Soil organic matter fractionation and carbon mineralization under long-term manure application

Abstract:

A farmer once remarked that manure is nature’s savings account for soil carbon-but how much of what you deposit actually stays in the bank? This research examined soil organic matter fractionation and carbon mineralization rates under 12 years of continuous cattle manure application at three rates (5, 10, and 20 t ha⁻¹ yr⁻¹) compared with an unfertilized control in a wheat-maize rotation at the Escuela Nacional de Agricultura Tropical, Bucaramanga, Colombia. Soil samples from 0-15 and 15-30 cm depths were fractionated into light fraction, particulate organic matter, mineral-associated organic matter, and humin. Total SOC increased from 14.84 g kg⁻¹ (control) to 25.65 g kg⁻¹ (20 t ha⁻¹) in the 0-15 cm layer. The light fraction showed the largest proportional response (+129.7% at 20 t). Carbon mineralization (56-day incubation) was 38.4% higher under 20 t manure than the control. A carbon balance showed net annual SOC gain of 1,420 kg C ha⁻¹ at the 20 t rate. These results quantify the carbon sequestration potential of long-term manure application in tropical Andean soils.