فصلنامه علوم زراعی ایران
سال هشتم شماره 2 (پیاپی 30، تابستان 1385)

Field experiments were conducted in 2002-2003 and 2003-2004 cropping season to determine the effects of crop rotation and N fertilizer on yield and yield components of two wheat (Triticum aestivum L.) varieties under Bajgah (near shiraz) dryland condition. Treatments included two rotations (wheat-lentil and wheat-fallow), three N fertilizer rates (0, 30, and 60 kg N ha–1), and two wheat varieties (Niknejad and Zagros). A split Factorial design with three replications was used. Interaction of nitrogen and variety on grain yield and yield components were significant, the highest grain yield obtained from 60 kg N ha–1 and Niknejad in two years (101.5 g/m2 at the first year and 125.7 g/m2 at the second year) and the lowest grain yield was obtained from 0 kg N ha–1 and Zagros in two years (71.3 g/m2 at the first year and 73.4 g/m2 at the second year). Maximum number of spike per m2 in the first year was obtained from 30 kg N ha–1 and Niknejad (271) and in the second year from 60 kg N ha–1 and Niknejad (282.9). Minimum number of spike per m2 was obtained from 0 kg N ha–1 and Zagros in two years (202 in the first year and 213.4 in the second year). Maximum number of grain per spike was obtained from 60 kg N ha–1 and Niknejad in two years (11 in the first year and 11.5 in the second year) and minimum number of grain per spike was obtained from 0 kg N ha–1 and Niknejad in the first year (8.2) and from 0 kg N ha–1 and Zagros in the second year (8.7). Interaction of nitrogen and crop rotation on grain yield and yield components was significant, the highest grain yield obtained from 60 kg N ha–1 and wheat-lentil rotation in two years (100 g/m2 at the first year and 120.4 g/m2 at the second year) and the lowest grain yield was obtained from 0 kg N ha–1 and wheat-lentil rotation in the first year and from 0 kg N ha–1 and wheat-fallow rotation in the second year (74 g/m2 at the first year and 76.8 g/m2 at the second year). Maximum number of spike per m2 in the first year was obtained from 60 kg N ha–1 and wheat-fallow rotation (266.7) and in the second year from 60 kg N ha–1 and wheat-lentil rotation (281.3). Minimum number of spike per m2 was obtained from 0 kg N ha–1 and wheat-fallow rotation in two years (207.2 in the first year and 218.7 in the second year). Maximum number of grain per spike was obtained from 60 kg N ha–1 and wheat-lentil rotation in two years (10.7 in the first year and 11.7 in the second year) and minimum number of grain per spike was obtained from 0 kg N ha–1 and wheat-lentil rotation in two years (8 in the first year and 8.7 in the second year). Increasing nitrogen level had no significant effect on soil organic carbon in the first year but, in the second year, maximum rate of soil organic carbon was obtained from 30 kg N ha–1 (0.99%), although 30 and 60 kg N ha–1 (0.95%) had no significant difference. In the first year, rotations had no significant effect on soil organic carbon, but in the second year, soil organic carbon was higher in wheat-lentil (0.96%) than wheat-fallow (0.90%).

In order to study the role of some metabolites as proline, soluble sugar, soluble proteins and inorganic solutes on osmotic adjustment mechanism and variation of water relationship in cutleaf medic [Medicago laciniata (L.) Mill] under drought stress, a greenhouse experiment was conducted in 2004, at the Agricultural Biotechnology Research Institute, Karaj, Iran- using a factorial arrangement in RCBD with three replications. Two genotypes of cutleaf medic, sensitive and tolerant to drought stress was treated in four levels of water stress including: -0.1, -0.2, and -1 MPa as low, medium and high stress levels, respectively and normal condition (FC = -0.03 MPa). Results indicated that high stress decreased RWC of sensitive genotype. Increases in organic metabolites accumulation as Proline, soluble sugar and inorganic solutes as potassium were associated with a decrease in osmotic potential in tolerant genotype as compared to sensitive genotypes. This study revealed that osmotic adjustment, through increasing slouble sugar and potassium ion was considered as an important mechanism for drought tolerance in annual cutleaf medic, as in tolerant genotype, it was almost twice in comparison with sensitive genotype.

Genetic diversity of 21 alfalfa (Medicago sativa) ecotypes collected from cold regions were investigated during1998-2001 at Neyshabour Agricultural and Natural Resources Research Station. The multivariate techniques were used for study the genetic variation among morphological traits. Factor analysis with Varimax rotation was performed on 23 variables and reduced them down to six common factors with 80.45% variance which were: vegetative factor (20.13%), forage yield components(16.64%), grain yield and it’s components (14.26%), forage quality(13%), reproductive length (9.24%), and reproductive factor (7.18%). Cluster analysis using WARD method classified the 21 ecotypes into four cluster. Ecotypes of second cluster for having high plant height, stem dry weight, re-growth rate, fresh and dry matter yield, were highly valuable for transferring their traits through hybridization programs. Also in cluster three, ecotypes No.9 is suitable for improving forage quality(Leaf/Stem ratio) and in cluster four (ecotypes from Chaharmahal-and- Bakhteyari), for improving inflorescent length and grain yield.s

To analyze the morphological changes affected by endophytes on induction of cold tolerance in two species of festuca, an experiment was done at Isfahan University of Technology in 2002.Endophyte-infected and non-infected clones from two genotypes of tall fescue and one meadow fescue were prepared and numbered 75,83 and 60 respectively. The clone were exposed to cold treatment at 20 C. After three weeks of cold treatments, shoot, root and crown dry weight, number of tillers, cuticle thickness and finally amount of regrowth were measured. The presence of endophytes had significant effect on increasing the dry weight of shoot, root, crown and number of tillers. Endophytic fungi had not significant effect in cuticle thickness. Evaluation of regrowth after termination of stress condition showed that endophytes increase the plant ability to survive and recover from exposure to cold stress environment. Among plant genotypes, 83 was better for most characteristics, specially in the presence of endophyte and showed higher cold tolerance

In order to study the effect of different levels of nitrogen and plant density under different moisture conditions on grain yield and yield components, biological yield and economic and biological water use efficiency of a maize hybrid (Zea mays L.) cv. SC. 704 a research was conducted in 2004 and 2006 cropping seasons, in experimental field in Agriculture and Natural Resources Sciences University of Khuzestan, Ahvaz, Iran. Irrigation treatments were implemented separately in three experiment in cluding. Optimum irrigation (I1), Moderate stress (I2) and Severe stress (I3) (irrigation treatments were applied based on depletion of 30%, 40% and 50% of field capacity, respectively). Until 4 to 5 leaf stage (seedling establishment stage) irrigations carried out after depletion of 30% field capacity in all treatments and after this stage irrigation treatments were applied. A split plot arrangement in Randomized Complete Block Design with three replication was used for each experiment. In each experiment three nitrogen levels (N1=140, N2=180 and N3=220 Kg N ha-1) were applied in main plots and three plant densities (D1=6, D2=7.5 and D3=9 plants m-2) were assigned to sub-plots. Results of combined analysis of variance indicated that the effect of moisture stress, nitrogen and plant densities on grain and biological yield was significant. The maximum grain yield (1050.2 gm-2) was harvested from optimum irrigation (I1). Severe moisture stress decreased the grain yield by 35% in comparison with optimum irrigation. This reduction was mainly due to reduction of grain number per ear and 1000 kernel weight. Grain yield increased with increasing nitrogen application. The yield difference between nitrogen levels was mainly due to positive effect of nitrogen on grain number per ear. The response of grain yield to increase in plant densities was positive. All yield components except number of rows per ear were sensitive to plant densities. Harvest index decreased as severity of moisture stress and plant densities increased, but there was no significant difference between different levels of nitrogen. Decreasing irrigation intervals increased economic and biological water use efficiency. The highest means of economic (1.71 kgm-3) and biological (3.28 kgm-3) water use efficiency, belonged to optimum irrigation. Increasing nitrogen application increased economic and biological water use efficiency. The response of these efficiencies to plant densities was also positive. Results of this study, suggest that; in order to increase input use efficiency and decrease the costs, nitrogen consumption rate, plant densities and available water in soil should be proportionated. Under moisture stress conditions, reduction in input levels, not only decreases the costs, but also increases the efficiency of resources used.

In order to study the effect of sowing date and plant density on quantity and quality of sweet corn SC.403, field experiments were conducted in Gorgan Reaserch Station during 2001-2003 growing seasons. In these experiments four sowing dates (April 9, April 29, May 19 and June 8) and four plant densities (45000, 55000, 65000 and 75000 plants per hectar) were evaluated in a factorial experiment (4 ×4) Using Randomized Compelet Block Design with four replications. Results showed that ear yield, ear lenght, can seed percent and ear harvest index was influenced by planting date. Maximum ear weight achieved in April 29 (20250 kg/ha). The ear yield was identical in this planting date with April 9, With dealy in planting dek anthesis period decreased and therefore ear yield reduced due to the reduction of growth period and high air temperature. Plant density effected the ear yield, ear length and harvest index. Although maximum ear yield was 18170 kg/ha in 75000 plants per hectar, but it decreased, with increase in plant density, Ear marketing, obviously decreased, not only for fresh consumption bat also for industry. Despite of significant increase in ear weight in 75000 plant per hectar it is recommended that for better marketing of sweet corn it should be planted with 55000-65000 plant per hectar in spring.

In order to study the effect of supplemental irrigation on yield and yield components of tobacco, an experiment was conducted at Guilan Tobacco Research Station in 2004 and 2005 croping seasons. A randomized complete block design with four treatments and three replications was conducted. Treatments were: no supplemented irrigation (SI0), supplemental irrigation till the end of flower bud forming stage (SI1), supplemental irrigation till the end of flowering stage (SI2) and supplemental irrigation till the end of growth stage or full irrigation (SI3) as control in each cropping season. The required water for each treatment was determined based on water holding capacity and maximum allowable deficiency (MAD). The soil water holding capacity was measured by using Pressure Plate. The time of irrigation was determined by using Tensiometer and soil was irrigated to the field capacity level. Leaves were harvested at six times. At flowering stage; leaf length, leaf width, plant height, number of leaf and leaf area index were recorded and after harvesting of leaves; fresh leaf yield, dried leaf yield, unit price, gross income per unit area, quality traits such as sugar and nicotine percentage were also measured. The combined analysis of variance showed that all of the traits except number of leaves per plant were affected by irrigation and a positive correlation was observed between increasing amount of water and the traits. The effect of year was not significant on the traits except for dried leaf yield as the mean of dried leaf yield decreased in the first year of study, due to the non optimum distribution of precipitation immediately after transplantation. The dried leaf yield increased in the second year of experimental. The mean dried leaf yield of (SI0), (SI1), (SI2) and (SI3) treatments were 2096.80, 2170.00, 1974.00 and 1302.00 kg/ha, respectively. Irrigation until flower bud forming stage had the highest water productivity index based on dried leaf yield and gross income in comparison to other irrigation treatments in this study. Therefore, application of supplemental irrigation and optimum usage of available water resources are essential in tobacco production.