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 among study results, sources of disagreement among results, 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 studies evaluating this topic from both agronomic and environmental perspectives, there are no quantitative summaries of the available data. Thus a meta-analysis has the potential to advance the understanding of this subject, and help address questions about P placement that are common to both the production agriculture and environmental communities.

The basic objectives of this study are to: 1) find, analyze, and summarize published and unpublished field-based data on corn and soybean response to P fertilizer placement and interaction with tillage, 2) complete a data review on yield response and P loss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. The methodology will involve a systematic review of published and unpublished research on P fertilizer placement under different tillage systems and diverse soils in the USA, with emphasis on the Midwest and Great Plains regions. Data collection will go back at least 30 years. The two response variables evaluated will be crop yield and P runoff loss.

A thorough literature search has been completed that included an original number of approximately 56,000 publications. This initial search included the main databases (Digital Library, ScienceDirect, WileyInterScience, SpringerLink, and Web of Science). Publications from “grey” literature were also included— primarily conference proceedings and research reports. After applying specific selection criteria, about 250 papers were selected and entered in a database for analysis. Statistical data analysis has been completed, and the final summary is under development. Publications and deliverables from the effort will be available in the coming weeks. This study was planned for one year of support.