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Precipitation and temperature are two main climatic factors that influence crop productivity in arid and semi-arid areas. Study of the variability in these variables is thus important especially under dryland farming. In the present study, we evaluated the relationship between minimum, maximum, and mean temperatures; precipitation; and dryland wheat yield in northwest of Iran. The association between long-term weather data and dryland wheat yield for the time period bracketing 1990 and 2004 was investigated in seven stations (Ahar, Tabriz, Maragheh, Myaneh, Urmia, Khoy, and Makou) homogenously distributed over the study region. Aridity index (AI) was also calculated and its relationship with wheat yield was studied. Results showed that AI significantly decreased in the whole region (except for Urmia) with the highest variation in Maragheh and Myaneh. Increase in temperature was the major contributing factor to the increasing AI. Association between weather variables and dryland wheat yield at annual, seasonal, and monthly scales showed different results. At seasonal scale, spring was the main season affecting wheat yield. Also, at monthly scale, January, April, and May had more important role in wheat yield variation compared to the other months. The association between dryland wheat yield and weather variables was stronger in Maragheh and Myaneh. At the end, it was concluded that wheat yield was more affected by the variability in the climate in East Azerbaijan compared to that in West Azerbaijan. [ABSTRACT FROM AUTHOR]

Climate variability adversely impacts crop production and imposes a major constraint on farming planning, mostly under rainfed conditions, across the world. Considering the recent advances in climate science, many studies are trying to provide a reliable basis for climate, and subsequently agricultural production, forecasts. The El Niño-Southern Oscillation phenomenon (ENSO) is one of the principle sources of interannual climatic variability. In Iran, primarily in the northeast, rainfed cereal yield shows a high annual variability. This study investigated the role played by precipitation, temperature and three climate indices [Arctic Oscillation (AO), North Atlantic Oscillation (NAO) and NINO 3.4] in historically observed rainfed crop yields (1983-2005) of both barley and wheat in the northeast of Iran. The results revealed differences in the association between crop yield and climatic factors at different locations. The south of the study area is a very hot location, and the maximum temperature proved to be the limiting and determining factor for crop yields; temperature variability resulted in crop yield variability. For the north of the study area, NINO 3.4 exhibited a clear association trend with crop yields. In central locations, NAO provided a solid basis for the relationship between crop yields and climate factors. [ABSTRACT FROM AUTHOR]

Silicon (Si) can mitigate the deleterious impacts of various types of stresses on field crops. However, the potential of nano-silicon (nano-Si) in improving water stress and the relevant mechanisms remain unclear. Therefore, here, we examined the combined impacts of nano-Si and various irrigation regimes on antioxidant systems, osmolytes, photosynthesis-related parameters, and growth of sugar beet in a field trial. Treatments included three supplemental irrigation rates (I1, I2, and I3) arranged based on the crop evapotranspiration (100% ETC, 75% ETC, and 50% ETC) and three doses of nano-Si: 0, 1, and 2 mM. Irrigation regime treatments were performed at the six-to eight-leaf stage (49 days after sowing), which continued until the harvest (180 days after sowing). Water stress brought about a detrimental impact on the sugar beet growth, the relative water content of leaves (LRWC), leaf area index (LAI), and photosynthetic performance. In contrast, Water deficiency enhanced hydrogen peroxide (H2O2) and malondialdehyde (MDA) contents, which were followed by increasing antioxidant activities and osmolytes. Supplementation of nano-Si at low dose (1 mM) significantly increased chlorophyll contents, net photosynthesis (PN), glycine betaine (GB), flavonols (quercetin and rutin), and enzymatic antioxidants (superoxide dismutase, catalase, and guaiacol peroxidase). Furthermore, nano-Si at low dose (1 mM) decreased the amount of H2O2 and MDA. Instead, the higher dose (2 mM) of nano-Si exerted toxic effects on severe water-stressed (50% ETC) plants. The parallel increase in MDA and proline contents in sugar beet plants treated with two mM nano-Si along with severe water stress supports the view that proline augmentation presumably is a sign of stress injury instead of stress resistance. Overall, our results imply that nano-Si can play a protecting role in sugar beet plants during water stress by enhancing antioxidants, GB, and flavonols (quercetin and rutin). However, the concentration of nano-Si must be chosen with care. [ABSTRACT FROM AUTHOR]