Effect of storage and composting on the properties and degradability of cattle manure

Abstract Stockpiling or thermophilic composting of cattle manure resulted in significant carbon losses of 17% and 26.4% and relative nitrogen gains of 25% and 32.7% for stockpiled and composted manure, respectively. As a consequence, C/N ratios decreased with increasing time of storage or composting. However, neither the pH nor the mineral nitrogen and organic carbon contents of the 0–50 μm fractions were significant indicators of the transformations of these materials. The degradability of the manure was measured by incubation for 2 weeks in a brown calcareous soil, following 1 week of preincubation. The biodegradation index (BI) or the proportion of CO 2 released from the amended soil in relation to the control soil was calculated. The oldest manure materials obtained either by composting or stockpiling had BI of less than 1, the closest value to that of the unamended soil, whereas raw manure materials had the highest BI values. There was a direct relationship between BI values and C/N ratios. The kinetics of carbon and nitrogen mineralization of composted manure also confirmed differences between treatments. The CO 2 evolution followed logarithmic curves over 76 days of incubation with higher initial slopes for the raw manure materials and younger composted materials. Nitrogen mineralization was a mirror image of carbon mineralization with the exception of the oldest manure which had the lowest C/N ratio (12) and did not lead to nitrogen immobilization.