نشریه ماشین های کشاورزی
سال سوم شماره 1 (پیاپی 5، نیمسال اول 1392)

Soil compaction can occur as a result of a number of factors. One of the most important factors is soil response to pressures imposed by wheels and soil engaging tools. This research investigated the effect of tyre load and inflation pressure on soil compaction-related factors. These factors include rut width, rut depth, cone index and horizontal force in different layers of soil profile. In this research a stiff carcass tyre has been used and a soil compaction profile sensor in controlled soil bin laboratory conditions. This sensor consisted of eight flaps, each equipped with strain gauges, installed on a subsoiler leg face with working depth of 45 cm. Studies were conducted using a factorial experiment at two levels of axle load of 6.3 kN and 23.9 kN and three levels of inflation pressure of 324 kPa, 524 kPa and 724 kPa with three replications in a randomized complete design. Duncan test and F test were applied to compare the means of pressure and axle load, respectively. The soil compaction profile sensor measured soil compaction at different layers from soil surface to 45 cm depth at 5 cm interval. The results of experiments indicated that vertical load significantly affected the horizontal force at different tyre inflation pressures on the soil profile. The tyre inflation pressure exhibited greater effects on shallow depths than those of higher depths. The amount of rut width, rut depth and cone index increased with an increase in vertical load. Increasing of the inflation pressure decreased rut width and increased rut depth and cone index.

Agricultural sector experiences the application of automated systems since two decades ago. These systems are applied to harvest fruits in agriculture. Computer vision is one of the technologies that are most widely used in food industries and agriculture. In this paper, an automated system based on computer vision for harvesting greenhouse tomatoes is presented. A CCD camera takes images from workspace and tomatoes with over 50 percent ripeness are detected through an image processing algorithm. In this research three color spaces including RGB, HSI and YCbCr and three algorithms including threshold recognition, curvature of the image and red/green ratio were used in order to identify the ripe tomatoes from background under natural illumination. The average error of threshold recognition, red/green ratio and curvature of the image algorithms were 11.82%, 10.03% and 7.95% in HSI, RGB and YCbCr color spaces, respectively. Therefore, the YCbCr color space and curvature of the image algorithm were identified as the most suitable for recognizing fruits under natural illumination condition.

The underground temperature at a depth of about three to four meters is almost constant during the year. As a result in summer the underground is cooler than the ambient temperature. This potential is considered for greenhouse cooling by using an Earth-to-Air Heat Exchanger (EAHE). In this research the effects of two parameters were investigated: a) the area of greenhouse in three levels of 9, 18, 27 m2 and b) the percent of vegetation coverage inside the greenhouse in three levels of 0%, 50%, 100% on the performance of EAHE. The experimental design was factorial experiment in a randomized complete block design. The parameters of greenhouse’s inside temperature, thermal energy exchange and coefficient of performance (COP) were considered in cooling mode. As one of the remarkable results it was observed that the closed loop utilization of the system was infeasible in cooling mode. This was mainly due to the occurrence of vapor distillation inside the underground pipes and hence the blockages of the air flow. Also the effect of area and the percent of vegetation coverage were significant on the performance of EAHE. The highest average temperature difference between the temperature of testimonial greenhouse and the temperature of greenhouse was observed in treatment of 100% vegetation coverage and 9 m2 floor area which was measured as 9.6°C. The least average temperature difference in the treatment without vegetation coverage and 27 m2 floor area was measured as 5.2 °C. Considering thermal energy exchange in cooling greenhouse with open loop, the best treatment determined for EAHE in this research was the one with 9 m2 floor area and 100% of vegetation coverage.

This study was carried out to evaluate the effects of tillage practices (with different depths) on soil penetration resistance, technical parameters and grain yield of wheat crop. The experiment was conducted as a randomized complete block design with three replications for two years. Treatments included: moldboard plow fallowed by two passes of disc harrow and leveler (CT), two passes of disc harrow plus leveler (RT), subsoiler fallowed by two passes of disc harrow and leveler (S1D) and subsoiler fallowed by rotivator (S1R). The results showed that soil compaction and penetration resistance increased at the end of growth stages because of irrigation operations and cohesion force of soil particles. However due to increasing of cumulative infiltration, it can be concluded that subsoiler caused the formation of micro cracks in different depths of soil. From technical indices viewpoint comparing to CT treatment, S1D and S1R treatments saved fuel consumption up to 2.2 and 10.44 lit ha 1 and tillage operation time up to 0.58 and 1.54 h ha-1, respectively. The result of grain yield assessment showed an increase of 8.5% in grain yield after replacing moldboard plow with annual subsoiling. Subsoiling has advantages such as, good technical indices, elimination of preplanting irrigation and fewer operations in planting time. Finally, subsoiling increased grain yield by 22% as compared to reduced tillage practice

A three-year field experiment (2004-2007) was conducted on a silty clay loam soil at Tajarak Research Station of Hamedan to determine proper grain drill for wheat in Hamedan dryland areas. In this study, three grain drills including: Hamedani Barzegar; Sahalan Kesht; and Kesht Gostar with wheat seed broadcasting and disking were used. The experiment was a randomized complete block design with four replications. In laboratory, the precision of metering device and the amount of seed damage by metering mechanism were measured. At the end of growth season (harvesting time), crop yield and the associated parameters (spike per m2, number of grain per spike, wheat kernel) were determined. Results showed that planting methods did not affect wheat grain yield significantly. However, wheat grain yield was significantly higher for Kesht Gostar grain drill than the other two machines in two drier years. Mean wheat grain yield was 1224 kg ha–1. Mean wheat grain yield was the greatest (1275 kg ha-1) for Kesht Gostar and the least (1174 Kg ha-1) for Hamedani Barzegar grain drill. Mean straw yield was not affected by planting methods. Mean wheat straw yield was the greatest (2349 kg ha-1) for Hamedani Barzegar grain drill, and the least (2009 Kg ha-1) for the combination of seed broadcasting and disking. The amounts of rainfall during growing season strongly influenced wheat grain and straw yields. Mean wheat grain yield was 1572 Kg ha-1 and 1026 Kg ha-1 in wet year and dry years, respectively. This study showed that a wide range of grain drills is adaptable for dryland wheat cropping system for the semiarid Hamedan areas.

In the present research, susceptibility of two strawberry cultivars (Selva and Gavita) to bruising was studied. Individual fruits were subjected to impact and compressive forces. Impact forces were applied through dropping the fruits from predetermined heights as well as pendulum. Bruising volume was considered as damage index. In both methods bruising severity was increased as a function of impact energy. Dropped fruits were showed higher bruising volume than those of fruits impacted by pendulum for similar energy levels. Increasing energy level by a factor of four (from 0.022 to 0.082 J) caused the bruise volume to increase by a factor of three (from 46 to 134.5 mm3). Increasing drop height from 18 cm (0.026 J) to 54 cm (0.079 J) caused the bruise volume to increase up to 35%. Bruise severity due to compression force was higher than those of obtained from other tests. Doubling the loading time from 2 to 4 seconds showed no significant difference in bruise volume. Although Gavita variety had greater sensitivity to bruising than Selva variety, the effect of variety was significant only in impact test with pendulum tester.

The most important quality indicator of fruits is the flesh firmness which is well correlated to their young’s modulus. In this research variation of vibration characteristics (shape modes, natural frequency) of apple due to change of material characteristics (density, young's models, Poisson ratio) and apple volume was investigated using Finite Element simulation. An image processing technique was used to obtain an unsymmetrical and non-spherical geometric model of apple. The exact three-dimensional shape of the fruit was created by determining the coordinates of apple surface and forming uneven rotational curvatures. Modal analysis with no boundary constraints has been applied. The first 20 Eigen frequencies and the corresponding mode shape were determined. Six rigid body modes possess zero resonant frequency which is related to the degree of freedom of a rigid body in space indicated the validity of finite element model. The modal analysis results showed that resonant frequency increased by increasing young's modulus of the fruit, while it decreased by increasing apple density. First mode torsion has a mean resonant frequency of 584 Hz. Variations of natural frequency due to change in young's modulus, density, and Poisson ratio were 80%, 11% and 4%, respectively. Coefficient of variation of resonant frequency in response to changing young's modulus was 2-3 times of that of density which shows the greatest effect of young modulus changes on natural frequency of fruits. Consequently with determination of fruit's natural frequency, their young modulus and firmness can be estimated.

Safflower is a strategic plant regarding to its valuable nutrition value (45% extractable oil) and industrial uses. Due to massive import of edible oil to the country as well as high potential for safflower cultivation, the research on production of safflower for oil extrusion purpose is of remarkable importance. The design of various processing and oil extraction units and also their optimization which are in relation to seed attributes is essential. In this paper the effects of different irrigation and nutrient treatments on some important physical and mechanical properties of IL111 varieties of safflower seed were investigated. The measured properties included size, mass, volume, surface area, arithmetic and geometric mean diameter, sphericity, bulk and true densities, porosity, static and dynamic coefficient of friction, rupture force, deformation at rupture point, rupture energy, modulus of elasticity and seed hardness. The results indicated a significant effect of treatments on the biophysical and biomechanical properties at p ≤ 0.01. The maximum seed mass, geometric mean diameter and rupture energy were obtained when the (cg) treatment applied i.e. “Cut-off irrigation at the growth stage and bio sulfur nutrition”. Seed mass was found to be 0.040 gr to 0.055 gr. Results also showed a significant effect of geometric mean diameter on mass and rupture energy and also mass on seed hardness. Direct correlations observed between seed mass and rupture energy, which indicates that for larger and heavier seeds, much more energy required for oil extraction. The maximum rupture energy was measured as 0.033 J.