Effects of Soil Nitrogen, Phosphorus and Potassium on Distribution of Rangeland Species, Weeds and Sustainability of Species in Khalat Poshan Rangelands of Tabriz County

Rangelands as natural ecosystems are consisted of enormous resources of genetic resources and plant species diversity. This diversity implies the rangeland stability against biotic and abiotic factors. In relation to the management of ecosystems، including rangeland ecosystems can be stated that sustainable management of their، is required to identification and assessment of spatial and temporal in its properties in order to optimal and sustainable utilization of resources. In order to study the effects of soil nutrients including Nitrogen (N)، Phosphorus (P) and Potassium (K) on dominant rangeland species and weeds distribution in Khalat Poshan rangelands of Tabriz County، fields experiment was conducted using grid sampling and the intersection lines between 20×40 m in 14 ha during 2012 spring. Canonical Correspondence Analysis (CCA) was used to examine the relationship between NPK of soil and rangeland species distribution. In the analysis that was done، the first two CCA axes explained 85% of the variation in 18 dominant rangeland species distribution. The first axis had negative correlation with nitrogen and potassium content in the soil and had positive correlation with phosphorus content، while the second axis showed positively correlation with all three of these elements. Two species of bulbous bluegrass (Poa bulbosa L.) and scariola (Scariola orientalis (Boiss.) Sojak) had highest correlation with phosphorus content of soil، whereas the sainfoin (Onobrichis atropatana Boiss) of the plants that had negative correlation with phosphorus content of soil. salsify (Tragopogon kotsschys Boiss) and trigonella (Trigonella fischeriana Ser.) had highest correlation with potassium content of soil. Between the nutrients studied، the highest correlation was observed between soil nitrogen and potassium. In general it can be said that poverty، lack or imbalance of nitrogen، phosphorus and potassium are essential elements required by plants in rangeland، there by reducing of the useful and palatable pasture species and increased of invasive species and non palatable and the rangeland sustainability will afoul threat of serious injury. Therefore، the sustainable management palatable species of rangelands constant attention is necessary to the balance of NPK in rangelands soil.