احسان ربیعیان

The first factor limiting plant yield in many crop ecosystems is drought stress, and plant productivity under these conditions depends on the distribution of dry matter between plant organs and the spatial distribution of roots in the soil. Knowledge of root length conditions and its distribution in soil profile, which is an indicator of the ability of plants to absorb water from deeper layers and better root permeability in the soil, as well as understanding the shape of the root system, is important (Wasson et al., 2012). In general, the size, morphology, and architecture of the root system determine the plant's ability to absorb water and nutrients, as well as the relative size and growth rate of the shoot (Vamerali et al., 2003). Root growth is determined by the genetic characteristics of the plant as well as the physical and chemical characteristics of the soil. Even in wet areas in response to drought stress, root growth is limited to the topsoil, and when the soil dries, its infiltration resistance increases rapidly, resulting in a combination of drought stresses. Soil and its infiltration resistance (He et al., 2017). Reduction of root dry weight in rice (Nasiri et al., 2015), fresh weight of root in rapeseed (Razaviezadeh and Amoubeigi, 2013) indicate the negative effect of drought stress on root characteristics in Different plants. Tillage is the only crop method by which humans can directly affect soil properties. Moisture storage and aeration to the roots, depending on the desired or unfavorable application of tillage, affects the growth and development of plant roots and ultimately its yield (Bronick and Lal, 2005).

This experiment was conducted in split -split plots based on randomized complete block design with three replications. Tillage systems as the main -plot in two factors was including no tillage and conventional tillage, Water stress as the subplot in three levels by 30, 60 and 90 Percent of moisture requirement and nitrogen urea as the sub-sub plot at three levels by 0, 50 and 100 percent of the recommended rate.

The combined variance analyses indicated that the maximum root length (4147 cm per plant), root volume (158.13 cm3 per plant), root area (3055.7 cm2 per plant), root length density (0.44 cm2. cm-3), root dry weight (24.32 gr pl-1) and plant fresh weight (6732.6 gr. m-2) was obtained from the interaction of conventional tillage in mild drought stress (90% of the plant's water requirement) in 100% of the plant's nitrogen fertilizer requirement. Also, the interaction effect of severe drought stress (30% of plant water requirement) in 100% of plant nitrogen fertilizer requirement led to a sharp decrease in studied traits in both studied tillage systems. Although the conventional tillage system in this study ultimately increased the root growth characteristics and fresh weight of the forage maize plant, but because no significant difference in wet forage yield was observed in both studied tillage systems, the system no tillage is recommended because it can improve the physical and chemical properties of the soil in the long turn.

To evaluate the effects of micro-nutrients foliar application and plant density on two bean genotypes, an experiment was conducted in split factorial arrangement based on randomized complete block design with three replications at the research farm of College of Agriculture and Natural Resources, Tehran University in 2015. Foliar spraying in four levels (control (water), ferrous sulfate (2 g.L-1), zinc sulfate (2 g.L-1), and mixture of ferrous sulfate and zinc (2 g.L-1)) was the main factor and different levels of plant density (20, 30 and 40 plants per square meter) as well as two bean genotypes (varieties Akhtar and D81083 Line) were considered as sub-plot factors. The results showed that compared to control, foliar application increased 32.12 and 30.47% of grain yield in D81083 line and Akhtar cultivar, respectively. Simultaneous foliar application of iron and zinc micronutrient fertilizers significantly increased the studied traits in both genotypes. Akhtar cultivar did not show a significant difference in terms of grain yield between densities of 30 and 40 plants per square meter, but at the density of 30 plants per square meter, D81083 line had a higher yield than the other two densities. In general, the results showed that the highest grain yield was obtained from simultaneous foliar application of iron and zinc in D81083 line with a density of 30 plants per square meter.

Legumes contain an average of 18-32% protein and are an important source of protein for low-income people (Majnoun Hussein, 2008). Chickpea (Cicer arietinum L.) Is known for its resistance to moisture changes; this plant shows physiological and morphological changes under conditions of water scarcity (Ghorbanli et al., 2001). Chickpea grows in a wide range of weather conditions from the subtropical to Mediterranean regions of western Asia, northern Africa, and southern and southwestern Europe (Toker et al. 2007). Environmental stresses are the most important factor that limits crop production of chickpea. The most critical environmental stresses that have a negative effect on crop production are water and heat stresses (Rahbarian et al. 2011). By applying the effect of different levels of irrigation and plant density on yield and yield components of chickpea, grain yield, 1000-seed weight, the number of pods per plant and harvest index decreased during drought stress (Raei et al., 2008). Severe drought stress, by reducing the water uptake by the roots, disrupts the transfer of sap in the phloem, which ultimately leads to a decrease in nutrient uptake and the activity of antioxidant enzymes (Armand et al. 2016). Plant density is one of the most important management factors on crops that will affect plant yield. When competition for growth increases, the yield will be decreased. The selection of appropriate plant density should be based on environmental factors such as cultivar, cultivation target, weed competition, seed size, soil moisture content, and plant characteristics including plant height, plant density, leaf angle, and production capacity of the growing environment (Khajehpour, 2008). According to the above, this study was conducted to investigate the effects of different levels of irrigation and planting density on some agronomic traits of white chickpea in Karaj.

To investigate the effect of water regime and plant density on some agronomical traits of chickpea (Cicer arietinum), a split-plot experiment based on randomized complete block design with three replications conducted at the College of Agriculture and Natural Resources of Karaj, Iran in 2015. The water levels included eight levels (I1 =full irrigation at all growth stages, I2 = irrigation to grain filling and then stop, I3 = irrigation to podding and then stop, I4 = irrigation to flowering and then cut, I5 = 50% of full irrigation at all growth stages, I6 = 50% of full irrigation to grain filling and then stop, I7 = 50% of full irrigation to podding and then stop, I8 = 50% of full irrigation to flowering and then stop, considered as the main factor and plant density at three levels (30, 40 and 50 plants.m-1) as subplots. Geographical characteristics of this farm include 1321 meters above sea level, longitude 51 degrees east, latitude 35 degrees and 48 minutes north. This region has a hot and dry climate with an average rainfall of 33 years, about 248 mm.

The results showed that increasing water deficit stress reduced the growth traits and ultimately the grain yield of chickpea cultivar ILC 482. Increasing plant density increased the growth traits of yield components and grain yield. The highest grain yield (2892 kg. ha-1) was obtained in full irrigation (I1), and the lowest (1075 kg. ha-1) gained from I4. The highest grain yield (2068 kg. ha-1) was acquired at 40 plants m-1.

The results of this study showed that low water stress reduced the yield of chickpeas, but since Iran has low average rainfall, it is possible to achieve a good yield by using 50% irrigation at all stages of growth.

In order to investigate the effects of irrigation regime and plant density on agronomic and some physiological traits of chickpea (Cicer arietinum), a split-plot layout based on a randomized complete block design with three replications conducted at the research field of University of Tehtan (Karaj- Iran) in 2015-2016. The irrigation regime included eight levels (A1 =full irrigation at all growth stages, A2 = irrigation to grain filling and then cut, A3 = irrigation to podding and then cut, A4 = irrigation to flowering and then cut, A5 = low irrigation or 50% of full irrigation at all growth stages, A6 = 50% of full irrigation to grain filling and then cut, A7 = 50% of full irrigation to podding and then cut, A8 = 50% of full irrigation to flowering and then cut) and plant density at three levels (30, 40 and 50 plants.m-1) were considered as the main and subplots factor, respectively. The results showed that total chlorophyll and chlorophyll a, b, leaf area index, leaf relative water content, light use efficiency and seed yield were declined under water deficit but the light extinction coefficient and water use efficiency increased. The highest seed yield (2068 kg/ha) obtained from 40 plants.m-2. Also, under the low irrigation conditions, by applying 50% irrigation in all stages of chickpea growth the optimum yield can be produced.

Selenium is of micronutrients which beside its effective role on increment of endurance of plants such as rice against undesirable environmental effects، plays an important role in human health، due to its anti-oxidant and anti-cancer characteristics. Thus، to evaluate the influence of selenium on diminishing the negative effect of salinity and low seed storage in germination of Shafagh rice cultivar (CV. Shafagh) a factorial experiment was carried out based on completely randomized factorial design (CRFD) with three replications at the Physiology Lab of Shahid Chamran University in 2012. Testing factors included pretreatment of seeds with selenium in 0 and 16 mg/l، salinity in three levels including 0، 6، and 12 dS/m، and seed grain weight of 22، 24، and 26 gr. Results showed that salinity stress caused drastic and significant damage on measured properties of rice germination as much as 32 to 59 % in germination indices and 30-60% in germination characteristics. Priming with selenium rectified the salinity damage (1-23%) and low seed grain weight (32-47%) significantly، so that the germination rate in control treatment was classified in the same statistical group with selenium treatments and seed grain weight of 24 gr and also rice primed with selenium and salinity of 6 dS/m. Accordingly، salinity value and low seed weight had a drastic negative effect on all measured properties، but selenium pretreatment rectified the damages on germination through the increment of anti-oxidant enzymes.