Influence of composting conditions on plant nutrient concentrations in manure compost

The objective was to compare the changes in the forms of nitrogen (N), potsssium (K), calcium (Ca), magnesium (Mg), and sodium (Na) during aerobic and anaerobic composting. Total N decreased during aerobic composting, but it increased from 3 to about 4% under anaerobic conditions, because of the absence of any losses in the form of ammonia and concentration effects due to a reduction in volume. Ammonium-N (NH4-N) was the dominant inorganic N fraction, but the level fell below the maximum value of 400 mg/kg for a mature compost after 77d of aerobic composting. Total and exchangeable Na levels under anaerobic conditions exceeded those under aerobic conditions by 15 and 11%; the total Mg in anaerobic compost also exceeded that in aerobic compost by 33%. Mean levels of exchangeable Ca under aerobic conditions were 12% greater than that under anaerobic conditions. Sodium concentration generally increased with time of composting, while the K content decreased with time under aerobic conditions. For Na and K, about 80% of the total content was in exchangeable form. The results also showed that about 85% of total Ca and 90% of total Mg in the composted manure were bound in organic fractions, as their presence in available form was relatively low. The mean value of electrical conductivity (EC) under aerobic condition exceeded that for anaerobic condition by 8%.