Soil was maintained in a moist condition with as complete aeration as possible, for periods up to 89 weeks, either alone or after the addition of straw, ground-up mustard plants, ground-up tare plants, or ammonium sulphate. The nitrogen which existed as nitrate, ammonia, or other materials soluble in cold water, as compounds only soluble in hot water, or as substances only soluble in dilute HCl, was determined at intervals during this period. In general, little change took place after 11 weeks apart from a very slow and very slight increase in the nitrate produced, except after the addition of straw. Ammonia was reduced to a trace in all cases. The whole of the nitrogen soluble in cold water became converted into nitrate or ammonia in less than 11 weeks, except in the case of the admixture with straw. With straw there was far less accumulation of nitrate than when no addition was made, and this prevention of the formation of nitrate continued to the end of the experiment (89 weeks). The less soluble nitrogenous material (i.e. that only soluble in hot water or in HCl) was hardly affected by the long incubation.

The added nitrogen was entirely recovered after the end of the experiment, except where ammonium sulphate was used. In this case there was an apparent disappearance of 30% of the added nitrogen.