N-mineralization in polyphenol-rich plant residues and their effect on nitrification of applied ammonium sulphate

Soil was incubated under greenhouse conditions with plant residues having varying phenolic and nitrogen contents. The total plant material added in staggered applications every 4 months was 15 g kg^?1 soil and the total incubation period was 12 months.The N-mineralization in these plant residues as influenced by their phenol and N contents was examined. The nitrification of applied (NH₄)₂SO₄ in these amended soils was also investigated under optimum conditions of pH.A high plant-N content resulted in increased N-mineralization of plant residue, but this effect was lowered by the presence of high concentrations of polyphenols in the decomposing residue, most probably due to increased participation of N with polyphenols in the formation of humus fractions.Soils amended with phenol-rich residues did not show any inhibition of nitrification of applied (NH₄)₂SO₄. Possible reasons are discussed. In organic matter decomposition, the quality of the leaf polyphenols appears to determine the degree of inhibition to soil nitrification.