2.3. NPK determination in soil
In a drip irrigation system the injected nutrients through fertigation follow water moisture distribution in soil. Therefore, the soil samples were collected from two different locations: under the dipper and from the middle distance between dippers in order to represent the NPK distribution around the tree. The soil samples were collected from 0 to 50 cm soil layer. The samples were air dried and sieved with a 2 mm sieve then, subjected to chemical analysis. Total nitrogen was determined according to the Kjeldahl method (Jackson, 1973) using K jeltec auto 1030 analyzer.Available P was determined as described by Olsen and Somme's(1982) using ammonium molybdate colorimetric methods. Avail-able K was determined as described in Carson (1980) using flame emission spectrophotometer.