Soybean and maize cultivation in South America: Environmental comparison of different cropping systems

Maize and soybean are two widely spread crops for food, feed and biofuel production, and in South America there are some of the most important producing countries in the world. This study investigates the environmental impact linked to their agricultural production in a sub-tropical South American context, starting from primary data relating to a cultivated area in eastern Paraguay. To this end, the Life Cycle Assessment approach was adopted in a cradle-to-farm gate perspective, evaluating eight different impact categories. In particular, two widespread intra-annual rotations were compared, both of which consider soybean as a first-season crop, alternating in the second-season with maize or soybean itself. Environmental results were expressed both in a crop-to-crop approach (per t of individual product) and with four different units expressing the land management function (1 ha year(-1)); the productive function (1 GJ ha(-1) year(-1) and 1 t of crude protein ha(-1) year(-1)) and finally the financial function (1 USD of gross margin ha(-1) year(-1)) of the two different cropping systems. In the cropping system approach, results expressed per hectare of cultivated area and per t of crude protein produced do not see one cropping system performing better than the other consistently over the evaluated impact categories. The soybean-maize rotation, on the other hand, appeared clearly more efficient from an environmental point of view in terms of gross energy and gross margin produced per hectare per year. The lack of a shared consensus on the most appropriate and comprehensive way to express the results of LCA studies on cropping systems makes difficult the selection of the best system. In particular, there are still on-going limitations and controversies in selecting the most appropriate functional unit for cropping systems LCA.