (Storie and Square Root) were employed and land suitability classes were determined for 18 land units. In simple limitation and limitation method regarding number and intensity almost 42.4% of area are moderately suitable (S2), 37.2% are marginally suitable (S2) and 20.4% are unsuitable (N2) for wheat and barley production. Thirteen percent of the area is moderately suitable, 44.2% is marginally suitable and 42.8% is unsuitable for safflower. For bean production 18.8% of the area is moderately suitable, 17.5% is marginally suitable and 63.7% is unsitable whereas 13% is moderately suitable, 36.7% is marginally suitable, and 50.3% is actually unsuitable for soybean, and finally 31% of the area is moderately suitable, 16.7% is marginally suitable, 9.5% is actually unsuitable and potentially suitable, and 42.8% is unsuitable for potato production. In Storie method almost 55.5% of the area is marginally suitable and 44.5% is unsuitable for wheat. For barley, 9.7% is moderately suitable, 56.3% is marginally suitable, and 34% is unsuitable. For safflower, 22.7% is marginally suitable and 77.3% is unsuitable. For bean, 18.8% is marginally suitable, and 81.2% is unsuitable. For soyban, 14.9% is marginally suitable and 85.1% is unsuitable and also for potato, 16.6% is marginally suitable and 83.4% is unsuitable. In square root method, almost 24.4% of the area is S2, 55.2% is S3, and 20.4% is N for wheat, 42.4% is S2, 37.2% is S3, and 20.4% is N for barley, 10.8% is S2,46.4% is S3, and 42.8% is N for safflower, 12.7% is S2,6.1% is S3,and 81.2% is N for bean, 10.8% is S2, 11.9% is S3, and 77.3% is N for soybean, and for potato, 4.7% is S2, 26.3% is S3, and 69% is N. Based on the results (especially those from the square root method), the priority of the studied area turned to be barley and wheat (first) bean, safflower, soybean (second), and potato (third). Among the methods, square root was more realistic in the present study.

In order to assess the growth indices of three winter rapeseed cultivars at different seeding dates, a field experiment was conducted at the Research Station of Faculty of Agriculture, University of Tabriz, in 1996. The research was performed as factorial, based on randomized complete block design with three replications. Factors include three sowing dates (Sep. 18, Oct. 3, and Oct. 18) and three cultivars of winter rapeseed (Blinda, Cobra and Quinta). Results revealed that leaf area index (LAI), total dry matter (TDM) crop growth rate (CGR) and relative growth rate (RGR) of rapeseed cultivars decreased, as sowing date delayed. Growth indices were significantly different among rapeseed cultivars. These differences were greater after anthesis. LAI, TDM, CGR and RGR of Blinda were higher than Cobra and Quinta, leading to higher grain yield for Blinda.

For identifying genotypes with high drought stress tolerance and high yield potential, 24 advanced new bread wheat genotypes were evalueted in a randomized complete block design with three replications under three irrigation regims, such as non-stress (Yp), pre-anthesis drought stress (Ys2) and post-anthesis drought stress (Ys1) in Ardabil Agricultural Research Station during three years 1997-98, 1998-99 and 1999-2000. Results showed that drought stress intesity (SI) under parenthesis stress (SI=0.33) was higher than post-anthesis stress (SI=0.26). The grain yield of genotypes under pre-anthesis drought stress was significantly less than the yield under non-stress and post-anthesis drought stress conditions. Grain yield under pre-anthesis drought stress was significantly and positively correlated with grain weight/plant (r =0.58**).Grain yield of genotypes on the basis of mean productivity (MP), geometric mean productivity (GMP), drought tolerance (TOL), stress susceptibility (SSI) and stress tolerance (STI) indices were evaluated. Selection based on TOL and SSI identified the tolerant genotypes having low yield potential while selection based on MP, GMP and STI identified genotypes with high yield and high drought stress tolerance. MP, GMP and STI indices were highly and positively correlated with Yp, YS1 and YS2, but TOL and SSI indices were significantly and non-significantly correlated with Yp, respectively. However they were correlated negatively with YS1 and YS2 On the basis of three-dimensional plot, genotypes were classified into four groups (A, B, C and D) and consequently genotypes 4, 13, 14, 15 and 21 were identified as tolerant genotypes with high yield. Heritabilities of studied characters such as peduncle length, sterile spikelets /spike, plant height and 1000 grain weight were high. Measuring cytoplasmic membrane damage and membrane stability at booting and heading stages under preanthesis drought stress showed genotypes no 1, 13 and 21 had more stable membrane and less cytoplasmic membrane damage and were identified as desirable genotypes. The stability of membrane and membrane damage were heritable in heading stage but not in booting stage.

Effect of irrigation regimes and plant densities on water use efficiency (WUE) of three safflower cultivars was investigated at the Research Station, Faculty of Agriculture ,University of Tabriz using a field experiment arranged as split plot factorial based on randomized complete block design with three replications. Four irrigation regimes based on phonological stages, I1=irrigation up to R1, I2=irrigation up to R2, 13=irrigation up to R3 stages, and I0=control, and three varieties, V1=L.R.V 51/51, V2=Zarghan 279, and V3=Varamin 295 with two densities (D1=20 and D2=40 plants/m2) comprised the experimental factors. Analysis of variance showed that the effect of irrigation regimes, cultivars and plant densities on WUE for grain yield was statistically significant. Mean comparison of irrigation regimes showed that the first level of irrigation placed in second group and all the other placed in the first group. I3 level with 4172 m3/ha water use and with more WUE compared with control identified as the best level. Zarghan and L.R.V with the highest grain yield placed in the first group followed by Varamin. The highest WUE belonged to D2. WUE for biological yield was high under irrigation regimes I1, h. D2 showed higher WUE for biological yield than D1. Interaction effect of irrigation regimes x cultivar x density was significant statistically, with respect to WUE for petal yield. L.R.V under 13 and D2 with 0.21 kg petal per m3 water, showed the highest WUE for petal yield. The results of this research showed that increase in plant density, increased WUE markedly, because of increasing grain yield, biomass and petal yield. Meanwhile, I3 level showed an acceptable yield and WUE in this experiment.

In order to evaluate growth habit of 151 available durum wheat varieties and lines in Maragheh Agricultural Research Station yield trials and determine correlation among some agronomic traits and growth habit, this study was conducted during three growing seasons (1998-2001).The method was the same as is usually used in the International Wheat Research Centers to determine the growth habit of wheat genotypes. Means of agronomic traits (days from planting to spike emergence and maturity, grain filling period, plant height, 1000 kernel weight and grain yield) from yield trials were used to study their relationship with each other. Results showed that 51% of the genotypes were spring types the most frequent growth habit among studied genotypes. Percent of winter and facultative genotypes were 33% and 16% respectively. Comparison of means for grain yield showed that there were highly significant differences (p£0.01) among different growth habits and the highest grain yield (1.200 t/ha) belonged to spring types. Correlation between growth habit and plant height was negative and significant (r = -0.16). Correlations between grain yield and days to spike emergence, days to maturity, grain filling period and plant height were 0.51, 0.65, 0.56, and 0.47 respectively, which were highly significant. For high yielding genotypes in Maragheh and similar climatological regions selection for traits such as days to spike emergence, days to maturity, grain filling period, and plant height are recommended.

Rice blast, caused by Magnaporthe grisea Hebert (Barr.), is often an important constraint in rice production areas. Attempts to utilize single resistance genes to control the blast disease have met with little permanent success. Accordingly, other breeding strategies are being considered, including the use of slow-blasting or quantitative resistance that reduces the disease severity. This study was undertaken to determine i) reaction of rice genotypes from Iran to blast pathogen isolates and field population of the pathogen, ii) evaluation of components of resistance and rates of disease development (slow-blasting), iii) the area under disease progress curves, AUDPC, of the rice cultivars used. Experiments were set as a randomized complete block design (RCBD), with three replicates in both greenhouse and field tests in Rice Research Institute of Iran in Rasht in 2003. Results showed that the reaction of 30 most popular rice cultivars were differentially significant to different blast isolates. Cultivar x isolate interaction was also significant. In the upland nursery, disease progress varied greatly between the cultivars. The results suggest the presence of specific major gene(s) for resistance in rice and virulence gene(s) in pathogen.

The effect of process temperature (T) at three levels (30, 40 & 50°C) on dynamic behavior of permeates flux (Jp), total hydraulic resistance (RT), and milk solutes rejection (protein, Rp; fat, RF; lactose, RL; minerals, RM and total solids, RTs) was studied. Experiments were carried out using a pilot plant UF membrane system equipped with a spiral wound module and a polysulfoneamide membrane. A three-stage strategy based on a resistance-in-series model (boundary layer-adsorption) was used to determine the different hydraulic resistances. The results showed that Jp decreases greatly with increasing process time (t), both initial flux and pseudo steady state flux increase only between 30-40°C, and further increasing of T had no effect on fluxes. RT increased during operation at all levels of T. Also increasing T led to increasing both RT and irreversible fouling resistance, but reversible fouling resistance decreased and membrane hydraulic resistance did not change. The milk solutes rejection results showed that the Rp and RF at each value of T were constant with t, whereas RL, RM and RTS increased significantly with t at the corresponding T. Meanwhile increasing T had no significant effect on the rejection of each solute at the end of operation.

An experiment was conducted to determine the effects of inclusion levels of 0 (control), 5, 10, and 15 % dried tomato pomace (TP) on performance and egg quality of laying hens. This experiment was arranged in a completely randomized design with 4 treatments and 12 replicates on 288 laying hens from a commercial strain (Hy-line W36) at 27 - 37 weeks of age. Results indicated that the inclusion levels of TP affected the egg production, egg mass and feed conversion ratio (P<0.05). There was a quadratic response of laying hens to concentration of the TP. Inclusion level of TP up to 10% resulted in more egg mass and egg production than control diet. Inclusion of the TP at 15% decreased egg production and egg mass, but increased feed conversion ratio as compared to the control diet. Feed consumption, body weight, egg weight, haugh unit, egg shell thickness, egg shell weight and yolk color were not significantly affected by the concentration of the TP. It was concluded that TP can be used as an alternative feedstuff in laying hen diets at inclusion levels up to 10% without negative effects on performance and egg quality.

An experiment was conducted to evaluate the response of broiler chickens to different levels of natural zeolite. The experimental design was arranged as randomized complete blocks in a 4x2 factorial arrangement of treatments. Four levels of natural zeolite (0, 1.5, 3 and 4.5%) were compared in both male and female chickens. Five replicates of 10 birds were assigned to each treatment. Birds received the experimental diets at free access from 1 to 42 days of age. The results showed that birds on diets with 3 and 4.5% zeolite had heavier final body weight (5% more than the control). The highest weight gain during the experiment was attained by the chickens received 4.5% zeolite. There were no significant differences with respect to feed intake and feed conversion ratio throughout the experiment. However, the main effect of sex was significant in terms of feed intake during the growing period and end of the experiment so that males and females consumed 3408.1 and 3202.3g, respectively (P<0.05). Dietary treatments did not significantly affect carcass, breast and thigh yields.

A total of 3310 first lactation records of Iranian Holsteins cows, which were collected between 1994-1999 were used to estimate genetic parameters for 19 type traits as well as herd life based on REML methodology using animal model. The highest heritability estimates were found for stature (0.36±0.07) and size (0.35±0.08) while the lowest heritability estimate was found for foot angle (0.02±0.003) Genetic correlation between udder depth and teat length was the highest (0.90) while the lowest genetic correlation was observed between body depth and pin set (0.01). Among type traits and in terms of absolute value, herd life had highest and lowest genetic correlations with pin width (-0.90) and rump width (-0.03), respectively. The result of the present research indicate that herd life is more influenced by udder rather than bodily traits suggesting longer herd life in Iranian Holsteins could be expected where direct selection is practiced for udder traits.

Thirty-six culled male Lori- Bakhtiari lambs, with the average body weight of 53.2±6.15 kg and 270±20 days of age were used in order to study fattening performance and carcass characteristics by feeding of Urea Treated Rice Straw (UTRS) for alfalfa hay replacement. Animals were assigned as a completely randomized design using three diets with 0, 50, and 100% UTRS, respectively, and were substituted on dry weight basis. The diets contained 2.4 Mcal/kg DM metabolizable energy, 13% crude protein for fattening period lasted 80 days after adaptation. The diets fed to animals on the whole meal and adlib consumed at three times a day (6.00, 12.00, 18.00). The means of daily food use was recorded. At the end of the experiment, four lambs from each group were randomly slaughtered for evaluation of physical carcass characteristic. The mean average daily gain for treatments 1, 2 and 3 were 163,143 and 112 (±17) g, respectively, and the difference between treatment 1 and 3 was significant (P<0.05). Dry matter feed intake for the treatments 1, 2, and 3 were 1.9, 1.75 and 1.48 kg/day, respectively, but the differences were only significant between treatment 3 and treatments 1 and 2. The means feed conversion for treatments 1, 2 and 3 were 12.5, 14.8 and 14 (±1.9), respectively, but the differences were not significant. The treatments had no significant effect on the means dressing percentage, meat, bone, and subcutaneous fat and tail fat weight. It can be concluded that use and feeding of UTRS up to 50% of alfalfa in the diet of fattening lambs can be useful.

An experiment was conducted to study the effects of b-glucanase supplementation on the performance and gastrointestinal tract size of chicks fed barley based diets and growth stimulator antibiotices up to 42 days. In this study 400 day-old Ross male chicks were used (each pen had 25 chicks) in a completely randomized design with four treatments: 1- control (barley based diet), 2- control+ enzyme supplementation (500U avizyme), 3- contro1+ antiobiotic (virginiamycin, 20 ppm), 4- control+ enzyme supplementation (500U avizyme) plus antiobiotic (20 ppm) and four replicates. The traits measured were feed intake, feed conversion ratio, body weight gain, and gut development. Inclusion of enzyme significantly increased body weight (P< 0.05). There were no significant differences between treatments for feed intake. Feed conversion ratio was significantly impacted by adding of enzyme supplementation in treatments 2 and 4 (2.13 and 2.1 versus 2.27).Antibiotic supplementation had no significant effect on body weight, feed intake and gastrointestinal tract development. The addition of barley in the diet decreased the performance due to presence of nonstarch polysaccharides and enzyme significantly decreased relative weight and length of juojenum and ileum (P<0.05), which shows adaptation process in broilers exposed to higher level of barley.

This survey was done for determining of helminthes fauna of small ruminant's digestive tract in East Azarbaijan province. Four-hundred alimentary tracts and livers of small ruminants (sheep and goat) were collected from eight slaughterhouses in the province and were studied in parasitology laboratory of faculty of veterinary medicine in University of Tabriz. Rumens and reticula were free from helminths. Other parts had at least one type of worms. In this study 15 genus and 21 species of helminthes were recognized. Number and variety of nematodes were more than trematodes and cestodes. In Ahar, population of helminthes in digestive system of small ruminants was higher and in Azar-Shahr was lower than others. Gongylonema pulcorum was observed only in esophagus. Ostertagia occidentalis, Nematodirus oriatianus, Chabertia ovina, and Dicrocoelim dendriticum were common in abomasums, small intestine, large intestine and liver, respectively. Comparison of the results of this survey with recent studies in this province and other provinces indicated that helminthes prevalence have been reducing, probably because of strategic deworming in recent years.

This research was undertaken to study maternal effects on five production and reproduction traits using records collected over six generations from a selected breeder flock of native hens kept at a breeding center in Fars province, Iran. The traits were body weight at 12 weeks of age (BW12), body weight at sexual maturity (MBW), age at sexual maturity (ASM), egg number up to 32 weeks of age (EN) and egg weight at 32 weeks of age (EW). Variance components and heritabilities were estimated by the Henderson's method 3 using paternal half-sib and full-sib models and restricted maximum likelihood (REML) procedure under an animal model (AM). Heritability estimates for BW12, MBW, ASM, EN, and EW were 0.237, 0.243, 0.348, 0.258, and 0.338, respectively, based on paternal half sibs, 0.436, 0.329, 0.363, 0.172 and 0.381, respectively based on full sibs, and 0.374, 0.341, 0.352, 0.186, and 0.389, respectively, based on animal model. Comparison of the results from paternal half-sib correlation with those of full-sib correlation and animal model for body weight traits indicated that these traits may be affected by maternal effects.

Tea root lesion nematode, Pratylenchus loosi Loof, 1960, is one of the most destructive pests of tea shrubs in all over of tea growing areas such as north of Iran. In this study, total soluble protein profiles from 15 populations of tea root lesion nematode, P. loosi from different geographical areas of Guilan province were investigated by SDS-PAGE method. Esterase isozyme phenotypes of the populations were also studied by native PAGE method. Evaluating total soluble protein profiles of studied populations showed similar profiles among all studied populations. Study of esterase phenotype of these populations resulted in three b esterase phenotypes, some of them had R¦=6.2 (phenotype A), other had R¦= 10.4 (phenotype B) and another group had both forms of phenotypes (phenotype AB). Also severity of gene expression among the phenotypes A, B and AB were detected as 1, 1 and 1:1, respectively.

The susceptibility of summer eggs and adult females of European red mite to propargite EC 57%, hexythiazox EC 10%, and neem oil was evaluated during 2000 - 2001. Apple leaves with eggs were slid dipped in 7 concentrations of the each compound and water treatment as check for five seconds. The adult females were transferred to the treated leaves. In preliminary experiments we used 7 concentrations of each treatment and a check treatment (water). In complementary experiments we used logarithmic rates of the compounds according to the standard procedure. The estimated LC50 values for hexythiazox, neem oil and propargite for eggs were 125, 742 and 155x106 p.p.m., respectively. The estimates for adult females were 464x103, 708 and 593 p.p.m. in the same order. The data were analyzed by probit procedure. The neem oil could control the European red mite at an appropriate rate. This concentration of oil deserves to be considered as a potential compound to control Panonychus ulmi (Koch) under field conditions.

On the basis of the investigations in different parts of the world, rapeseed yield content (%) and seed loss (%) during harvesting operation are related to harvesting time and methods as well as seed moisture content. Evaluating and comparing of different types of harvesting systems and machines were the main objectives of this research. These methods from the view point of their impacts on seed loss, crop yield, oil content, total cost, effective field capacity and net benefit were studied. A randomized complete block design with four replications was used and the data was analysed. Treatments being direct harvesting with grain combine: Double stage harvesting with conventional mover followed by threshing: Double stage harvesting with high clearance mover followed by threshing .Hand cutting followed by threshing. The results indicated that combine harvesting caused maximum seed loss, therefore, it can be concluded that on time harvesting can reduce seed loss. Among these harvesting methods, direct combining had the highest effective field capacity and the lowest cost. The lowest effective field capacity and the highest cost belonged to hand cutting .According to the results, there was no significant difference between harvesting methods from the view point of net benefit. Therefore, any of the above harvesting methods best fitted to our farming system can be selected.

Since variations in repair and maintenance costs are excessively dependent on current conditions, so a standard relationship cannot be suggested for these variables, for example in the case of depreciation costs. But estimation of these costs at acceptable level can be made by fitting a mathematical model based on previous data. For fitting relationships between accumulated hours of service and accumulated costs of repair and maintenance, 42 two-wheel drive tractors in four models: Massey Ferguson 285, John Deere 3140, John Deere 4450, and Fait, working actively at Kesht & Sanat Astan Ghodse Razavi farms, were chosen. Carrying out regression analysis and considering the significance of regression coefficients, exponential model for the first part of useful life and quadratic model for remaining life period is suggested for Massey Fergusen 285 and John Deere 3140 tractors. Power based and exponential models were recommended for John Deere 4450 and Fiat tractors, respectively. Finally, for all two wheel tractors the power and quadratic model were considered as the most desirable for the first period of life and remaining life period, respectively. Comparisons of fitted curves among tractor models indicated that repair and maintenance costs as a percent of purchase price for four tractor models were in the ascending order of John Deer 4450, John Deer 3140, Massey Ferguson 285, and Fiat, respectively. This result may be related to the design quality and manufacturing procedures which can affect on reliability of tractors.

In order to study the assessment of energy consumption of tillage tools in corn forage production six tillage systems consisted of three primary (moldboard, disk, and chisel plows) and two secondary(disk harrow and two times field cultivator) tillage tools were studied in a factorial experiment based on randomized complete block design with four replications. The results showed that treatment A (chisel plow + disk harrow) with 2164.32 Mj/ha and treatment F (disk plow + 2 times field cultivator) with 1268.31 Mj/ha had the lowest and highest energy consumption, respectively. The total percentage of energy used by fuel, machine and labor ranked as 88.46%, 10.98% and 0.56%, respectively. The energy conservation by chisel plow was 15 and 20.5 percent more than moldboard and disk plow, and in the case of disk harrow energy conservation was 24% more than two times of field cultivator. In conclusion the performance of treatment A in this study with the lowest energy consumption and highest coin forage energy ratio was better than the other treatments.