A COMPARATIVE STUDY OF SOME METHODS USED FOR ASSESSING THE AVAILABILITY OF N, P AND KIN SOILS

Abstract

The current research work was carried out to assess some methods used to estimate the available N, P and K in a wide range of different soil types in Egypt representing most Egyptian governorates (105 samples) to assign the most reliable method to assess the availability of these nutrients. The N availability was evaluated by using three different extractants, i.e. K-sulphate 1%, for soluble N03-N and Nl!t-N, acetic acid 10 % (Bray method), for oluble N03-N and acidified NaC110 %, for exchangeable Nl!t-N. The P extractants used to assess P availability were: Olsen (0.5 N NaHC03, pH 8.5), AB-DTPA, neutral AAc (1N), and adjusted-pH water (ADW) at pH 7.0, 8.0 or 8.5 and SER 1:1, 1:2 and 1:5 with each pH value. The K availability was assessed by using ;neutral AAc, AB-DTPA and ADW extractants that mentioned above. The study was also conducted with the purpose of comparing the efficiency of the ADW as an easy and simple extractant with the standard methods used for P and K extraction. Finally, the correlatiops between the extractable N, P and K and the uptake of these nutrients by barley plants grown on the studied soils were evaluated in a greenhouse experiment using simple correlation and stepwise regression analyses.