Critical limit for phosphorus in a Red Latosol of the Brazilian Cerrado

Successive applications of phosphate fertilisers can exceed the phosphorus (P) requirements of plants and soil, resultingin surface accumulation and loss to aquatic systems, and therefore require monitoring. The aim of this study was to determine amathematical model for the critical limit for phosphorus in the environment (CLPE) in a Red Latosol of the Cerrado, and to monitor theamount of P in the soil of 46 rural properties in the micro watershed of the Ribeirão Abóbora River. Sand was added to a dystroferricRed Latosol to simulate soils with textures of 10%, 20%, 30%, 40% and 50% clay, in order to quantify the maximum P adsorptioncapacity (MPAC) and determine the CLPE. Soil from 46 rural properties that make up the micro watershed of the Ribeirão AbóboraRiver was collected, and the P and clay content was determined. The MPAC decreased proportionally to the reduction in clay content.Th e estimating equation to determine the CLPE for the Red Latosol of the Cerrado is CLPE = 16.64 + 0.432* (% clay), which can besimplifi ed to CLPE = 20 + 0.5* (% clay). Th e P content on four of the properties in the micro watershed of the Ribeirão Abóbora Riveris greater than the CLPE. It is therefore recommended that the use of phosphate sources be suspended until appropriate P levels return,and that close attention be paid to these properties so that P values again reach acceptable levels, and no P is transferred to the water sources.