Tropical forests account for between 20 and 25% of the world terrestrial carbon (C). Soils under tropical forest contain approximately the same amount of C as the lush vegetation above it. The current conversion of Amazonian forest to agricultural land makes disturbance of this C stock important to the global C balance and net greenhouse gas emissions. Changes in land use, particularly by clearing forests, reduce organic C by 20% to 50% in the upper soil layers. Furthermore, this reduction of soil organic matter (SOM) is causing soil degradation. Thus agriculture is not sustainable without nutrient inputs beyond 3 years of cultivation. The efficiency of conventional fertilizers (such as nitrogen (N)) is limited by a low nutrient retention capacity conjoined with strong tropical rains. On the other hand, large amounts of phosphate fertilizers are needed to overcome the soil’s high P-fixation capacity.