مجله تولید گیاهان زراعی
سال چهارم شماره 4 (زمستان 1390)

One of the main problems in crop production in Iran is the difference between actual yield and attainable yield which is called yield gap. Thus, identifying yield constraints and yield gap are important. To do this, a study was conducted in 95 farms Gorgan of in five villages, during two years 2007 and 2008. In this study, all of the information about management operations, soil and crop characteristics were recorded and measured (including 200 variables). Then, relationships between variables and yield were considered (using stepwise regression). The results showed there is a 2348 kg/ha difference (gap) between actual yield (average farmer's yield) and attainable yield (maximum farmer's yield). It was identified that rate of potassium fertilizer before planting, rate of nitrogen fertilizer after planting, leaf area index at anthesis, leaf chlorophyll index at anthesis, total nitrogen uptake at maturity and the length of vegetative growth period were responsible in creation of yield gap with contribution of about 20, 18, 19, 10, 14 and 19%, respectively. Data investigations revealed that leaf area index at anthesis, leaf chlorophyll index at anthesis and total nitrogen uptake at maturity were controlled by nitrogen fertilizer management. Also, the length of vegetative growth period was controlled by planting date. Thus, it was then concluded that rate of applied potassium, nitrogen nutrition management and planting date are the most important responsible factors in creating yield gap with contribution of about 20, 61 and 19%, respectively. Optimizing of these factors could be increase wheat yield in Gorgan up to 2348 kg/ha.

In order to study the effect of irrigation cut on dry matter remobilization and some of agronomy traits on spring barley, a field experiment was conducted by using a split-plot based on randomized complete block design (RCBD), in three replications, at agricultural and natural resource research center of Ardebil, in 2009. Irrigation treatments included normal irrigation (as local routine in past years), no-irrigation and irrigation cut at stage an thesis substituted in main plots, and spring barley genotypes, EBYTW-11, EBYTW-2, EBYTW-3, and EBYTW-7 were placed in sub-plots. Results showed that amount, efficiency and contribution of dry matter remobilization from various organs of plant to grains were increased with irrigation cut, so that the contribution of dry matter remobilization at no irrigation treatment and irrigation cut in stage an thesis were estimated 67.8 and 38.0 percent, respectively, higher than that normal irrigation treatment. Means comparing of interaction effects showed that EBYTW-2 genotype had higher dry matter translocation (culm and various organs total) and contribution to grain yield. the highest dry matter efficiency of culm and leaf was belongs to EBYTW-3 genotype and the highest dry matter efficiency of peduncle was obtained from EBYTW-11 genotype in no irrigation and irrigation cut at an thesis stage treatments, respectively. The plant height, head and panicle length decreased at no irrigation rather than normal irrigation treatment (33.9, 24.5, and 11.9 percent, respectively). Results showed this reduction were 47.4 and 16.9 percent for grain yield, also 36.6 and 9.9 percent for biological yield at no irrigation treatment and irrigation cut at thesis stage in compared with normal irrigation treatment. The EBYTW-2 genotype in head length, 1000-grain weight, grain and biological yield had higher value than other genotypes.

In order to investigate the yield and yield components of four lentil genotypes (Local line, Local bulk, ILL-10314 and ILL-6037 genotypes) as affected by three urea nitrogen levels including 0, 45 and 90 kg ha-1, a factorial experiment based on randomized complete block design with three replications was carried out in agriculture and natural resources research center of Ardabil, during 2008. Based on the results, different nitrogen levels, except for grain yield, agronomical and recovery nitrogen use efficiency, did not affect the other studied traits. While the impact of genotypes was significant on all traits. Local line had the lowest number of full pods, number of grain per pod and grain per plant, showed the highest grain yield. The lowest grain yield was observed in the ILL-10314 genotype. Lower 100- grain weight in this genotype may be of the reasons for the low grain yield despite of the high number of grain per plant, grain per pod and the full number of pods per plant. The lowest number of the full pod per plant was observed in ILL-6037 genotype. This genotype having the highest 100-grain weight was placed in the same group with the local line and bulk, in terms of grain yield. The highest agronomical and recovery nitrogen use efficiency were achieved using the 45 kg ha-1 and Local bulk genotype.

In order to study effects of competitive weeds (Sinapis arvensis, Hordeum spp., Secale montanum and Agrostemma githago) on morphological traits, yield and harvest index of winter rapeseed (Brassica napus L.) cultivars a factorial experiment was conducted in Islamic Azad University of Tabriz, during 2007- 2008. Experimental factors were weeds controlling times included weeding in rosette (5-7 leaves stage), early stem elongation, early flowering and 50% flowering stages, full season competition and control; and Opera, SLM046 and Okapi cultivars. Results showed that number of branches per plant in control and full-season interference treatments were 4 and 2, respectively. Rapeseed biomass in whole season weed-infested plots reduced 40%, as compared with control. Weeds biomass in treatments those weeds were controlled at early stem elongation, early flowering and 50% flowering stages with 92, 86 and 87 g m-2 had non-significant difference. Weeds could increase biomass up to 410 g m-2 when grew with rapeseed along the season. Weeds controlling at rosette, early flowering and 50% flowering stages with 32%, 44% and 50% reduction value in seed yield, respectively, had significant difference with weed-free plots. When the weeds competition period extended a long time, allocation of biomass to seeds decreased. Seed oil percentage was not affected by cultivars and weeds competition periods. Reduction value in oil yield of rapeseed in different levels of weeds control were 32, 4, 45, 50 and 55%, respectively. Weeds controlling once in early stem elongation of all studied cultivars of rapeseed was recommended.

The aim of this research was to investigate the response of more and less competitive rice cultivars to different densities of barnyardgrass. A field experiment was conducted in 2010 in Tonekabon’s rice research station in Mazandaran province. The experiment layout was a factorial design with four randomized complete blocks. The experimental factors were six densities of barnyardgrass (0, 8, 16, 24, 32 and 40 plant per square meter) and two rice cultivars (Khazar and Line 843). Results showed that rice grain yield, fertile tiller number m-2 and grain number per panicle were decreased as barnyardgrass density increased from 0 to 40 plants m-2. However, the percentage reduction in grain yield, fertile tiller number and grain number per panicle increased more sharply in Khazar cultivar than in Line843 as barnyardgrass density increased from 0 to 40 plants m-2. On the other hand, biomass and seed production of barnyardgrass was increased more sharply in Khazar cultivar than in line 843 as barnyardgrass density increased from 8 to 40 plants m-2. In other words, line 843 compared to Khazar cultivar, could significantly reduce biomass and seed production of barnyardgrass under competitive conditions.

To evaluate the effect of different rates of nitrogen fertilizer on competitive ability of canola (Okapi cv.) in interference with wild mustard, a split-plot experiment based on a randomized complete block design with 3 replications was carried out at agricultural faculty of Bu-Ali Sina University, in 2008-2009. 4 levels of nitrogen fertilization (100, 150, 200 and 250 kg N ha-1) were assigned to mainplots and plant density of wild mustard at 5 levels (0, 4, 8, 16 and 32 plants m-2) to the sub-plots. The results showed that with increasing nitrogen application, were improved the canola vertical distribution of LAI and dry matter in pure condition and interference of wild mustard. Increasing wild mustard density led to decreased sum of canola and wild mustard yield in unit area. Nitrogen up to 150 kg ha-1, increased grain yield of wild mustard at all levels density. Increase up to 200 kgN ha-1, led to slight reduction of economic threshold of wild mustard on canola yield, but in 250 kg N ha-1, economic threshold value was less than a wild mustard plant in square meter. Overall the findings suggest that nitrogen application to 200 kgN ha-1 caused increases in competitive ability of canola against in wild mustard.

In order to investigation of planting pattern and plant density effects on vegetative and reproductive organs and yield of early maturing cotton cultivars, an experiment was carried out as split–split plot using randomized complete block design with 4 replications, in Karkandeh research station, during 2004-2205. Three row spaces (60, 70 and 80 cm) were consisted as main factors, plant space in the row of 10 and 20 cm as sub-factors and three early maturing cotton cultivars (Mutagenesis, B-557 and 43259) as sub-sub-factors. The results showed that with decreasing the row spaces from 80 to 60 cm, the average of the boll numbers per plant and single boll weight were decreased, but yield was increased from 2270 to 5656 kg ha-1 by increase in plant number in hectare. With decreasing plant distance from 20 to 10 cm, also, the plant height, monopodia length, sympodia length, sympodia number and boll number per plant were decreased. The best pattern for Mutagenesis cultivar was observed in planting pattern of 60×10 cm and density of 167000 plants per hectare. But the increasing of plant population had less effect on 43259 and B-557 cultivars.

In order to study the genetic diversity and the relationship between yield with some morpho-physiological traits, 81 wheat landraces including four check cultivars (Kavir, D.C. Shahi, Ws-82-9 and Roshan) were planted in alpha-lattice design in two replications under drought stress at the research field of Seed and Plant Improvement Institute (SPII), Karaj, during 2007-2008. Results showed that grain yield and its components, penultimate dry weight, harvest index, peduncle dry weight, spike dry weight and penultimate length had high genetic variability. Significant differences were observed among studied wheat genotypes. The results step wise regression and path analysis showed that harvest index, biological yield, penultimate dry weight, earliness and chlorophyll content exerted the high contributions on grain yield. Harvest index and biological yield had the greatest positive direct effects (0.82 and 0.44, respectively) on grain yield. Results of this study indicate the existence of high genetic diversity in Iranian landrace gene pools which can be useful in wheat improvement breeding program. In addition, some morpho-physiological traits such as harvest index, biological yield, peduncle and penultimate dry weights, chlorophyll content and earliness can be used as selection criteria for wheat yield improvement for drought stress conditions.

During grain development, appropriate water status of soil has key importance for starch accumulation in grains and hormone changes. For this, the study carried out on two Iranian wheat cultivars Pishtaz and Karaj3 in a factorial experiment based on randomized complete block design with three replications under irrigated and drought in a field experiment at research farm of Agriculture College, university of Tehran in Karaj. The aim of this research was to determine grain filling rate, carbohydrates content during different stages of grain filling, yield and its components. Results showed that Pishtaz cultivar in early grain-filling stages had high grain-filling rate, total soluble carbohydrate, sucrose, glucose and fructose in comparison to Karaj3 cultivar under irrigated and drought conditions. Indole-3-acetic acid (IAA) concentration of grains were high at the early stages of grain-filling, but Abscisic acid (ABA) concentration were high at the linear stages, which in this case Pishtaz was prevalent. Grain yield, biological yield, harvest index, 1000 kernel weight and number of kernels per spike in Pishtaz were higher than Karaj3 in two conditions. Results suggested that differences between cultivars in case of grain yield ant its component substantially resulted from variations of hormonal levels IAA, ABA and grain-filling rate.

This study was carried out to evaluate empirical models of competition, as two separated experiments based on a randomized complete block design with 3 replications at Agricultural Faculty of Bu-Ali Sina University, in 2008-2009. In both Experiments, Alvand and Sayson cultivar were planted with densities of 450 plants m-2. In the 1st experiment, feral rye (Secale cereale) with densities of 0, 20, 40, 60 and 80 plants m-2 were planted. In the 2nd experiment, wild mustard (Sinapis arvensis) density was 0, 8, 16, 24 and 32 plants m-2. The results showed that biological and grain yield of Sayson in interference with both weed species, were reduced more than Alvand. Wild mustard in evaluated density treatments showed more damage on wheat in compared to feral rye. Study of values observed and predicted of weed density, one and two parameter models of relative leaf area and relative dry weight indicated that two parameter models of relative leaf area and relative dry weight of both weed species was more appropriate factor to predict wheat yield loss.

In order to study the effects of organic and inorganic nitrogen sources on quantitative and qualitative characteristics of three winter rapeseed cultivars, a field experiment was carried out as factorial arrangement in complete block design with three replications in Agricultural and Natural Resources Research Center of Markazi Province, Arak, during 2008-2009 growing season. Three rapeseed cultivars (Okapi, Modena and Licord) and three sources of nitrogen (Azocompost, Urea and 50% Azocompos plus 50% Urea) comprised the experimental factors. Azocompost fertilizer was utilized before sowing time and urea fertilizer was applied at three stages inclodings of sowing time, stem elongation and before flowering. Results showed that rapeseed cultivars had significant differences for all traits. Licord cultivar had the highest seed yield, 1000-seed weight, seeds per silique in secondary branches, biological and oil yield. Also there was significant difference between nitrogen sources for all characteristics at 1% probability level. Integrated nitrogen treatment showed superiority to other treatments for siliques per secondary branches, siliques per main branch, biological yield, seed yield and oil yield. The interaction effect between nitrogen sources and rapeseed cultivars was significant for all traits at 1% probability level. Licord cultivar with integrated nitrogen treatment showed the highest biological yield, harvest index and seed yield.

This experiment was conducted to investigation of some agronomical traits in different castor bean genotypes at west Azarbaijan, in Agricultural Research Station of Urmia, as completely randomized block design with three replications, during 2007-2008. Result showed that the effect of different genotype were significant on all characteristics. The highest and lowest number of grain per plant observed in 80-11-1 (Shahreza) and 80-16-1 (Fasa) genotypes, respectively. The maximum 1000 grains weight (388.3 gr) observed in 80-29 genotype. Also, the highest seminals ear height from surface of ground (105.6 cm) observed at genotype of 80-4 and the lowest seminals ear height from surface of ground (27.3 cm) observed at genotype of 80-31. The greatest percent of pistil flower (91%) observed at genotype of 80-16-1. The highest grain yield and oil yield obtained at genotype of 80 -7. Therefore, if the purpose of planting this plant is achieving high economic performance, 80-7 genotype can be recommended for this area.