Abstract
Relationships between chemical composition and nitrogen mineralization characteristics of 14 brand samples of caged layer manures (free from secondary materials) on the market were examined to find simple and quick methods for evaluation of available nitrogen content in poultry manure. 1) Total nitrogen (T-N) content on dry matter basis of poultry manure in this investigation ranged 24-70 g kg^-1, C/N ratio 3.5-9.4, 0.1 M sodium hydroxide soluble nitrogen (Na-N) 8-45 g kg^-1, and inorganic nitrogen (Ino-N) 0.8-7.6 g kg^-1. 2) The absorption spectra of 0.1 M sodium pyrophosphate extract of poultry manure with low C/N ratio showed a maximum at around 290 nm which indicates the existence of uric acid. Uric acid nitrogen (UAN)^^^- content was tentatively estimated from the difference of absorbance between 290 and 260 nm, ΔA290-260 (equation 1). UAN^^^- content ranged 0-34 g kg^-1, and occupied up to 54% of T-N or 75% of Na-N. Sum of UAN^^^- and Ino-N correlated closely with Na-N and T-N. 3) Judging from the time course of nitrogen mineralization rate, available nitrogen from poultry manure was hypothetically divided into three categories, i.e., instantly available, earlier slow-release and later slow-release. Instantly available nitrogen content corresponded nearly to the sum of Ino-N and UAN^^^-, and also correlated closely with Na-N and T-N. Earlier slow-release nitrogen showed some significant correlations with these nitrogen components. However, no correlation was found between later slow-release nitrogen and any chemical components analyzed in this experiment. 4) Ino-N after 1 d incubation with soil at 30℃ had high correlations with Ino-N after longer incubation. 5) We could evaluate available nitrogen content in poultry manures by using any one of T-N, Na-N, UAN^^^-+Ino-N and Ino-N after 1 d incubation with soil at 30℃.
