Ammonium Production in Soil under Waterlogged Conditions as an Index of Nitrogen Availability

Abstract

MANY methods of obtaining an index of the availability of soil nitrogen to plants have been proposed, but it is generally accepted that the most satisfactory methods currently available are those involving estimation of the mineral nitrogen formed when soil is incubated under conditions which promote mineralization of the organic forms of soil nitrogen by soil micro-organisms^1,2. Numerous incubation techniques have been used for estimation of mineralizable soil nitrogen, but methods involving determination of the nitrate produced by incubation under aerobic conditions at 28°–35° C for 2–4 weeks have been generally preferred². However, recent work has shown that these nitrate-product ion methods are open to serious criticisms, and that the total mineral nitrogen produced during incubation should be determined². Also, the use of aerobic incubation techniques is complicated by problems in establishment and maintenance of satisfactory conditions of incubation^1,2. In an attempt to eliminate these problems and to develop an incubation method of estimating mineralizable nitrogen that is suitable for routine analysis of soils, we have investigated the possibility that methods involving estimation of the ammonium produced by incubation of soil under waterlogged conditions may provide an index of nitrogen availability. This investigation led to development of the following method of assessing mineralizable soil nitrogen: