JWSS - Journal of Water and Soil Science

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To increase mechanized cotton planting in areas with saline irrigation water and crust forming soil in Isfahan Province, assessment of seeders in flatland planting method with or without crust breaking is essential. An experiment was conducted at the Kabootarabad Research Station of Isfahan Research Center to compare the performance parameters of planting equipment in a clay loam soil. Four planting equipment treatments using Bazrsazan and John Deere planters and Nordsten drill along with three crust breaking methods, including rolling cultivator, rolling-type crust breaker and no crust breaking, were laid out in a factorial experiment within a randomized complete block design with three replications. Planters’ performance was evaluated by measuring the number of plants and plant spacings in each treatment, and estimation of the mean and standard deviation, multiples index, miss index, quality of feed index, precision, and hill-dropping index. Although the plant spacings, and not the seed spacings, were measured in this experiment, the indices used in this research showed the planters’ performance to be very satisfactory. The suggested hill-dropping index showed the multiple seeds dropping characteristics of the seeders to be better than those of the multiples index regardless of the crust breaking methods. In the non-crust breaking method, the multiple seeds dropping tendency of Bazrsazan planter brought about a reduction in the mean and standard deviation of plant spacings. Crost breaking caused a reduction in plant spacings for all seeders, especially for the drill whose multiple seeds dropping tendency was negligible. The results indicated that the seed metering systems in Bazrsazan and John Deere planters were volumetric rather than single seed metering devices.

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Soil tilth is crucial to seedling emergence, plant growth, and crop yield. Soil tilth of unstable soil is very susceptible to change. Internal forces originating from matric suction can change soil physical properties. A laboratory study was conducted on pots of a surface silty clay loam soil of Khomeinishahr series (fine-loamy, mixed, thermic Typic Haplargids, USDA), located in Research Farm of Isfahan University of Technology. Soil surface subsidence, bulk density, cone index, and tensile strength were measured after first flood irrigation. Results showed that the seedbed (0-20 cm) with a bulk density of 1.2 Mg.m^-3 will be changed to a massive soil with high values of bulk density, cone index, and tensile strength after soil wetting. Slaking, slumping and coalescence of the soil caused soil surface to subside about 1.5 cm in 20 cm soil layer. After irrigation, cone index and tensile strength increased abruptly with decreasing of moisture content. It is shown that the dominant source of strength (cone index and tensile strength) gain during drying is the effective stress due to matric suction. In the absence of external loads, physical state (tilth) of the soil returned back to the original state. Therefore, soil slaking and slumping and rearrangement of particles along with the internal forces are the factors leading to soil hardness.

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Differential lock is a means of improving tractor performance. This system causes the revolution of the axles to become equal. It, improves traction, decreases abrasion of drive tires, improves fuel consumption, and increases tractor work rate. Despite advantages of the system, differential lock has not been optimized in Iran. Thus, a semi-automatic differential lock system for MF-285 tractor was designed and developed. First of all, the different parts of the system were designed, selected, assembled. Under critical conditions, the designed system should disengage the differential lock. Critical conditions for engaging this system are: using of independent brake pedals, high forward speed, and turning the steering wheel. For sensing and measuring the critical conditions, proper sensors were selected. Output signals of these sensors were sent to a micro controller to decide the continuous engaging or disengaging. Finally, a MF-285 tractor was equipped with the designed system. The tractor performance in primary tillage was evaluated using a mounted moldboard plow with a width of 110 cm and a working depth of 25 cm. These tests showed that unbalanced weight distribution on wheels and unequal traction capacity under drive wheels cause the slip of one wheel to be 6 percent higher thananother. This system improves the unequal slip problem and decreases fuel consumption by 0.5 L/ha.

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Studies show that excessive rotation of rice, when the grains revolve inside the milling chamber, increase the breakage. Ease of grain movement in the milling chamber could minimize this problem by utilizing screw conveyor at the first part of rotor. In this study the rotor of a conventional milling was equipped with a screw conveyor. The effects of two rotor types (modified and conventional rotors), three output rates (412, 654 and 915 kg/h) and three blade distances from the agitator (11, 12 and 13mm) were examined on indices of rice quality using a split-split plot design. In this experiment, the percentage of whole white rice and breakage, degree of milling and milling performance index were either measured or calculated. Results showed that only the effect of blade distance on percentage of breakage was significant whereas the effect of feed rate on all measured parameters was significant. In addition, the interaction effects of rotor type and blade distance, rotor type and feed rate on percentage of whole white rice and breakage were significant, respectively. The milling performance index showed that the best conditions for both rotors can be obtained at output rate of 412kg/hr and 11or 12mm blade distance from the agitator. For this adjustment, the average of percentage of breakage in the modified and conventional rotors were 20.5 and 23, respectively.

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For measuring draft force and drawbar power requirements for mounted implements, precise instruments such as three-point hitch dynamometers and tractor speed measurement devices are needed. In this research, a frame-type three-point hitch dynamometer was built and evaluated. Forces applied to dynamometer are measured by three separate load cells located on a frame which can be attached to tractor’s three-point hitch. Each dynamometer’s load cell measures load using a strain gauge bridge circuit. Each load cell was calibrated by applying a known load and measuring bridge circuit’s output voltage. Dynamometer was calibrated by the application of known forces and measuring the output voltage of the strain gauge bridges. The calibration showed a high degree of linearity between the applied forces and the bridge outputs (R² = 0.996). The hysteresis effect between loading and unloading as well as the effect of the position of the applied forces from the longitudinal axis of the dynamometer was small. For measuring actual tractor speed, a fifth wheel equipped with an encoder shaft was designed and built. The calibration on tarmac and soil surfaces showed a highly linear relation between measured forward speed and output of encoder’s rotation (R² =0.994). The errors in speed measurements at low speed in field and at high speed (up to 12.5 km/h) on tarmac surface were approximately 3 and 8%, respectively. The data acquisition system, not only could display the instantaneous force and speed, it could also show force-time and force-distance curves on the system’s monitor.

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One important parameter in determining the allowable stress to prevent soil compaction is pre‌compaction stress (σpc). If the stress induced into the soil due to agricultural machinery traffic is lower than the σpc, the possibility of the irreversible (plastic) deformation is low. In this study, plate sinkage test (PST) and confined compression test (CCT) were used to determine the σpc of the disturbed soil samples obtained from the topsoil of a long-term organic amendment experiment. In the organic amendment experiment, organic manures (sewage sludgeو compost, farmyard manure) at three rates (25, 50 and 100 t ha-1) and one inorganic fertilizer combination (250 kg urea ha-1 and 250 kg ammonium phosphate ha-1) were added to a silty clay loam soil for seven years under wheat-corn rotation. The effect of organic and inorganic fertilizers and gravimetrical water contents (17.1 and 20.9% db) on the σpc values was determined using two statistical designs: 1) factorial design and 2) orthogonal contrasts in a completely randomized design with three replications. The σpc values were estimated by the following methods: 1) Casagrande, 2) maximum curvature and 3) intercept of virgin compression line (VCL) with the x-axis at zero strain. The results showed that in both tests, the σpc values for treatments amended with organic manures had over-estimations and the values of the over-estimation were increased as the manure application rate increased. The values of the over-estimations for CCT were higher than for PST. Therefore, it can be concluded that the results of the PST are more reliable. The σpc values estimated by any of the three procedures depend on the manure treatment as well as the initial water content of the soil. For determining the stress at the threshold of the compaction for the un-manure soils (control and inorganic fertilizer) or the treatments amended with low application rate (25 t ha-1) of the organic manures, the PST and the Casagrande procedure can be recommended. In contrast, for the soils amended with high application rates (50 and 100 t ha-1), the PST and the maximum curvature procedure can be used.

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Puddling is the most common method of land preparation for lowland rice cultivation. The purpose of this study was to assess the influence of various intensities of puddling on percolation rate, water retention by soil and the amount of water used for different puddling intensities in three dominant soil textures of paddy fields in Guilan province. Undisturbed soil samples were taken from 3 different soils including silty clay, clay loam and loam, with 3 replications. The soil samples were puddled by a laboratory apparatus with different intensities. The results showed that the low puddling intensity treatment caused a 29.3, 32.4 and 36% reduction of percolation rate in silty clay, silty loam and loam textures, respectively. Increasing puddling intensity from low to medium reduced percolation rate significantly, but high intensity was not effective. Soil moisture characteristic curves of all three soils showed that water retention was increased by puddling treatments. Water retention in silty clay was higher than the other two soils. The high intensity treatment needed more water than low intensity for puddling. Increasing puddling intensity from medium intensity to high intensity caused 15.4, 14.1 and 16.3% increase in the amount of water required for puddling in silty clay, silty loam and loam textures, respectively. Generally, in all the three studied soil textures, the amount of water used for high-intensity puddling was more than medium-intensity puddling, while it had no significant effect on water percolation rate and soil water retention.