Umsatz und Wirkung von Harnstoff‐Dicyandiamid‐ sowie Ammonsulfat‐Dicyandiamid‐Produkten zu Weidelgras und Reis

Abstract

Transformation and effect of urea – dicyandiamide and ammonium sulphate – dicyandiamide products with ryegrass and rice The transformation of urea or ammonium sulphate fertilizers both in combination with dicyandiamide was tested in soil under aerobic conditions. Nitrification was determined after percolation and different incubation periods by measuring the amount of nitrate leached. The mineralisation of urea and ammonium sulphate in the fertile soil was relatively quick. However the addition of 5 to 10 % DCD of the total fertilizer‐N inhibited vigorously the nitrification for 6 weeks, 20 % DCD even for 10 weeks. In this way the danger of nitrate leaching was greatly diminished and a slow and constant release of available nitrogen rendered. After a preceding aerobic incubation (up to 4 weeks), flooding and rice‐seeding diminished the nitrogen losses by leaching and denitrification remarkably in the Ha/DCD – as well as AS/DCD‐pots if compared to urea or ammonium sulphate alone. This effect was particulary clear after a 4 weeks incubation period. Therefore these urea – and ammonium sulphate‐dicy‐andiamide products guarantee a proper and constant N‐nutrition of the rice plants and may decrease the N‐losses caused by leaching and denitrification. Nitrogen fertilizers with nitrification inhibitors are of special interest for rice culture, because they allow a better timing of N‐fertilizer application, rice seeding and water flooding and render a more economical utilization of nitrogen fertilizers.