Increasing global demand for oil seeds and cereals during the past 50 years has caused an expansion in the cultivated areas and resulted in major soil management and crop production changes throughout Bolivia, Paraguay, Uruguay, Argentina and southern Brazil. Unprecedented adoption of no-tillage as well as improved soil fertility and plant genetics have increased yields, but the use of purchased inputs, monocropping i.e., continuous soybean (Glycine max (L.) Merr.), and marginal land cultivation have also increased. These changes have significantly altered the global food and feed supply role of these countries, but they have also resulted in various levels of soil degradation through wind and water erosion, soil compaction, soil organic matter (SOM) depletion, and nutrient losses. Sustainability is dependent upon local interactions between soil, climate, landscape characteristics, and production systems. This review examines the region’s current soil and crop conditions and summarizes several research studies designed to reduce or prevent soil degradation. Although the region has both environmental and soil resources that can sustain current agricultural production levels, increasing population, greater urbanization, and more available income will continue to increase the pressure on South American croplands. A better understanding of regional soil differences and quantifying potential consequences of current production practices on various soil resources is needed to ensure that scientific, educational, and regulatory programs result in land management recommendations that support intensification of agriculture without additional soil degradation or other unintended environmental consequences.

The Santa Lucia River basin provides drinking water to 60% of Uruguay population. The input of excessive amounts of nitrogen and phosphorus both from point and nonpoint sources could impair surface water quality and prevent its use for human consumption. The objective of this work was to evaluate surface water quality in small catchments under agricultural use located within this river basin. To this end, 5 streams and 4 small polders were surveyed between September 2008 and December 2009. The median concentrations of total phosphorus and total nitrogen in the streams across all sites and periods were 770 and 1659 µg L ⁻¹ , respectively, exceeding in the case of total phosphorus national and international thresholds. Furthermore, soluble phosphorous, the most readily available form to algae, represented 88.3% of total phosphorus. Concentrations of phosphorous and nitrogen in polders were also high. The eutrophication process of this water bodies could be linked to the intensive agricultural land use in the area because the nutrient input from cities and industries was not relevant in these catchments.

Crotalaria spectabilis and Crotalaria juncea are cover crops (CC) that are used in many different regions. Among the main attributes of these species are their high potential for biomass production and biological fixation of nitrogen (BNF). Attempting to maximize these attributes, while minimizing water consumption through high transpiration efficiency (TE), is a challenge in the design of sustainable agricultural rotations. In this study, the relationship between biomass productivity, BNF, and TE in C. spectabilis and C. juncea was evaluated. For this purpose, an experiment was carried out under controlled conditions without water limitations and using non-inoculated soil. BNF was determined by the natural abundance of ¹⁵N, while TE was estimated by several different methods, such as gravimetric or isotopic method (¹³C). C. juncea produced 42% less dry matter, fixed 28% less nitrogen from the air, and had 20% less TE than C. spectabilis. TE results in both species were consistent across methodologies. Under simulated environmental conditions of high temperature and non-limiting soil water content, C. spectabilis was a relatively more promising species than C. juncea to be used as CC.