Organic fertiliser-based agricultural management systems -- either manure or ploughed-in legumes -- have the same yields as conventional systems based on mineral fertiliser, preserve carbon and nitrogen in the soil, and could even contribute to the reduction of the amount of carbon dioxide in the atmosphere. This is the conclusion of a 15-year study of three distinct maize/soybean agroecosystems by Laurie E Drinkwater and colleagues from Rodale Institute in Pennsylvania, USA. Application of organic particles in the major maize/soybean growing region in the US would, say the researchers, sequester an amount of carbon equal to 1-2 per cent of the estimated annual carbon released into the atmosphere from fossil fuel combustion in the US. This is a significant contribution considering that the US has agreed to reduce its average carbon dioxide emissions to 7 per cent below the 1990 levels by 2008-2012 as part of the Kyoto Protocol, the researchers say. Further, organic systems need less energy to run than conventional systems, thus reducing carbon dioxide further.