Innovative Technology for Water Quality Protection in Agroforestry Systemswca2014-1246 Vimala Nair 1,*PKR Nair 1Rosa Mosquera-Losada 2Gerard-Alain Michel 1David Howlett 3Peter Nkedi-Kizza 1 1University of Florida, Gainesville, FL, United States, 2Universidad de Santiago de Compostela , Lugo, Spain, 3Division of Forestry, Carson City, Nevada, United States
Phosphorus saturation ratio (PSR) and soil phosphorus storage capacity (SPSC) are two concepts that have become popular related to phosphorus (P) chemistry and management of many agricultural soils in the United States and other parts of the world during the past two decades. The PSR is the molar ratio of phosphorus to iron and aluminum in an oxalate or a soil test solution such as Mehlich 3, and SPSC signifies the amount of P that can safely be stored within a soil prior to it becoming an environmental risk. The SPSC can be calculated based on a threshold PSR value, above which P release from the soil will increase substantially. In this study we evaluated the potential for using the PSR/SPSC concept to agroforestry and related land-use systems for identifying soils where P could pose a potential environmental threat. Studies were conducted on tree-based agricultural systems on different soil types: Alfisols (Quercus suber silvopasture; Extremadura Spain), Inceptisols (Pinus radiata and Betula alba silvopasture; Galicia, Spain), Spodosols (Pinus elliottii silvopasture; Manatee county, Florida), Oxisols (Uganda; Coffea canephora and Coffea arabica plantations), and Ultisols (Pinus elliottii silvopasture; Suwannee county, Florida). At all locations, PSR and SPSC were calculated for soils sampled by depth up to one-meter depth in most cases. Results showed that irrespective of soil type, P release from the soil increased once the threshold PSR value was reached. The P release generally decreased down a soil profile with the P storage capacity increasing deeper in a soil profile in a tree-based system compared to adjacent treeless plots. This is attributed to the ability of trees to remove of excess P (and other nutrients) from agricultural soils. The study suggests that the threshold PSR and SPSC could be used to predict P storage and loss from agricultural and agroforestry systems.