مكان‌يابي مناسب‌ترين مناطق كشت گندم ديم(مطالعه موردي: استان خراسان شمالي)

Locating the Most Suitable Dry Land Wheat Areas (Case Study: North Khorasan Province)

با توجه به اهميت عوامل اقليمي در توليد محصولات كشاورزي ديم و نيز توانايي‌هاي بالقوه استان خراسان شمالي، پهنه بندي اقليمي كشت گندم ديم در اين استان هدف اصلي اين تحقيق قرار گرفت. براي اين منظور از آمار بلندمدت 17 ايستگاه باران سنجي،اقليم‌شناسي، سينوپتيك، 5 ايستگاه تبخيرسنجي داخل استان و 6 ايستگاه سينوپتيك در خارج از اين استان جهت هم پوشاني بهتر استفاده شد. در اين تحقيق با توجه به تاريخ آغاز بارش‌هاي پاييزي براي هر منطقه از استان تاريخ كاشتي پيشنهاد شد. سپس مراحل مختلف رشد گندم ديم بر اساس محاسبه درجه روزهاي رشد (GDD) مراحل مختلف بدست آمد. در مرحله بعد، احتمال وقوع بارش سالانه 300 ميلي متر و بيشتر، مقادير بارش پاييزه، بهاره و خرداد با احتمال وقوع 75% بررسي شد. همچنين احتمال وقوع دماي مناسب جوانه زني گندم ديم، دماي حداكثر 25 و 30 درجه سانتي گراد در مرحله گل دهي و مرحله پرشدن دانه محاسبه گرديد. سپس با بهره گيري از نيازهاي رويشي (شرايط اقليمي مطلوب) گندم ديم، لايه هاي اطلاعاتي تهيه و كلاسه بندي شده و ارزش وزني هر كدام از پهنه ها مشخص شد. در نهايت با تلفيق نقشه ها در محيط GIS نقشه پهنه بندي اقليمي كشت گندم ديم در استان خراسان شمالي استخراج گرديد. اين نقشه نشان داد كه مناسبترين مناطق كشت گندم ديم در قسمتهاي شمال استان مي‌باشد و مناطق ضعيف در جنوب غربي و جنوب شرقي استان واقعند. همچنين اين تحقيق نشان داد كه با انطباق لايه هاي موثر در فرآيند كشت گندم ديم در محيط GIS، امكان شناخت مناطق مستعد كشت براي اين گياه زراعي وجود دارد.

Introduction Since, wheat is one of the most important and strategic crops in Iran, determining appropriate areas for planting dry land wheat, according to the heat, humidity and climate capabilities in different regions of Iran, can increase the yield of this crop. In this research, the climatic potential and their adaptation with the requirements of dry land wheat (autumn wheat) are determined in North Khorasan province. Materials and Methods The region in question is North Khorasan Province that located in North East of Iran. In this study, longterm data of 17 rain gage, climatology and synoptic stations, 5 evaporation stations inside the province and 6 synoptic stations outside of the province during 19862005 were used in order to overlap better. The exact date of various growth stages of wheat in the different parts of this province is calculated by growing degree days (GDD) according to the following equation (Behnia, 1376):  Where GDD is growing degree days, Tmax and Tmin are maximum and minimum daily temperatures (Celsius degree) respectively, Tb is the base temperature (Celsius degree), a and b are the beginning and the end of date of phenological stage, respectively. The base temperature is the lowest temperature that is assumed to be no lower than the growth. The thermal units required for this crop are as follows: The total thermal units from sowing to sprout                                              180 GDD The total thermal units from sowing to flowering period                 1300 GDD The total thermal units from sowing to grain filling period              2100 GDD Discussion In this research, GIS is used for data analysis and processes. Then, by using growth requirements dry land wheat (optimum conditions), the data layers were classified and the weight of each zone was determined. Finally, by overlapping the maps in GIS, the dry land wheat climatic zoning map is prepared in North Khorasan. According to scientific references and climate conditions of study region, after determining the parameters for each of the stations and transferring them to GIS, four classes for each of the layers are defined (Table 1). In addition, for overlapping the layers according to climate conditions for planting dry land wheat and expert idea, the layers should have the same time scales, so the weight of each zone is assigned by a number from 0 to 100 (Table 2). By overlapping method (weight classes), all of the layers in table 2 are combined in GIS and finally land zoning map for dry land wheat is prepared in this province.     Table 1: Defined classes for each layer Qualitative Value Climate Parameters Unsuitable weak Moderate Suitable Rainfall probability 3000 mm and more (%) < 30 3050 5070 > 70 Autumn rainfall amounts (mm) < 80 85120 120155 > 155 Spring rainfall amounts (mm) < 125 125150 150190 > 190 June rainfall amounts (mm) < 20 2035 3550 > 50 Suitable temperatures probability for germination (%) < 50 5060 6070 > 70 Temperatures probability 25 ºC and more during flowering stage > 50 3750 2537 < 25 Temperatures probability 30 ºC and more during grain filling stage > 50 3750 2537 < 25 Temperatures probability 9 ºC and lower during flowering stage > 35 2535 1520 < 15 Temperatures probability 9 ºC and lower during grain filling stage > 35 2535 1525 < 15   Table 2: Weight of each class   Annual Rainfall Autumn Rainfall Spring Rainfall June Rainfall Sprouting Stage Temperature Flowering Stage Temperature Grain Filling Stage Temperature Unsuitable 20 30 25 15 90 90 weak 50 55 55 50 65 70 70 Moderate 75 80 70 65 75 50 50 Suitable 95 100 90 85 90 25 25 Results Appropriate Lands: because of suitable climate conditions during the growing period of wheat, they have high yield. This area is 6263 Km2 (22% of the area province) and it is allocated in the northeast and northwest until the west of this province. SemiAppropriate Lands: they are poorer than appropriate lands. Planting dry land wheat in this area is suggested and it can increase the yield of this crop. This area is 17534 Km2 (62% of the area province). 3. Weak Lands: these lands have low climate potential for planting dry land wheat. These regions are in the southeast and southwest of the province and they have lower annual rainfall and limited temperature in flowering and grain filling stages. This area is 4884 Km2 (16% of the area province) that are included Jajarm and Mangoli stations.