Determination of critical levels of phosphorus and potassium in under ground winter wheat soils in Varamin plain

Use of chemical fertilizers in Iran in past years were unbalance. In management of chemical fertilizers most attention was given to N and P fertilizers and K application was neglected. Unbalance use of chemical fertilizers caused to appear many problems that most important of them is unbalance levels of nutrients in soils. For example luxury consumption of P fertilizer was caused to concentrate of P in soils, in the other hands K was depleted in soils caused to lack of k application by farmers, thus the level of available K in soils in many farms is less than K critical levels. Twenty research farms were selected in dominant soil Seri at underground winter wheat to determine critical level of P and K with aim of optimize consumption of chemical fertilizers. The level of average K and P in farms was ranged from low to high. An experiment was conducted in each farm with three replication and RCBD design and four treatments as P0K0, P1K0, P0K1 and P1KI.P1 and K1 were 100 Kg/ha P2O5 as triple super phosphate and 100 Kg/ha K2O as potassium sulphate. Critical levels of P and K in soils were determined by Cate-Nelson method. These values were 8 and 270 mg/kg for P and K respectivly. By this way, 45 percent of soils underground wheat was deficient to P and 40 percent of them was deficient to K.