Threats and Recovery of Black Soils of Argentina: A Story with Surprises and Discoveries

Black Soils of Argentina are dominant in the Pampas region and are key to its economy because they support most of its grain production, and livestock for meat. When they were devoted to agriculture with conventional tillage with plows, they lost an important part of their organic carbon (30–60%) and their original fertility. Most farmers adopted no-till management more than three decades ago, focusing primarily on summer crops like soybeans and corn. No-till farming brought many advantages, such as improved water retention, reduced water evaporation, reduced soil erosion, and lower fuel and labor costs. However, instead of the anticipated increases in organic carbon, it generally stabilized and the soils began to show shallow compaction and the development of laminar structures with planar voids. Subsequent research linked these types of structures and lack of increases in organic carbon to the low return of carbon residues and the effect of agricultural machinery traffic, on soils that were not mechanically removed. Due to its predominantly silty loam texture, with 85–95% of fine silt fractions (2–20 μm) and little swelling clays (<2 μm), Pampas Black Soils lack natural macroporosity (pores greater than 100 μm) for root growth, and do not have the natural abiotic capacity to form these pores through microcracking. Research has shown that only through intensified crop rotations that increase carbon inputs to the soils, and reduced long fallow periods without living plants, for example by sowing more winter crops such as wheat, barley and winter cover crops such as vetch and oats, it is possible to improve soil carbon balances, create biopores, and allow soils to recover their friability and original structure. In the last 15 years about 15% of farmers adopted this better management practices, and soil quality of Black Soils could be recovered. The challenge is to expand these good practices to the rest of farmers.