Extended abstract
1- Introduction
Climatic conditions are considered as one of the key factors in the production of agricultural crops specially dry farming crops (Mohammadi, 2010). Temperature and precipitation are quantitative parameters. In addition, temporal and regional changes are the essential variables which determine a wide variety of thermal and humidity needs for a particular region. Almost all agro-climatic classifications include the above mentioned variables. The main purpose of this study is to recognize favorable and unfavorable zones for dry land wheat in Khorasan-e Razavi Province.
2- Methodolody
The region for this study is Khorasan-e Razavi Province with an area of 116493/39 square kilometers located between 33° and 52ˊ to 37° and 42ˊ latitude and 56° and 19ˊ to 61° and 16ˊ longitude in the northern hemosphere(Statistical Yearbook of Khorasan-e Razavi, 2009).
The research method is based upon a documentary – descriptive approach. The basis for selecting meteorological stations was the common statistical period of 20 years (1990 – 2010). In order to form a data bank, the available data was entered into Excel for 40 meteorological stations. To ensure the quality of the data as well as its homogeneity, a set of homogeneity tests and quality control of non-graphical data (run test) were performed. Furthermore, for reconstructing the data and creating auxuliary points for discovering isotherm and isoprecipitation area, the proportions and differences method (Alizadeh, 2011: 786) was used in addition to interpolation method using Krijing method. Then a computer program was designed in Microsoft Visual Studio in c#.Net 2005 which performed homogeneity test.
In the next stage, dry land wheat farming was dated considering the fact that wheat needs 5 millimeters precipitation in 5 centimeters cultivation depth in order to sprout. (Ehteramian, 2009: 39)
In order to set the dates of cultivation related to the selected stations, September 23rd was chosen as the base per annum and a ratio was assigned for each day. Then, the weighed values were arranged based on descending dates and the most appropriate datewass measured using Vibul formula with 75 percent of probability (Alizadeh, 2001). The Vibul Formula is as follows:

Where
P = Cultivation Date with 75 Percent Probability
m = Row Number
n = Number of Data
Furthermore, in order to set the date of different stages of growth, accumulative temperatures threshold was used. Annual precipitation is the most important climatic variable in dry land wheat farming. Wheat needs at least 250 to 300 millimeters precipitation during growth.
Considering the above-mentioned cases about annual rainfall and how they are distributed, the precipitation measured by the meteorological stations based on 250 millimeters rainfall and more with 75 percent probability, seasonal rainfall level and rainfall level in May with 75 percent probability, and also rainfall amount during sprouting, flowering and seed filling in the area were classified in GIS Environment.
3- Discussion
Regarding the mentioned indexes in setting date for wheat cultivation and also according to the initial precipitation date for 5 millimeters or more during 1 or 2 successive days with 75 percent probability, the date of initial rainfall and consequently that of cultivation were determined for the meteorological stations.
Since temperature is one of the vital factors in geo-botany and especially agricultural crops and there is a specified temperature threshold for each type of plant and owing to the fact that agricultural crops are deeply affected by tensions of low and high temperatures, this factor was analyzed during sensitive stages of the growth.
4- Conclusion and Suggestions
After providing the mentioned maps and compiling them in GIS Environment and also locating the regions which were not cultivable such as urban areas, salt marshes, pastures and regions with an elevation of more than 2500 meters, the final map for agro climatic zoning of Khorasan-e Razavi Province was prepared for dry land wheat farming.
In this map, 4 agro climatic zones are clearly visible, the details of which are as follows:
(1) Appropriate Regions: which have a relatively good potential for wheat production since the regions have appropriate climatic conditions. The area for this region is about 26 percent of the province.
(2) Medium Regions: these regions have a lower quality in climatic condition in comparison with the previous regions. The area for this region is about 21 percent of the province.
(3) Weak Regions: in these regions, dry land wheat farming potential is faced with several problems, the area of which is bout 24 percent of the province.
(4) Very Weak regions: n these regions, dry land wheat farming is not economical due to a lack of adequate rainfall and a rise in temperature. The area of this region is about 24 percent of the province. The area of this region is about 29 percent of the province.
Due to the climatic changes appeared in recent years, it is suggested that the models for cultivation be reassessed and the potentials and favorable agricultural lands for the crops which have never been taken into consideration found. Should Internal Meteorological Stations cover the province in the form of a regular network within the framework offered by World Meteorological Organization (WMO), the research projects can show better results.