Estimation of carbon allocation to the roots from soil respiration measurements of oil palm

CO2 flux from the soil was measured in situ under oil palms in southern Benin. The experimental design took into account the spatial variability of the root density, the organic matter in the soil-palm agrosystem and the effect of factors such as the soil temperature and moisture. Measurements of CO2 release in situ, and a comparison with the results obtained in the laboratory from the same soil free of roots, provided an estimation of the roots contribution to the total CO2 flux. The instantaneous values for total release in situ were between 3.2 and 10.0 mu mol CO2 m(-2) s(-1). For frond pile zones rich in organic matter, and around oil palm trunks, root respiration accounted for 30% of the efflux when the soil was at field capacity and 80% when the soil was dry with a pF close to 4.2. This proportion remained constant in interrow zones at around 75%, irrespective of soil moisture. Subsequently carbon allocation to the roots was determined. Total CO2 release over a year was 57 Mg of CO2 ha(-1) yr(-1) (around 1610 g of C per m(2) per year), and carbon allocation to the roots was approximately 53 Mg of CO2 ha(-1) yr(-1) of which approximately 13 Mg CO2 ha(-1) yr(-1) (25%) was devoted to turn-over and 40 Mg CO2 ha(-1) yr(-1) (75%) to respiration.