Agroforestry as an approach to minimizing nutrient loss from heavily fertilized soils: The Florida experience

Abstract

Nutrient buildup in the soil caused by increased animal manure and fertilizer use in agricultural and forestry practices may increase the potential for their loss from the soil, leading to groundwater contamination and nonpoint source pollution. Studies in the tropics have suggested that agroforestry practices can reduce such nutrient (especially nitrogen) losses because of enhanced nutrient uptake by tree and crop roots from varying soil depths, compared to more localized and shallow rooting depths of sole crop stands. In temperate systems, such benefits have been well documented for riparian forest buffer practices. Currently, other temperate agroforestry practices are also being considered for their potential to reduce runoff and leaching of chemicals and thereby improve environmental quality within the agricultural landscape. In this regard, the ‘Florida P-Index,’ which considers both phosphorus transport characteristics and management practices, may be a useful tool in the evaluation of nutrient management practices and environmental benefits of agroforestry. Preliminary results from an alleycropping site and a silvopastoral site on two different soil types in Florida suggest that both of these agroforestry practices will likely reduce nutrient loss compared to conventional agricultural practices. The primary aspects of P-Index include consideration of transport factors such as soil erosion, soil runoff class, leaching potential, and distance from a water body along with management factors such as soil test P, P application method, and source and rate of P application. P-Index evaluation of these studies indicates that both agroforestry sites can be on a nitrogen-based nutrient management program. The relevance of some management practices such as application of manure vs. inorganic fertilizer is also discussed in light of the P-Index and the two agroforestry practices.