Compost type effects on nitrogen leaching from Inceptisol, Ultisol, and Andisol in a column experiment

Purpose: To more efficiently utilize composts as N sources while minimizing the environmental impact, it is necessary to understand the effects of compost type on N mobility in compost-amended soil with different characteristics. The objectives of this study are to investigate the effects of livestock manure composts on N leaching from soils and to identify the principal physicochemical variables of the composts that affect N leaching. Materials and methods: A combination leaching-incubation experiment using seven livestock manure composts and three soils (Inceptisol, Ultisol, and Andisol) with different characteristics was conducted for 19 weeks. Leachates were collected periodically and analyzed for various forms of N (NH₄⁺, NO₃^-, organic N, and total N). The effects of compost type on N leaching were assessed by analysis of variance and correlation between N leaching amounts and compost variables (pH, total C, total N, C/N, and various forms of extractable N). Results and discussion: Initial flush of N leaching at the first leaching event conducted after 1-week incubation was observed probably due to mineralization of readily decomposable N pool; the amount of N leached at 1-week incubation accounted for more than 50% of cumulative amount of N leached through 19-week incubation. Among the various compost variables tested, only total N concentration of compost was significantly (P<0.05) correlated with total N and mineral N (NH₄⁺ +NO₃^-) leached across all three soils, indicating that total N concentration of composts is the common factor affecting N leaching from the compost-amended soils. Comparing amongst the three soils, the cumulative amount of total N leached increased in the order of Andisol (34.5 to 103.4 mg N)>Ultisol (33.9 to 64.7 mg N) > Inceptisol (12.8 to 31.7 mg N) being affected by soil N availability. Conclusions: The significant effects of compost and soil types suggested that not only soils but also composts characteristics needs to be considered when establishing the compost application guidelines. Particularly when compost characteristics are considered, total N rather than the mineral N concentration of composts can be used to predict the N leaching potential in composts-amended soils.