Phosphorus is a chemical element considered key to water quality, mainly acting as a trigger of algal blooms. The main source of phosphorus in small rural basins is agriculture practiced in the slopes of the basins. This phosphorus can come in various forms to the water body, but the most striking ones are the total and dissolved reactive phosphorus. The dissolved form has higher risks, because it can cover distances comparatively larger than the reactive phosphorus in suspension which can be deposited along the path. This study sought to determine if different coverage of annual crops can interfere in the transport of these forms of phosphorus, affecting the risk of degradation of water resources of small rural watersheds. Although there was no significant difference between treatments, but seasonality was verified along the experiment representing a growing season. This means that there was also some variation in the level of risk, since, in the first third of the first rains, the risk of entrainment of phosphorus in runoff was higher in relation to rainy periods more distant from the planting/fertilization period, making possible to assess the risk to the watershed in a seasonal way rather than annual.
small rural watersheds; management of the agricultural environment; contaminants from agricultural sources
