Evaluation of Spatial Variation of Soil Fertility Quality and Its Relationship with Rice Yield in Paddy Fields of Kuchesfahan District, Guilan Province

Rice (Oryza sativa L.) is one of the strategic agricultural products of Iran. Recognizing the fertility status and quality of paddy soils is the effective factors on increasing rice yield. The aim of this study was to determine the quality of soil fertility and identify its limiting factors in paddy fields of Kuchesfahan District, Iran. For this purpose, before rice cultivation, a total of 130 composite soil samples with uniform geographical distribution were collected and prepared to measure some important physical and chemical properties affecting soil quality. Then, rice yield was measured in 70 locations. Principal component analysis and fuzzy logic were used to prepare the minimum effective data set and qualitative ranking of soil properties, respectively. After determining the soil quality index using the integrated algorithm, its relationship with rice yield was determined by statistical methods and spatial statistics using regression method. As the minimum effective data set, the total N, available P, K, Fe, percentages of clay and silt, and cation exchange capacity described 72% of the studied soil changes. Paddy fields in the western half of Kuchesfahan had more deficiency in total N and available P. These soils were also of lower fertility quality. Some of the lands located in the north and northeast of the study area had a soil quality index of more than 0.95 and were in the very fertile group. In these soils, the yield of rice was higher than other areas. The lowest yield of Hashemi cultivar was 3500 kg/ha in the southern half, and the highest yield was 5272 kg/ha in the eastern half of the study area. Due to deficiency of total N and available P in 36% and 50% of the studied lands, respectively, it is necessary that fertilizer application for these nutrients be site-specific and in proportion to their soil fertility status.