Investigations on the rôle of organic matter in plant nutrition. Part IX. Oxidation of organic matter in the soil and plant assimilation

Abstract

1. The organic carbon contents of a number of tropical soils (from India, Burma and Ceylon) were determined. It was found that most of them-including some which are reputed to be fertile-are poor in that constituent as compared with the soils of temperate regions. 2. When a manure is applied to a soil (under tropical conditions), the increased benefit to the crop is more due to the decomposition of the added material than to greater availability of the original organic matter of the soil. The carbon content is not a correct measure of the possible availability of a manure. Addition of minerals may increase or depress the beneficial effects that may be derived through application of organic manures. 3. Treatment with minute quantities of chemical oxidisers such as permanganate, hydrogen peroxide or ferric oxide helps to increase the availability of the organic matter of the soil. In the case of barley, the effect is best seen if the seeds are sown shortly after the treatment. In the course of three weeks, the dry weights of seedlings are increased by over 50 per cent. 4. It has been shown that plants receiving a useful supply of farmyard manure (10 tons) can grow, at any rate in the early stages, independent of atmospheric carbon dioxide. The dry weights of seedlings receiving CO₂-free air were of the same order as those receiving ordinary air. 5. The significance of the foregoing and other observations has been discussed.