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Changes in bean-production practices by farmers cultivating steep lands in Costa Rica have impacted on agroecosystem sustainability. Frijol espeque, an input-based, land-use intensive, dibble-stick-planted, bean-growing method, was introduced to replace frijol tapado, a broadcast-planted traditional, low-labor, shifting agricultural practice. Socioeconomic impacts of the transition were assessed based on farmer surveys. Agronomic impacts of the transition were determined using on-farm experiments.
Frijol espeque produced significantly higher yields but lower returns on investment compared to frijol tapado. Clear-field and burned-field land preparation practices, used in frijol espeque, resulted in soil degradation as indicated by significantly greater soil losses due to erosion, depletion of plant nutrients, and increased soil bulk density. Soil erosion was controlled, aggregate stability maintained, and plant nutrients conserved in the mulch-based frijol tapado system.
Frijol espeque and frijol tapado were compared with labranza cero, an intermediary bean production method. Labranza cero is planted in straight rows using a dibble-stick, similar to frijol espeque, but has cut, fallow growth retained on the soil surface as a mulch, similar to frijol tapado. Labranza cero produced similar yields to clear-field frijol espeque while controlling soil degradation to an extent similar to frijol tapado.
Farmers have decreased the use of fallow rotations due to land-use competition. Increasing land-use intensity resulted in significantly decreased phosphorus availability, increased erosion, increased weed and web blight infestation, and decreased yields. For labranza cero, crop residues alone provided an insufficient mulch layer to decrease soil erosion losses, weed regrowth, or web blight infestation. Use of a grass fallow, in combination with mulch-based frijol espeque, controlled soil erosion and increased the availability of nitrogen and phosphorus for plant uptake.
Both agronomic and sociopolitical factors are responsible for the decreasing sustainability of bean production on steep lands in Costa Rica. Agricultural development programs need to address and assess the impacts of farmer adaptations of introduced technologies and changing land-use practices on agroecosystem sustainability and equity within the society. Assessment methods based on a combination of modified stability analyses and ANOVA were shown to be effective in evaluating both the productivity and the sustainability of the agroecosystem.