Organic farming recycles local plant residues and compost to fertilize soils, whereas conventional agriculture uses mineral fertilizers that are mined then transported over long-distances. Therefore organic farming should emit less greenhouse gases. However the lower yields of organic farming may compromise the emission balance on a product basis. Agronomists Aguilera et al. observed that emissions from herbaceous crops in Spain were lower under organic farming both on an area basis and on a product basis, with the exception of rice due to higher methane emissions.