عنوان مقاله [English]
Climate is a major environmental factor that controls all aspects of life. Among the climatic elements temperature is the important factor and because of this, study the effects of temperature on the growth of organisms, especially plants will be necessary. If temperature to be below the critical level of growth, plant growing stages will be stop and may hurt plant. The critical level temperature is different and dependent on the kind of plants. The majority of biological changes in plants is dependent on Growing Degree-days. In the present study, it has been achieved Growing Degree Days (GDD) Zoning with using temperature indicators. According to these factors, it has been determined capabilities and limitations of agricultural climate in different plant species adaption in country. Wheat is one of the strategic agricultural products of Iran. This variety of wheat has the best yield and quality in north-western provinces of country, including West and East Azerbaijan, Ardabil, Zanjan, Kordestan and Hamedan. Despite the fact that the mentioned region has the area of 17578000 acres or nearly 16.3% of the country area, the area under cultivation of winter wheat in these provinces consist about 40% of total wheat cultivating farms in the country or about 2411000 acres. This implies that the region is prone of cultivating wheat (and also other agricultural products) about 2.3 times more than other parts of country.
Another fact that verifies this is fraction of area under cultivation of wheat per total province area. Among 31 Iranian provinces, ranking of this statistic shows that all the provinces in selected area rank below 10, including first rank in country, Hamedan Province with 21.2% of its area under cultivation of wheat, Second rank Ardabil Province with 20.0%, rank 4 Kordestan province with 18.4%, rank 6 Zanjan provinces with 14.1% and finally, rank 9 and 10 East and West Azerbaijan provinces with 9.7% and 9.6% respectively.
Although the most important source of impact on yield of wheat, especially in dry farming, is adequate and timely precipitation, the climate change and global warming plays an undeniable role on long-term trends and attitudes toward choice of new places for building farms to answer the consistently increasing demand for this strategic product.
The trend in four phenological stages beside total Lenth of Crop Season (LCS) as a measure of intensity of the effect of climate is calculated in 27 stations in the region.
Materials and methods
For this research, it has been used daily temperature at 27 Synoptic Stations during 1981 to 2010 periods. For calculating heat units, it was used the thresholds of 5 and 10 ° C as the lower threshold and 30 and 35 C °for the upper thresholds. For determining of hit units, at first, the dates of starting and end of 5 and 10 C° temperatures were extracted and then heat units during the growing season was calculated from mean daily temperature minus the base temperature and zoning heat units maps in GIS were prepared.
Result and discussion
According to this research, the growing season length of 5 and 10 C° were divided into five categories in Iran. In the research, the areas of the country that Thermal Units based on 5 and 10 were homogeneous had taken in a group. Heat units in the base of 5 C° are divided into five groups, including 2000-2500, 2500-3000, 3000-3500, 3500-4000, 4000> (GDD) and for 10 C° are divided into four group including 500-1500, 1500-2500, 2500-3500, 3000>.(GDD).
Growing Season Degree-Days for the basis of 5 and 10 C° are declining from South to North and East to West in the country. The Heat Units amounts during the growing season at 5 C° are increased from South to North and West to East. These amounts are decreased from South to North for the base temperature 10 C° and are increasing from West to East. According to the obtained results, it can be suggested that in areas where the growing season is reducing, farmers by reducing crop yield and also products that have not been well face. That is better farmers used early growing plants until they got heat energy to supply in the plant during the growing season.