Multiple constraints prevent smallholders from adopting fertilizers even with regional supply of agricultural inputs expanding and soils being worn-out. Few smallholders in the study completely replaced nutrients from vegetation with fertilizers. Instead, the authors found that a hybrid system that combines nutrients from vegetation and fertilizers was approximately twice as common as exclusive fertilizer use. We suggest that the option for this diversified “nutrient portfolio” may result not only from a lack of capital or knowledge regarding return on fertilizer use, but also from the need to adapt to the economic constraints facing smallholders and minimize risk.

Results indicate that a rural extension programme aimed at supporting a rapid and complete replacement of ashes from vegetation by fertilizers could prove unsuccessful for Amazonian smallholders.