Characterization and potential nutrient value of on-farm and industrial composts

An understanding of the chemical factors that affect compost nutrient relea se is essential to adequately predict their contribution to plant nutrition . A laboratory experiment was conducted to characterize 23 on-farm and 6 in dustrial composts from Quebec (Canada) and to determine their N and P relea se pattern to an Arago sandy loam (Humo-Ferric Podzol), incubated in glass jars at 35 degreesC for 13 weeks. Regression analysis with all materials re vealed that the compost organic N mineralized after 13 wk was best predicte d by the percentage of compost N as humic substances, and NO3- and NH4+ con tents, whereas the P released was related to the soil-compost Mehlich-3 P c ontent at the beginning of the incubation and compost total P content. Regr ession analysis with the dairy manure group (n=15) yielded better predictio n of the amounts of N and P released. The same parameters as for the whole group were retained in that restricted analysis. This study indicates that the short-term N and P potential nutrient value of composts are dependent u pon compost source materials and manure management. The prediction of their nutrient release, especially N, would be improved if provided according to material source.