Effect of straw,cellulose and lignin on the turnover and availability of labelled ammonium nitrate

Summary An experiment was carried out to investigate how straw, cellulose and lignin affect the turnover and availability of inorganic labelled N in soil. The experiment comprised an incubation period in which the soil was incubated with ¹⁵NH₄ ¹⁵NO₃ and organic materials followed by drying and by cropping the soil with Lolium perenne. The incubation period lasted 148 days during which soil samples were taken 36 and 148 days after the beginning of incubation. Addition of organic materials to the soil promoted the incorporation of inorganic N into organic matter and decreased apparent N denitrification losses during the first period of incubation (0–36 days after beginning of incubation). In this respect straw and cellulose were more effective than lignin. The organic materials also promoted the fixation of NH₄ ⁺ by clay minerals. In all treatments highest fixation of labelled NH₄ ⁺ by clay minerals was found at the end of the incubation period. During the cropping period high apparent denitrification losses were observed particularly in the straw and cellulose treatment. Hence the recovery of labelled N by Lolium was particularly low in these treatments while in the control treatment the ¹⁵N recovery was about twice as high.