Evaluating Agro-Climatologically Variables to Identify Suitable Areas for Rapeseed in Different Dates of Sowing by GIS approach

Abstract

The study carried out in tow provinces (Isfahan and Chaharmahal va Bakhtyiari), central and southwest, Iran. The study area covers approximately 37659 Km² of total area. This area is located between latitude 30° 42′ N and 33° 37′ N and between longitude 49° 56′ W and 51° 57′ W. The climate variables taken into account were maximum and minimum daily average temperature, Growth Degree Day (GDD) between four dates of sowing to physiological maturity and four dates sowing to freezing start day (rosette), monthly precipitation, monthly relative humidity (March to May) and number of freezing days. Climate variables and DEM data layers were prepared and suitability classes were determined, using simple limitation (SLA) purposed by modified of FAO method, were matched against specific winter oilseed rape (Brassica napus L.) requirements derived from agricultural experiments and literature review. The results indicated that the main limited factors are GDD from sowing to physiological maturity and sowing to freezing start day. The overlay maps for climate variables and DEM suitability evaluation using SLA identified 11.2% (sowing date: 20 August to 5 September), 12.5% (sowing date: 6 September to 20 September), 0.4% (sowing date: 21 September to 5 October) and 0.06% (sowing date: 6 October to 20 October) of the surface area land have suitable in study area.