A wet oxidation procedure suitable for total nitrogen and phosphorus in soil

A wet oxidation digestion previously developed for plant material has now been evaluated for a range of British soil types. The traditional Kjeldahl procedure using sulphuric acid, salt and catalyst was modified to include hydrogen peroxide as an additional oxidant. The method is suitable for estimating both nitrogen and phosphorus in soil and overcomes the need for separate digestion procedures for these elements. It compared favourably with a normal Kjeldahl method for nitrogen and with a mixed acid oxidation system for phosphorus and recovery was complete after two hours. Total phosphorus and organic nitrogen were recovered together with labile ammonium‐nitrogen. Nitrate‐nitrogen would require a further modification and the recovery of ‘fixed’ lattice ammonium‐nitrogen was not assessed. Samples had to be finely ground to achieve good precision and recovery.