Decomposition of the organic materials from hill soils and pastures I.—Incubation method for studying the mineralisation of carbon, nitrogen and phosphorus

Plant materials and sheep faeces from 2 hill sites were used to develop a method suitable for measuring the production of CO2 and mineral N and P during incubation with aqueous soil extract. Variation in sample size (2 or 5 g) and source of the extract inoculum (from A0 or A1 soil horizon) had little effect on the results, but production of mineral N and P was reduced in the absence of any inoculum. Nitrogen was lost during incubation in both open and closed systems, but by absorption of evolved ammonia in 50% sulphuric acid almost complete recovery of nitrogen was achieved in the closed system. More NH3, nitrate‐N and CO2 were produced at 25% moisture‐holding capacity than at 100%, but variation in moisture content had little effect on ammonium‐N production. Lowering the incubation temperature resulted in reduced production of CO2 and mineral‐N and P, but sheep faeces produced most ammonium‐N at 10°.