Determination of total phosphorus in soil using simple Kjeldahl digestion

A Kjeldahl digestion method normally used for total nitrogen (N) was compared with NaOH fusion and dry ashing met:hods for determination of total phosphorus (P). Overall there was good correlation between the methods (r(2)=0.996). Results from the digestion method were on average 3.7% lower than the fusion and dry ashing methods, but there were significant differences between methods as shown by the regression analysis. The digestion method proved suitable for analysis of highly organic soils and some soils from the Pacific Islands. It was also useful for estimation of total P in well-weathered soils such as Oxisols and in A horizons, but not suitable for less weathered mineral soils.