Effect of composting on nutrient loss and nitrogen availability of cattle deep litter

Nitrogen and carbon emissions and plant nutrient leaching during storage of solid deep litter from dairy cow houses was examined in this study. Included was an assessment of the potential for reducing emission and leaching losses by compaction, mixing and by covering the deep litter. During a composting period of 132 days from October 1998 to March 1999, emissions of NH3, N2O and CH4 and leaching of nutrients during composting were measured. Denitrification was estimated as N unaccounted for in N mass balance calculations. During mixing of the deep litter, N was lost and the emission and leaching losses during composting were consequently low compared with the other treatments. Covering the compost with a porous tarpaulin or compacting the compost reduced emission losses to 12¯18% of total-N compared with a loss of 28% during composting of untreated deep litter. Most of the nitrogen loss was due to NH3 volatilization; leaching accounted for about one fifth of the N losses and only a little N was lost due to denitrification. Leaching loss of potassium (K) was 8¯16% of the amount present at the start of the experiment; compaction and a cover reduced the volume of liquid leaching from the heaps and K loss. Less than 0.3% of the total-N was emitted as N2O, and CH4 emission was between 0.01 and 0.03% of the C in the stored deep litter. The yield level of barley was poor in this study and the fertilizer effect of compost was low. The yield response of barley showed that compost had a significantly lower fertilizer efficiency than deep litter applied to the field directly after emptying the animal house.