JWSS - Journal of Water and Soil Science

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Planting density, through its impact on the level of available environmental factors may have significant impacts on grain yield in safflower (Carthamus tinctorius L.). In order to investigate the impacts of plant density on grain yield, yield components and growth characteristics of safflower, a randomized complete block design field experiment with four replicates was conducted in spring-summer, 2000, at Lavark Research Farm (Lat. 32⁰ 32^, N and Long. 51⁰ 23^, E), College of Agriculture, Isfahan University of Technology, Isfahan, Iran. Arak-2811 and Kouseh safflower genotypes were seeded at 16.6, 22.2, 33.3 and 50 plants/m². For establishing these plant densities, plants were seeded in 12, 9, 6 and 4 cm distances, respectively, on ten 8-m-long rows spaced 50 cm apart in each plot. Plant density had no impact on plant growth stages with the exception of button formation. Genotype had significant effects on days to seedling emergence, button formation, and 50% flowering. While both number of days and accumulated growing degree-days for all growth stages decreased with an increase in plant density, Arak-2811 was earlier than Kouseh for most growth stages. Number of branches and heads per plant, number of heads per branch, number of seeds per head and harvest index showed significant decreases with increasing plant density. The decrease in the mentioned grain yield attributes was mainly negated by greater number of plants per m², leading to no significant variation in grain yield between plant densities of the two genotypes. Arak-2811 produced a significantly greater number of heads per branch and 1000-grain weight however, these differences did not lead to any greater grain yield compared to Kousehdue, mainly due to the greater number of branches in the latter. Neither of the leaf area index, leaf area duration, and crop growth rate varied significantly with plant density and between two genotypes, suggesting no difference in dry matter production capabilities of the two genotypes under environmental conditions of the present study.

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The physiological characteristics of winter wheat(cv. Shiraz) were evaluated in a 2-yrs field study by using a spilit plot design with four replications, at the experimental farm of Shiraz University, College of Agriculture located at Badjgah. Main plots consisted of three sowing dates (November 6^th, December 6^th and January 5^th) and four planting densities (150, 250, 350 and 450 plants/m²) were assigned as sub plots. The results indicated that delay in sowing was associated with a significant reduction in the grain yield. So that the grain yield in sowing date of January 5^th was significantly less than it in sowing dates of November 6^th and December 6^th. Moreover with delay in sowing date the developmental rate of wheat was enhanced and plants reached maturity more rapidly. The trend of the leaf area index changes and the dry weight of the plants were under the effect of experimental treatments, leaf area index was found to be greater at the higher densities and early planting date. Number of stems per m² were decreased with delay in the sowing date, although at the higher densities, the number of stems per m² was greater, despite severe tiller death observed at these densities. The study of trend of dry weight changes during the season indicated that biomass was greater at higher densities and earlier sowings, which resulted in earlier ground cover and higher amount of radiation interception. In conclusion, the results of the present investigation revealed that to achieve a reasonable grain yield, the 6^th of December and 250 plants per m² were the best sowing date and planting density for wheat (cv. Shiraz) under similar agro climatic conditions with the present investigation.

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Drought is a major factor limiting growth and development of crops such as mung bean (Vigna radiate (L.) wilczek) in arid and semi-arid regions of the world. This study was conducted to investigate the effects of different timing and severity of drought stress on physiological traits of mung bean and its relation to grain yield. A field experiment was carried out during 2004 growing season at Experimental Farm of Agriculture College, University of Tehran, Karaj, Iran. The treatments were laid out in a Randomized Complete Block Design (RCBD) with three replications. Plants were exposed to moderate and severe water stresses at either vegetative (VS) or reproductive stages (RS). Physiological traits were measured at the end of vegetative and the middle of pod formation. Generally water stress reduced leaf net photosynthesis rate, stomatal conductance and leaf relative water content at different growth stages. The effects of RS treatments were more severe than that of VS one. Severe VS treatment increased photosynthetic water use efficiency, whereas RS treatments decreased it significantly. However, leaf area index and total dry matter were more responsive in VS compared to RS treatments. VS treatments did not affect harvest index, while RS treatments reduced it significantly. Drought stress also reduced grain yield by 9 and 49 % (relative to control plants) in severe VS and severe RS treatments, respectively. Therefore irrigation is critical during reproductive stage mainly because of the higher demand for photoassimilate. It is concluded that to maximize mung bean grain yield in arid and semi-arid areas, appropriate watering should be practiced across all phenological stages in general, and during reproductive stage in particular.

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Oil seed rape (Brasica napus) is an important crop, which is cultivated in Iran for oil production. As a management practice deficit irrigation strategy is applied to cope with water shortages, especially during drought periods. This research was conducted to study the effect of water stress on physiological parameter of oil seed rape in the experimental research field of Collage of Agriculture (of shiraz university) during 2004- 2005 and 2005- 2006. Licord cultivar of oil seed rape was planted and experimental design was random block with five treatments and four replications. Treatments were full irrigation in all growth stages, water stress in vegetative stage in early spring, water stress in flowering and podding stages, water stress in grain filling stage and dry land treatment with supplemental irrigation in time of planting. Water stress caused decrease in water potential of plant, an increase in canopy temperature, and decrease in plant height especially in dry land treatment. Leaf area index decreased as water stress increased. The decrease in leaf area index was more severe in vegetative stage water stress treatment. At the end of water stress period leaf area index increased again. Rate of decrease in leaf area index at the end of the growing season was higher in grain filling stage of water stress treatment.

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