MINERALIZATION OF NITROGEN AND CARBON IN SOILS AMENDED WITH COMPOSTED MANURE

A study was conducted under laboratory conditions to determine the quantity of N mineralized from four composted manures incorporated into 2.7 kg of St-Jude sand or Tilly silty loam at rates of 0.05%, 0.10% and 0.20% of total N. With one exception (a hog slurry-sawdust based compost), net cumulative mineralization of N (N(m)) during successive incubation periods increased with incubation time and with the rate of addition. After four months of incubation, N(m) values varied from 0 to 14% of total added N. A significant third order interaction on N(m) values was obatained with compost type, application rate and soil type. Net immobilization of N was apparent at all incorporation rates of hog slurry compost in the two soils. To evaluate C mineralization, composts were applied at the highest N rate and CO2 production measured periodically. One to 8.2% of total added C from manure composts was mineralized after 28 days of incubation. For each compost type, C mineralization was higher with the sandy than with the loamy mixtures. With composted sheep manure and immature cow manure compost, which contained the highest amounts of potentially mineralizable C, the highest application rate to sandy soil promoted loss of N.