Essai de valorisation agricole de déchets industriels contenant de l'azote nitreux et nitrique

Abstract

10-15% oxidized inorganic N, half of which was in nitrite form, were used as N source for wheat and maize crops. In laboratory incubation the conversion of nitrite to nitrate varied from 22-52 mg N.kg soil -1 wk -1 at temperatures of 10, 15 and 20 °C in soil with a neutral pH. In acid soil at least one-third of the nitrite N was lost by chemical denitrification and the functioning of part of the microflora appeared to be perturbed: there was an increased mineralization of C and production of ammonia. In the field, the rate of conversion corresponded with laboratory results when the waste was applied as a solution, but halved with solid products. Persistance of nitrite in the soil was a function of the dose added. Application to wheat at the beginning of stem elongation slightly reduced grain yield (-5%), with nitrites slowing down N assimilation of the plants. Applied to maize at sowing, germination was strongly affected by nitrites, resulting in a diminution of grain yield which reached 30% depending on the application dose.When soil temperature had attained 10 °C, an application of 50 kg.ha -1 of oxidized N to the growing crop (wheat) allowed the 2 batches of waste to be used in agriculture.