Evaluation of phosphorus management strategies for variable landscapes in Ontario

The potential of site-specific management of crop nutrients to improve fertilizer use efficiency and reduce environmental concerns has resulted in it being adopted by some farmers. This technology has been implemented; however, before a sound scientific basis for varying rates was available. Studies were conducted to determine the feasibility of site-specific management of phosphorus (P) fertilizer in Ontario and to determine if better placement of P fertilizer may be a more viable method of improving P fertilizer use. Analysis of 25 grid soil sampled (30 m spacing) farm fields in Ontario indicated that soil samples are required at a grid size of less than 30 m (or 11 times as many samples than are currently being taken) to adequately map its variability. In other studies it was found that in areas of limited variability in factors other than soil test P (STP) levels, the STP level was a good indicator of the probability of crop response. However, over the ambient variability found in two study fields, that had a medium STP level on average, yield and yield response to applied P fertilizer was not related to STP level. In studies that compared seed-placed to side-banded P fertilizer alone or in combination with each other it was found that unlike previous studies there was no benefit of seed-placed over side-banded P. There did appear to be an advantage of combining the two treatments. A visual analysis of P response data indicated that the response patterns differed between the two years of the study. To help researchers with future experiments to evaluate the spatial-temporal stability of crop yield a computational model was developed to give an unbiased estimate of the spatial temporal stability of yield. In general it was concluded that site-specific management of P had little potential in Ontario on soils of medium or greater STP level; but further experimentation is required to determine if spatial-temporal patterns of yield can be used to predict management zones in a field and if soils of lower in STP levels have a greater potential for variable management.