Meta-analysis of Phosphorus Fertilizer Placement and Tillage Interaction for Corn and Soybean in the U.S.

Meta-analysis uses statistical methods for combining results from multiple studies on a specific topic with the aim of identifying patterns, sources of disagreement, or other relationships that may exist among study results. Simply put, meta-analysis can be thought of as "conducting research about previous research" (after Wikipedia, 2015).

Phosphorus fertilizer placement and interactions with tillage have been studied extensively in corn-soybean systems in the USA. Results generally suggest that placement of P fertilizer can play an important role in plant uptake of P and crop yield, as well as potential P loss to surface water. Although there have been many individual studies evaluating this topic, there are no quantitative summaries of the available data. Thus a meta-analysis has the potential to advance the understanding of this subject. The basic objectives of this study are to: 1) find, analyze, and summarize published and unpublished field-based data on corn and soybean response to P fertilizer placement and interaction with tillage, 2) complete a data review on yield response and P loss with surface runoff as affected by P fertilizer placement and tillage interactions, and 3) include data reviews of estimated P use efficiency and economic return.

This meta-analysis involved a database search for all publications that included yield data for corn and soybean, and was conducted within Wiley International Science, Springer Link, Web of Science, Science Direct, and ACSESS Digital Library databases. The primary search criteria was set to include publications from 1980 to the present, and studies conducted in the Midwest or Great Plains region of the USA. The initial literature search yielded approximately 56,000 publications, including those from the “grey” literature. After applying specific selection criteria, the total number of papers suitable for this analysis was winnowed to 247. Studies from 11 states were included in the final total. The dataset was analyzed based on tillage and P fertilizer placement, with exclusion of P fertilizer rates <40 lb P₂O₅/A.

Results showed overall lower yields for no-till. Yields with band-placed P were generally lower than broadcast; however, the difference was statistically significant for only the no-till systems. The preliminary analysis for different soil test categories showed generally higher yields for broadcast application at lower soil test P levels. The investigators suggested that further improvements in data stewardship are needed to increase access and improve the use of published data. This was the final year of support for this project.