Iran Agricultural Research
Year:2006 | Volume:24-25 | Issue:1-2|Papers Count:9

Soil water content is one of the most important parameters for estimating irrigation frequency and providing the plant’s water requirement. Since measurement of soil water content is both expensive and time consuming, water movement models are used to estimate these values. In this study, LEACHW model was used to estimate soil water content for two “dry” (20-29 Aug) and “wet” (1-6 Jul) periods during the 1995 growing season. Different values of hydraulic parameters were applied to investigate the sensitivity analysis of these parameters in the estimation of soil water content. Thus the values of b (pore distribution coefficient in Campbell’s equation (2) were selected from 2 to 24, and k(q)/ks ratios of 0.1, 1, 10 and 100 were used. Finally 32 treatments were investigated for each period. Results showed that despite large variation for the hydraulic parameters, similar trends of results were obtained for all soil water content estimations. Statistical analysis comparing the estimated and measured results showed a systematic difference which can be adjusted using a few measured values of soil moistures. As an example, simulated results using b=24 and k(q)/ks=0.1 were calibrated to adjust the simulated results. The results of this study showed that a simple calibration method can be used for the estimation of soil moisture content without using extensive data required to represent hydraulic characteristics of soils.

Although inter-variety variability for salt tolerance has been reported in bread wheat plants, little information is available on the genetic control of ion contents and biomass yield under saline conditions. A diallel cross, including reciprocals of two salt tolerant, two moderately tolerant and two sensitive Iranian and exotic bread wheat varieties, was analyzed to investigate the inheritance of ion contents in young leaves at the seedling stage, and biomass yield (BY) and stress tolerance index (STI) at maturity. Specific reciprocal effects were also studied in F2 populations derived from some F1 reciprocal crosses. The materials were evaluated in a gravel culture under high salinity (EC=22.5 dSm-1) and non-stress (control) conditions. Dominance gene effects were more important for Na+, K+ concentrations, K+/Na+ ratio and BY in control, but  both additive and non-additive effects were observed for BY, K+ concentration and STI in salt stress condition. Significant general and specific maternal effects were observed in F1 generations for all traits, except for BY in the saline condition. Significant general and specific reciprocal effects indicated cytoplasmic and cytoplasmic × nuclear genes interaction in the response to salt tolerance, respectively. The most tolerant parent, ‘Roshan’ was the best combiner parent for related salt tolerant traits followed by ‘Kharchia’. The results obtained from maternal effects in F1 and F2 generations indicated that ‘Roshan’ was more salt tolerant when used as a female parent. Some crosses in the tolerance×sensitive, tolerance×tolerance and moderately tolerant×sensitive groups proved to be the best combinations for obtaining desirable segregants for salt tolerance based on their per se performances, specific combining ability and heterotic effects.

The aim of this study was to determine the most suitable shaking frequency and amplitude for shake harvesting lime fruit (C. aurantifolia). A tractor mounted limb shaker with adjustable shaking frequency and amplitude, powered by the tractor power-take-off shaft was designed and developed for this study. The rotating input power was transmitted to the shaker flywheel through a multiple sheave v-belt drive system where it was converted to reciprocating motion by a slider crank mechanism. The resulting vibrating motion could be transmitted to the tree limb through a telescoping boom and a special clamping device. A 3×3 factorial experiment arranged in a completely randomized design with three replications was conducted to investigate the effects of shaking frequency and amplitude on fruit detachment. Three levels of oscillating frequency (5, 7.5 and 10 Hz) and three levels of shaking amplitude (40, 80 and 120 mm) were investigated. Analysis of variance and mean comparison showed that the effect of shaking frequency on fruit detachment was significant. However, those of shaking amplitude and its interactions with frequency were not significant. The percentage of detached fruits significantly increased by increasing the shaking frequency, but the shaking frequency or amplitude had no significant effect on fruit damage. Complete fruit detachment (100%), was obtained by applying shaking amplitude of 120 mm at a frequency of 10 Hz, but considerable leaf removal at this combination of shaking frequency and amplitude was a limiting factor. Therefore, shaking the limbs at 80 mm amplitude and 10 Hz frequency with about 98.5% fruit detachment and negligible leaf shattering was found to be the most suitable combination. In order to determine the bonding strength of lime fruits, a series of tests were conducted in which, the average pulling force required for detaching ripe and unripe fruits as well as fruit mass and geometric mean diameter were measured. The average static force required for removing ripe fruits was found to be about 14.2% of that required for removing unripe fruits. The average ratio of tensile force required for removing a fruit to its weight (Fs/W) was measured as 6.9 and 61.8 for ripe and unripe fruits, respectively. The two indices suggest utilizing a limb shaker as a valuable approach for selective harvesting of ripe fruits. This is especially true for fruit varieties with non-uniform ripening characteristics.

The aim of the present investigation was to study the growth, yield and yield components of maize (Zea mays L.) single cross 704 under different levels of irrigation, plant density, and ethephon in southern Iran where this particular crop has not yet been studied in detail. A field experiment was performed in the 2004 5 growing season at the experimental farm of the College of Agriculture, Shiraz University, Shiraz, Iran, located at Badjgah. The experimental design was a randomized complete block with four replicates where the treatments had a split split plot arrangement. Irrigation level (low and high) was the main plot, plant density (53,333 and 80,000 plants/ha) the subplot, and ethephon level (0, 0.56, 0.84 kg/ha a.i., applied at the 6 leaf stage) the sub subplot. The results showed that the rates of foliar application of ethephon could play an important role in maize growth indices, and attribute to grain yield components. Application of ethephon was associated with a decrease in Leaf Area Index (LAI), Leaf Area Index Duration (LAID) and Crop Growth Rate (CGR). Furthermore, ethephon reduced plant and ear height. Increasing the application rates of ethephon showed a significant reduction in early season plant height and LAI, LAID. The control plants had lower grain yield than those treated with different rates of ethephon. Indeed, this research showed that under conditions of water stress, the maize plant is able to make better use of available water if vegetative growth is partially restricted early in the season. The results also indicated that the yield response of maize to ethephon application would vary with plant density and available water conditions. Ethephon treatment was found to be more beneficial for grain yield with higher plant densities and under water stress conditions. 

A study was conducted to compare the performance of four types of planter furrow opener and row cleaner arrangements at two crop residue levels on the amount of surface residues after planting, seeding depth, emergence rate index and seed spacing indices of corn in a soil covered with previous wheat residue. Residue levels were baled out and non-baled (untouched). Corn was planted with a planter equipped with the following furrow openers and attachment arrangements: double disc furrow opener preceded by a row cleaner (DR), chisel furrow opener preceded by a row cleaner (CR), winged chisel furrow opener preceded by a row cleaner (WCR) and winged chisel furrow opener without row cleaner (WC). Results showed that WCR treatment at baled out residue level retained the least amount of residue on the seed row after planting. Measurements showed that residue level for all treatments were higher than the residue level required for establishing conservation tillage practices.  An increase of ERI up to 15% was obtained for this treatment as compared to CR and WC treatments. Double disc furrow opener preceded by row cleaner treatment resulted in higher percentage of ERI as compared to CR and WC, possibly due to less planting depth. The study showed increasing depth is more influenced by furrow opener shape than the amount of bed residue. The lowest miss index was obtained for WCR treatment at baled out residue level which is desirable. Improvement in quality of feed index was found to be 36% for WCR treatment when compared to planting with DR and WC treatments. Furthermore, this treatment decreased the value of precision index up to 45% as compared to DR and WC treatments.

The present study is based on the investigation of a soil hyphomyces, Paecilomyces lilacinus, an opportunistic bio-control agent, in controlling root-knot nematode Meloidogyne javanica on tomato in greenhouse conditions. P. lilacinus, effectively promoted the growth of plants inoculated with M. javanica by suppressing its pathogenesis as root galling by the nematode and egg mass production was greatly reduced. The fungus was most effective when the fungus and the nematode were inoculated simultaneously or the fungus preceded the nematode in sequential inoculation. Conversely, when the nematode preceded the fungus, the improvement in plant growth and reduction in root galling and egg mass production were not substantial. A great number of nematode eggs were infected by P. lilacinus, inhibiting juvenile development. The interior of eggs, were devoid of juveniles and filled by the fungus mycelium. Developed juveniles were found attacked and/or killed and showed mycelial growth over their bodies. Simultaneous inoculation or sequential inoculation in which the fungus was added prior to the nematode was more effective in controlling the nematode than when nematodes preceded the fungus. P. lilacinus was, therefore, effective in controlling the root knot nematode on tomato and suppressing its population growth.

Wheel numeric and different versions of mobility numbers are important models for predicting the rolling resistance. In this study, data related to the rolling resistance of cross ply and radial ply tires were compared with the resultant values from several models. Also, the preciseness of models in rolling resistance prediction was evaluated. For this purpose F test and 1-1 line method (p³0.05) were used. According to the results of the evaluation, Cn and Bn models overestimated the rolling resistance for both cross ply and radial ply tires, but the slope of these models did not show any significant difference compared to 1-1 lines. Results indicated that these models had better prediction if an adjusting coefficient could be applied. The EMOB model showed better results compared to Cn and Bn models for cross ply tires, whereas it did not have acceptable predictions for radial tires. The N.I.A.E., FMOB and Dwyer models did not act well for any tire type, even though the best fit line of the Dwyer model did not show any significant difference with the 1-1 line for cross ply tires.