Fertility Status of Paddy Soils in Guilan Province

Rational use of fertilizers in soil depends on the awareness of the condition of fertility and nutrient in soil. One approach is based on a comprehensive understanding and correct use of precision agriculture of agricultural soils. Thus the map of spatial variability of soil properties is a key step in the application of precision agriculture which based on the map, application of agricultural inputs could be managed in a systematic way. To this end, comprehensive study of paddy soils fertility in Guilan province through GIS mapping were counducted. Soil characters including Total N, P, K, pH, EC, OC and clay were measured in 8567 soil samples collected from arable land of Guilan province. These characters were analyzed through descriptive statistics, geostatistics and GIS. Mapping showed that most soils of the province in terms of pH and EC were favorable for the growth of rice plants, while total nitrogen, potassium and phosphorus need to be managed. Many paddy fields in the Central Plains area of Guilan and in the alluvial soils of Sepeedrud basin showed nitrogen deficiency which soil response to nitrogen fertilizer is high. In nearly 40% of the land surface, P concentration is less than critical level because of the continued cultivation of plants without use of phosphate fertilizers by farmers or the low ability of soil to preserve native soil phosphorus. Agricultural land of Guilan province was divided into Eastern and Western parts based on potassium content. In the most part of western area, available potassium is low, while in the eastern part, available potassium was higher than western part because of Sepeedrud sediment. In nearly 68% of the study area available potassium of soil was less than critical level(160 mg per kg) for growing cultivated Rice. The results in general showed that the nutrient status of paddy fields is not distributed uniformly from geographical point of view .Therefore, to prevent soil fertility decline and increase of production cost fertilizer distribution in the region and consumption of fertilizer in the field should be based on achieved results.