Agroforestry strategies for alleviating soil chemical constraints to food and fiber production in the Brazilian Amazon.
Fernandes E.C.M. | Matos J.C. de Souza
The main soil chemical constraints on agricultural production systems in the Amazon include soil acidity, phosphorus (P) deficiency, and low effective cation exchange capacity (ECEC). About 80% of the Amazon has acid soils with pH values of less than 5.3 in the topsoil. Associated with soil acidity, is the problem of aluminum toxicity and phosphorus deficiency. The low soil ECEC of most Amazonian soils is also a major soil chemical constraint to plant productivity since the leaching of mobile nutrients (such as potassium) increases as ECEC decreases. Agroforestry systems have the potential to control erosion, maintain soil organic matter and soil physical properties, augment nitrogen fixation, and promote efficient cycling of the scarce nutrients in Amazonian soils. The rationale for supposing that agroforestry systems can alleviate the soil chemical constraints to food and fibre production is that the nutrient exports via the harvest of crop and animal products, erosion, leaching, volatilization, and the deterioration in soil physical properties due to cropping or grazing can be counteracted by the tree component via: 1) nutrient uptake by deep rooted trees allowing for capture and surface deposition via tree litter, of nutrients beyond the reach of crop roots (more efficient nutrient cycling), 2) increased amounts of organic (shoot and root) inputs to the soil help to maintain soil organic matter and thus improve soil structure and nutrient status, and 3) increased nutrient additions to the soil via nitrogen fixation.Show more [+] Less [-]