Temporal Complementarity of Soil P Pools In a Model Sustainable Agroecosystem.

The underlying P biogeochemical mechanisms of a model sustainable agroecosystem developed by researchers in North Florida Research and Education Center, University of Florida were investigated. The Sod Based Rotation SBR system is comprised of a 4 yr rotation system that is based on the concept of ‘temporal complementarity’ and involves 2 years of perennial grasses to build soil nutritive pools followed by a year of legumes and a year of cash crop to make use of the nutritive build up. This system has been shown to improve soil health, sequestering soil carbon while providing impressive economic benefits by minimizing nutrient, pesticide and water inputs; thereby increasing financial returns by 3 to 7 fold. We hypothesized that P uptake and cycling in this model system were complementary over period and the nutrient bioavailability would be reflected in the changes in P pools with the rotation components. The SBR was compared with a conventional rotation of Peanut and Cotton using a series of quick tests and a modified P fractionation scheme. Phosphorus fractionation studies indicated that readily available P ranged from 0.1-1.41 mg kg^-1 while bicarbonate extractable P pool ranged from 0.8-9.6 mg kg^-1. Average Mehlich-3 P, Bray-Kurtz and Mehich-1 values were 54, 43 and 33 mg kg^-1.  The extremely low values of exchangeable P, slightly higher values of bicarbonate available P, and higher values of double acid extractable P indicate differential P acquiring mechanisms to be potentially important. Overall mean exchangeable P values were greater in conventional system (4.6 mg kg^-1) than that of the SBR (3.4 mg kg^-1) indicating the distribution of nutrients through the entire rotation by perennial grasses between different P pools.