Land suitability evaluation of Golestan province for planting Pisum sativa based on climatic factors

The development and preservation of ecological balance will be achieved when used in accordance with land capabilities. By studying the factors affecting on products productivity, it is possible to plan with more comprehensive knowledge and provide appropriate facilities in accordance with the capabilities of the environment (Jafarbeyglou & Mobarak, 2008). Mostly, the systems under planting have low yields, which, in addition to management issues, the regional climate capacity is sometimes as limiting factor (Baniaghil, 2015). Pisum sativa is one of the legume family plants, which is important due to its short growth period, low nutrition needs and potential for nitrogen fixation. The agriculture lands of Golestan province are about 646.5 thousand hectare (32% of Province area). But not knowing of ecological needs and potential production of peas, non-suitable lands in Golestan province was allocated for peas planting; and this leads to non-reach to maximum production capacity and yield of a crop per unit area. Therefore, indicating advantages, strengths and weaknesses of the province can be a good guide for governmental and private investments in the region.

According to the geographical position, Golestan province is between 35 degrees and 47 minutes to 28 degrees and 8 minutes north latitude and 53 degrees and 10 minutes east of the Greenwich meridian. Golestan Province is located between Alborz Mountains, Turkmenistan's deserts, the mountains of North Khorasan and the Caspian Sea. In this study, climatic data (precipitation, maximum temperature, minimum temperature and optimum temperature) were obtained from 12-year (2013-2014), 4 synoptic stations and 21 climate stations in Golestan province. Isotherm and isopluvial maps in Arc map and by using interpolation method based on inverse distance (IDW) was prepared. After standardizing the factors (fuzzy) and weighing the layers, by using the weighted linear combination (WLC) method in the TerrSet software environment, optimum areas of peas planting were obtained. Finally, by integrating the maps, the overall zoning of the pea production at the province was obtained in the Arc map.

The minimum temperature map shows that in the geographical distribution of probability of suitable temperatures for emergence and growth period for peas, in the areas of central and northeastern regions are highly suitable. There was no difference in the suitable and not suitable regions for minimum temperature during the planting season and growth period. The maximum temperature map shows that in the geographical distribution of probability of suitable temperatures for emergence and growth period, the regions in the East, South-East and West parts of the province are less suitable. The geographic distribution of the probability of suitable temperatures during the emergence of a significant part of the province has been allocated, and only the margins of the province, which are located mostly in the southeast, south and southwest, are not suitable for emergence of the Peas. Based on the precipitation map of the geographical distribution, the probability of occurrence of suitable rain during the emergence period is limited to the northeast, southeast and a small part of the southern province. While the optimal distribution of precipitation for the growth period is limited to narrow areas that cover the province from the east to the south-east. The results of the analysis of the paired comparisons between the climatic factors affecting planting of peas showed that, the precipitation during emergence and growing season was the highest with the coefficient of 0.289 and 0.220 respectively, and the minimum temperature of planting and growth period was 0.036 and 0.046, the lowest coefficients in the ranking earned. Land suitability of the province showed that 26.02% of the total area of the province is highly suitable and 48.42% is suitable. Generally, the climate of northeastern lands and eastern margins has suitable conditions for the planting of peas.

According to the results of this research, a large area of the central lands, the north and east of Golestan province according to climatic factors are not limiting for planting peas. But some of the land in center, marginal the southeast, southwest and northwest of the province are not suitable for the planting of this crop.