Multivariate Statistical Analysis of Potassium Status in Agricultural Soils in Hamadan, Western Iran

Multivariate statistical technique was used to determine the potassium (K+) status and to assess soil fertility and K leaching potential in some calcareous soils. Water-soluble K+ (H2O-K) and ammonium acetate-extractable K+ (NH4OAc-K) ranged from 0.019 to 0.590 (mean value 0.095) and 0.390 to 3.320 (mean value 0.954) cmolc kg−1, respectively. The nitric acid-extractable K+ (HNO3-K) varied from 1.03 to 13.63 (mean value 5.37) cmolc kg−1. The proportion of H2O-K ranged from 0.34% to 14.8% of HNO3-K, and 2.2% to 53.2% of NH4OAc-K. The proportion of NH4OAc-K ranged from 5.8% to 80% of HNO3-K (mean value 23% of HNO3-K). The tendency of the soil to lose K+ by leaching was examined by determining K+-Ca2+ exchange isotherms. The soils mostly had moderate to high values of K+ sorption capacity, ranging from 10% to 58% (mean value 28%) of added K+. The Gapon coefficient varied widely from 1.1 to 12.0 (L mol−1)−1/2. Clay minerals were dominated by illite, smectites and vermiculite with small amounts of kaolinite. Principal component analysis (PCA) showed that the first four components accounted for 27.7%, 21.4%, 13.8%, and 8.9% of total variation, respectively. The non-hierarchical cluster analysis (k-means clustering) grouped 75 sampling sites into six clusters, based on the similarity of soil quality characteristics. The results suggested that such classes could form a basis for variable-rate application to maintain an adequate K+ status for crop production and to reduce potential K+ loss from soil by leaching.