The birth of a new cropping system: towards sustainability in the subtropical lowland agriculture

Developing cropping systems that meet multiple demands of high production, resource-use efficiency and low ecological footprint is a major global challenge. In Southern Brazilian lowlands, irrigated rice (Otyza sativa L.) in combination with fallow for beef production is the dominant cropping system. This system is key to Brazilian food security but faces problems of resource use efficiency, soil preservation and greenhouse gas emissions typically associated to rice irrigation. In this research, a multi-criteria analysis of the usual rice-fallow system, and a number of alternative production Schemes - i.e., the more recent rice-soybean (Glycine max (L.) Merr.) rotations and the newly developed systems based on large ridges, was made. The latter is based on the construction of large ridges (8 m width) on which rainfed maize (Zea mays L.) and soybean, conducted in no-tillage, are integrated with either beef-livestock production or cover crops in winter. This study was done in an experiment that lasted for nine years. The five cropping systems were managed as independent fields and a range of indicators related to crop management, productivity and sustainability was measured. The Rice-Fallow system required the lowest amount of energy, but it had the lowest energy use efficiency and highest carbon-based environmental footprints, when expressed as greenhouse gasses emitted per kg of food produced. The rice soybean rotation system presented an improved performance for the carbon-based footprints in comparison to the rice-fallow system. Within rice-soybean rotation, using minimum-tillage instead conventional tillage increased the overall carbon balance and the carbon sequestered into the soil as organic matter. Most strikingly, the new ridge-based systems exhibited the most favourable values for many of the indicators. The more diverse rotation system, and particularly the extension of the growing season to winter, resulted in improvements in soil quality, biomass production and carbon sequestration into the soil. Water- and light- use efficiency were increased, whereas greenhouse gas emissions reduced. The ridge-based crop-livestock integration offered the best balance between food production and environmental preservation. This cropping system is potentially one of best alternatives to increase agricultural diversification and sustainability in the sub-tropical lowlands such as in southern Brazil. This shows that modifications of cropping systems can result in major simultaneous improvements in yield, resource-use efficiency and ecological sustainability.