Journal of Plant Ecophysiology
Volume:3 Issue: 2, 2011

In order to study the effect of different N fertilization levels and to determine the optimum N level and plant population of onion in autumn cultivation, a split-plot experiment on the basis of a Randomized Complete Block Design with three replications was conducted in Shahdad Region of Kerman, Iran in 2009-2010. Nitrogen fertilization was carried out at four levels of 0, 90, 180 and 270 kg ha-1 and the population was at four levels of 450 000, 550 000, 650 000 and 750 000 plants ha-1. The planting was in the form of transplanting and the studied cultivar of onion was Primavera. It was found that N level significantly affected yield, bolting percent, ring diameter, plant height and corm weight at 1% probability level and population impacted yield, bolting percent, ring diameter and corm weight at 1% level and plant height at 5% level. In addition, the interaction between these two factors was significant for corm weight at 1% level and for ring diameter at 5% level, but it was not significant for the other studied traits. It could be concluded that the application of 180 kg N ha-1 and the population of 550 000-650 000 plants ha-1 in autumn planting of onion in Shahdad Region would result in the best yield with lower bolting percent.

The study was carried out in Agriculture Research Station of Ardabil Branch, Islamic Azad University, Ardabil, Iran in 2009 as a factorial experiment based on a Randomized Complete Block Design with three replications. The first factor was planting date from May 20 until June 29 with 20-day intervals. The second factor was plant density at three levels of 20, 30 and 40 plants m-2 and the third factor was cultivar including Williams and LW17. It was found that planting date significantly influenced days to 50% emergence, 50% flowering and 50% pod formation at 1% probability level. The effect of planting date was significant on grain yield per plant and per unit area, pod number per plant and single-grain weight at 1% and on grain number per pod at 5% probability level. Plant density significantly impacted days to 50% flowering and 50% pod formation at 1% probability level. The changes in plant density (between 20 and 40 plants m-2) did not significantly influence grain yield per unit area, pod number per plant and single-grain weight, while grain yield per plant and pod number per plant were significantly affected by plant density. Grain yield and yield components did not have significant differences for the studied traits. Cv. LW17 was less sensitive to the changes in plant density than cv. Williams, so that the highest and lowest grain yield per plant of cv. Williams was obtained at plant densities of 20 and 30 plants m-2, respectively.

Eight advanced wheat genotypes with winter and intermediate growth types as well as cv. Shahriar and line C-80-4 were evaluated under normal irrigation and terminal drought stress conditions in terms of yield and the contribution of dry matter remobilization (DMR) from shoots in two separate experiments based on a Randomized Complete Block Design with three replications in Agriculture and Natural Resources Research Station of Ardabil, Iran in 2008-2009. Under both normal and post-anthesis drought stress conditions, there were statistically significant differences among the studied genotypes in terms of various parameters of DMR like its amount, efficiency and contribution to grain yield. In total, the amount, efficiency and contribution of DMR from shoots was higher under stress than under normal conditions which can be related to the loss of photosynthesis induced by stomatal closure and the lack of gas exchange. The highest percentage of increase in the amount, efficiency and contribution of DMR was observed in three sister lines of Yan 7578.128//Chil/1*Star, Yan 7578.128//Chil/2*Star and Yan 7578.128//Chil/3*Star and genotype LC 909 Mima and its seems that these promising lines can have a satisfactory yield under terminal stress conditions in cold climates of Iran.

The current study was carried out to study the traits affecting grain weight and the effects of some physiological parameters on grain yield of autumn wheat genotypes under optimum and drought stress conditions. So, 16 bread wheat genotypes were evaluated under optimum moisture conditions during growth season and under post-anthesis drought stress until physiological maturity based on a randomized complete block design with two replications. The measured traits included grain yield, grain weight, retranslocation of reserves from stem to grain, the efficiency of stem in translocating its reserves, the partial share of stem reserves in yield, biological yield, harvest index and stress tolerance index (STI). The results showed that grain yield had a high, positive correlation with biological yield under both optimum and stress conditions. The highest correlation coefficients were observed between grain weight with biological yield, the number of grains per spike and harvest index. Under stress conditions, only harvest index and yield had significant correlations with stress tolerance index of genotypes. Stepwise regression analysis under optimum and stress conditions showed that biological yield and harvest index were the most important components which explained the variations of grain weight.

The effect of potassium sulfate on drought tolerance of wheat was studied in which the first factor was five wheat cultivars (Kavir, Sistan, Roshan, Bam and Boulani) and the second factor was two K levels (0 and 100 kg.ha-1 potassium sulfate). Two separate experiments were carried out in drought stress and normal conditions and the data were combined for statistical analysis. The drought stress was imposed on the basis of 110 mm evaporation from Class A evaporation pan and the normal conditions were provided on the basis of conventional crop water requirement in the region. Drought stress resulted in the loss of all traits, particularly grain yield by 39.37%. Among grain yield components, grain number per spike and 1000-grain weight were more sensitive to drought stress than fertile tiller number. The significant, positive correlation between grain yield and grain number per spike (r = 0.77) under drought stress implied its importance for grain yield under stress. Cultivars showed different responses to moisture status. Although drought stress resulted in the loss of grain yield, cv. Bam was more drought tolerant than the other cultivars and produced fairly high yield. The application of 100 kg.ha-1 potassium sulfate increased grain yield by 8% under normal conditions and by 10% under drought stress compared to non-fertilized (control) treatment. The effect of K on increasing peduncle length, grain number per spike, grain number per plant, biological yield and grain yield was more under stress than under normal conditions. Under stress conditions, K application can mitigate drought-caused losses by keeping photosynthesis activity and/or preventing the loss of photosynthesis and assimilation. So, it improves drought tolerance under stress conditions.

Rice has the second highest worldwide cultivation area after wheat. Rice stem borer (Chilo suppressalis Walker) is a dangerous pest being able to destroy more than 50% of rice under favorable conditions. Given the abundance of silica in nature and its importance at various growth stages and in making the plants resistant to pests, the current study was carried out in the greenhouse of Agricultural Sciences and Natural Resources University of Sari, Iran in 2008 in order to investigate the effect of silica on morphological traits of rice and the feeding of striped rice stem borer. The study was conducted as a factorial experiment on the basis of a Randomized Complete Block Design with three replications. Silica was applied at four levels of 0, 5, 10 and 20 g. Also, three cultivars were studied including Partow, line 34 and Neda. The pots were enclosed with chiffon. The morphological traits were studied after sowing and cultivation operations. Also, the plants were infested by age-1 larvae of striped stem borer at vegetative stage and their resistance was examined. It was found that different levels of silica fertilization significantly influenced such traits as white head percentage, stem silica, leaf chlorophyll content, fertile tiller, and stem height. The highest effect on reducing the damages of striped stem borer was observed in the treatment of 20 g silica fertilization which increased stem silica content. Cv. Partow treated with 20 g silica showed 0.11% white head while it showed 18.10% white head when it was not treated with silica fertilizer. Furthermore, the highest leaf chlorophyll content and fertile tiller number of all the studied cultivars were obtained by the application of 20 g silica. It should, also, be mentioned that the highest stem height was obtained by the application of 10 g silica. Therefore, it is recommended to use cv. Partow and to fertilize it with 20 g silica.

The effect of micronutrients fertilization on yield, yield components and some quantitative traits of wheat was studied in Ardabil, Iran in 2009 growing season. The study was carried out as a Randomized Complete Block Design with three replications. The treatments included control and the combination of different concentrations of Fe and Zn fertilizers (2, 4, and 8:1000). Spike length and plant height were affected by fertilization treatments, so that the highest spike length was obtained from Fe3Zn1 treatment and the highest plant height from Fe2Zn3 and Fe3Zn1 treatments. The impact of fertilizers was significant on yield and yield components, too. The highest number of grains per spike was observed in Fe1Zn2 fertilizer combination which was 22.7% higher than that of control. The highest 1000-grain weight (57.6 g) was obtained from Fe3Zn1 treatment. However, there was no significant difference between Fe1Zn3, Fe2Zn1, Fe2Zn2 and Fe3Zn2 treatments, which were ranked after Fe3Zn1 treatment. The application of Zn and Fe micronutrients brought about significant differences in grain yield and the highest grain yield (9732.2 kg ha-1) was obtained from Fe1Zn2 treatment although showing no significant differences with that of Fe1Zn1, Fe2Zn1 and Fe3Zn2 treatments. The highest harvest index was observed under Fe1Zn2 treatment.

Soil organic carbon (SOC) has an important influence on soil properties, soil fertility, land degradation, food security, and global warming. One of the important issues in agriculture is the empirical relationship between some soil properties and SOC, which is expressed as pedotransfer function (PTF). The objectives of this research were to (i) investigate the possible factors influencing SOC such as topography aspect, elevation and slope, and (ii) develop pedotransfer functions for estimation of organic carbon in some land types of Damavand region in Northeast of Tehran, Iran. Lower SOC~4.9 g kg-1 concentration was associated with higher elevation and north-face slopes in plateau physiography due to lower temperature and plant biomass. In the lower elevation, especially in valley physiography, there was the highest SOC content (22.04 g kg-1). This land type was used as the garden utilization type. The data analysis showed that SOC was significantly correlated with total area elevation (r = −0.521**, P < 0.01). It was also found that the elevation affected SOC status significantly in all land types. Pedotransfer functions and simple linear regression (r = 0.521**, P < 0.01), multiple linear regression (r = 0.544**, P < 0.01) and nonlinear regression (r = 0.588**, P < 0.01) models were also developed for predicting SOC. Correlation coefficients of three regression methods in each land type were compared using homogeneity of correlation coefficient test. There were significant differences (R2 = 0.99**, P < 0.01) among all land types. These patterns were closely related to the topography and land use type.