Phosphorus Runoff from Surface-Applied Fertilizer in Soil Trays and Comparison with Release in Batch and Soil Diffusion Assays.

Loss of phosphorus (P) through runoff from agricultural fields has been directly linked to eutrophication, a major water quality issue. The use of rainfall simulators is well accepted by scientists as a useful tool to quantify the loss of P in surface runoff. However, the methodology is time consuming, very laborious and costly given the apparatus and analyses involved, limiting the number of treatments which can be evaluated. In order to develop a rapid, inexpensive, and efficient screening process for the evaluation of new and environmentally friendly fertilizer technologies, we compared laboratory-scale methods to assess fertilizer formulations for: (i) nutrient release characteristics; (ii) nutrient diffusion in soil and (iii) P in runoff using rainfall simulators with indoor soil boxes. The release characteristic of different P fertilizer formulations was obtained in batch experiments based on electrical conductivity (EC) measurements. A Petri dish method with a fertilizer granule added in the centre was used to assess the P diffusion through a recently developed rapid visualization technique. Two rain simulators were built to assess nutrient runoff from the formulations; a regular size (3 x 3 x 2.5m) and a miniaturized version for laboratory-scale (1 x 0.6 x 1m) assessments. Grass was grown in the soil trays to create a vegetative coverage prior to application of different types of P fertilizers. The artificial rainfall delivered on the 5%-inclined trays generated the runoff, which was collected at regular intervals. The laboratory-based methods on nutrient release rate from fertilizers and the subsequent diffusion in the soil correlated well with the losses of P obtained in both rain simulator trials. The faster and inexpensive EC and diffusion visualization methodologies were good predictors of the risks of P losses in runoff and seem to be a useful tool for research on fertilizer-related losses of P from fertilized soils.