a suitable soil plant available potassium extractant for a loess soil with illite dominance in clay fraction and the effects of azotobacter and vermicompost on wheat yield, potassium uptake and tissue concentration

the effects of an azotobacter chrococum isolate (strain ag11) and vermicompost and their combined effects on a rain-fed winter wheat (var. zagros) nutrient uptake and growth and soil water content were investigated with a farm trial.  the dry matter yield was determined in 5 occasions. gravimetric soil water content, soil microbial respiration and the number of azotobacter were determined at same occasions. grain yield and yield components were measured at harvest. soil nitrate and ammonium, potassium, phosphorous, calcium, magnesium, iron, zinc, copper, manganese and cadmium were determined before heading and at harvest. total nitrogen, potassium, phosphorous, calcium, magnesium, iron, zinc, copper and manganese were also determined for plant tissues before heading and at harvest and also for a representative vermicompost sample. treatments with azotobacter inoculation improved dry matter yield before heading, spikes per square meter, grain yield and straw. azotbacter increased root density and potassium availability in rhizosphere. vermicompost also increased grain yield. in addition to a low correlation with potassium uptake a high quantity of potassium is extracted by ammonium acetate relative to preset sufficiency levels which are misleading. maximum correlation with potassium uptake and yield were obtained by extraction with sodium tetra phenyl boron. soil water contents were not affected by any treatment.