فصلنامه علوم زراعی ایران
سال هجدهم شماره 3 (پیاپی 71، پاییز 1395)

Global warming and climate change have created a serious changes in different regions all over the world including Iran. It has intensified drought stress and water shortage that negatively affect growth and development of crop plants including rice, and threats sustainable crop production and food security. As rice-based cropping systems mostly relied on growing irrigated-lowland rice in most of rice growing countries as well as Iran, which use large amounts of fresh water, therefore, there is a need to change the rice-based cropping systems as to use less water while mainting high productivity. Therefore, possibility for changing rice-based cropping systems from continuous irrigated system to aerobic, using aerobic rice genotypes, which have been developed for water-shortage conditions could be considered in Iran. Today, a improved aerobic rice genotypes have been developed with highergrain yield about 11 t.ha-1 and less than 50% water use as compared to the irrigated lowland cultivars. Research on development and growing of aerobic rice in Iran has showed that there is potential for growing such rice genotypes in water-shortage periods as well as in rotation with other winter crops in different areas that rice can be grown but water availability is limited. Therefore, in this review, we discuss the advantages of aerobic rice development and production in different countries including Iran.

Changes in environmental conditions have led to various types of stresses that affect plants growth, development, and also its survival. Since the growth regulators improve plant tolerance to unfavorable environmental conditions, therefore, y the effect of drought stress and foliar application of some growth regulatorson rapeseed cv. Hyola 401 was studied. A field experiment was carried out as split plot arrangements using randomized complete block design with three replications at Safiabad Agricultural Research Center, Dezful, Iran during 2012-2014. The main plots were assigned to three irrigation levels; irrigation after 70mm evaporation from evaporation pan as control treatment (Optimum irrigation), withholding irrigation at flowering and silique stages, and sub plots included 10 levels of foliar application (100, 200, 300 mg.l-1 ascorbic acid, 100, 200, 300 μmol; salisylic acid; 10, 20, 30 vol% methanol and distilled water as control treatment). Results showed that withholding irrigation at flowering and silique stages led to reduction in grain yield by 38% and 15%, respectively. The interaction of withholding irrigation × foliar application showed that the highest (4493 kg.ha-1) seed yield under optimum irrigation conditions belonged to foliar application of ascorbic acid (300 mg.l-1) and the lowest (1968 kg.ha-1) to withholding irrigation at flowering stage and foliar application of distilled water (control). Foliar application of ascorbic acid (300 mg.l-1) led to enhancement of seed yield under optimum irrigation conditions and withholding irrigation during the silique stage. By increasing drought stress severity chlorophylla decreased while chlorophyllb was enhanced. Effect of methanol (30%) on proline accumulation was more than ascorbic acid and salicylic acid under mild and severe drought stress conditions. It was concluded that application of growth regulators increased seed yield due to increase in proline and phytosynthetic pigments accumulation and their effect on seed yield components. Application of ascorbic acid (300 mg.l-1) under optimum irrigation and mild stress and methanol (30%) at severe stress conditions improved seed yield of rapeseed cv. Hayola 304.

Environmental and economic challenges resulting from the application of nitrogen fertilizers have increased concerns about its productivity in the agricultural systems. This study was conducted to evaluate SSM-Wheat model to simulate nitrogen budgeting with various nitrogen application scenarios (Dry land-without nitrogen, Dry land-low nitrogen, Irrigated-without nitrogen, Irrigated-conventional, Irrigated-high nitrogen and Irrigated-very high nitrogen) in rainfed and irrigated conditions in the wheat-based cropping systems of Gorgan region in Iran in a 21-years period (1990-2010). Results indicated that the average total losses of nitrogen were significantly different among different scenarios. In all scenarios, the proportion of nitrogen loss (81%), as gaseous was more than that of leaching (19%). Nitrogen loss by nitrification ranged between 5.9 and 59.2 kg.ha-1 with average 23.2 kg.ha-1 while nitrogen volatilization ranged between 0 and 14.9 kg.ha-1 with an average 5.8 kg.ha-1. Also, the maximum nitrogen leached was associated with irrigated wheat-high nitrogen scenario that had significant difference with other scenarios. However, the lowest amount observed in the rainfed wheat-without nitrogen scenario that had no significant difference with irrigated wheat-without nitrogen scenario. The highest productivity was observed in irrigated wheat-conventional scenarios (26 kg.kg-1) and irrigated wheat high nitrogen (25.9 kg.kg-1) which was significantly different than the other scenarios. Therefore, irrigated wheat- conventional scenario was identified as suitable scenario in wheat production in Gorgan, Iran, due to cost saving, low leaching, less environmental pollution, adequate irrigation and less fertilizer use.

Although role of salicylic acid (SA) in enhancement of salinity tolerance of plants has been well shown, more researches are needed for better understanding of its physiological mechanisms. In this experiment, the effect of different SA concentrations (0, 0.5, 1.0, 1.5 and 2.0 mM) was examined on biochemical attributes and grain yield of barley cv. Nosrat under non-saline and saline conditions (2 and 12 dS.m-1, respectively) during 2012-13 and 2013-14 growing seasons at the National Salinity Research Center, Yazd, Iran. Salt stress enhanced soluble proteins content, free proline, malondialdehyde and electrolyte leakage by 22.1%, 147.7%, 87.2% and 102.9%, respectively. However, membrane stability index as well as concentrations of chlorophyll a and b reduced by 33.2%, 31.4% and 59.3%, respectively. Salt stress also decreased grain yield by 34.2% and 40.9% in the first and second year, respectively. Salicylic acid reduced the negative effect of salt stress on grain yield, therefore, SA foliar application decreased the rate of grain yield reduction under saline condition from 42.1 in no-SA to 27.3% in 1.5 mM in the first year and from 43.7% in no-SA to 33.8% in 1.0 mM in the second year. This mitigation could be related to biochemical attributes, as SA at different concentration levels enhanced soluble proteins content, free proline, concentration of chlorophyll a and b and carotenoids as well as membrane stability index, and reduced malondialdehyde and electrolyte leakage. It can be concluded that SA had better effect up to 2.0 and 1.0 mM under non-saline and saline conditions, respectively. In Genral, SA with reducing negative impact of salt stress on biochemical attributes could improve salinity tolerance and increase grain yield of barely cv. Nosrat.

To determine appropriate ratio for intercropping of oat and berseem clover under manure application levels, a field experiment was carried out as split-plot arrangements using randomized complete block with three replications in 2015-2016 cropping season at Ramin Agricultural and Natural Resources University of Khuzestan, Ahvaz, Iran. Experimental treetments included: manure: 0, 12, 24, 36 ton.ha-1 from composted cow manure were assigned to main plots, and five ratio of oat mixed cropped with breseem clover: I: sole crop of oat, II: 75% oat 25% clover, III: 50% oat 50% clover, IV: 25% oat 75% clover, V: clover sole cropped were randomized in sub-plots. Results showed that the highest dry forage yield (12849 kg.ha-1) and crude protein yield (2404 kg.ha-1) obtained from 50 % oat 50 % clover and application of 36 ton.ha-1 of manure. The highest forage crude protein conten (%) and dry matter digestibility obtained from sole cropping of berseem clover and application of 36 ton.ha-1 of manure. The highest forage ash observed in 75% clover 25% oat and highest water soluble carbohydrate, NDF and ADF measured in sole cropping of oat. 50% oat 50% berseem clover with application of 36 ton.ha-1 of manure had the highest LER (1.53) as compared with other mixed cropping ratios.

To determine the relationship between grain yield and yield components and grouping of 150 F8 recombinant inbred lines derived from a cross between two Iranian rice varieties; Gharib and Sepidroud, a field experiment was conducted using Augmented design in the research field of Faculty of Agriculture, University of Guilan, Rasht, Iran, in 2013. Correlation coefficients showed positive and significant correlation between grain yield with number of panicle per plant, number of filled grain per panicle, number of spikelet per panicle and panicle length. Path coefficient analysis for grain yield also showed that maximum positive direct effect belonged to flag leaf length and number of panicle per plant that implies these traits are important characteristics associated with grain yield. These traits can be used as selction criteria for indirect selection for genetic improvement of grain yield in rice breeding programs in Iran. Rice recombinant inbred lines were classified in three distinct groups by cluster analysis using ward method with 94% confidence. Recombinat inbred lines in third cluster had higher tiller number per plant, panicle number per plant, panicle length, spikelet fertility, thousand grain weight, grain yield, RWC and chlorophyll content were identified as highly valuable sources to be incorporated in rice breeding programs. These lines can also be used for selection of high yielding cultivars with desirable traits.