Nitrogen transformation in four Japanese soils following manure+urea amendment

Abstract

Understanding the effects of manure amendment on soil nitrogen (N) mineralization is crucial for a better assessment of N supplying potential of manure to maximize crop yield and minimize possible contamination of surface and belowground water resources. The effects of manure amendment on N mineralization were therefore studied under laboratory conditions. Surface (0–30 cm) samples of four Japanese soils: Andosol, red-yellow soil, masatsuchi, and sandune soil were each treated with chicken manure (PM), cattle manure (CM), swine manure (SM), ostrich manure (OM), and urea, and incubated for 8 weeks at 25°C. Nitrogen mineralization was studied in a 2 M KCl extract of samples collected at weekly intervals. The results showed that N mineralization was affected by both soil and manure types. NH4-N was found to be the dominant form of mineral N while appreciable increases in NO3 levels were observed during the 7th week. The rate of net N mineralization was highest in urea-treated soils, and the stimulating effect of urea on soil N mineralization was noted in the soils. Nitrogen mineralization from manure-treated soils was very low, suggesting that their N effect in the short-run should not be overvalued. In Andosol, CM and OM treatments exhibited negative N fertilizer effects. Ostrich and chicken manures showed high potentials for raising the pH of masatsuchi and sandune soils.