Corn and Soybean Yield As Affected By Phosphorus Placement and Tillage Interaction: A Meta-Analysis.

Phosphorus (P) placement and tillage interactions have been extensively studied for corn and soybean production in the Midwestern states of the US.  The objective of this study was to conduct a meta-analysis of studies completed in the US Midwest to evaluate the effects of P placement and tillage interaction on corn (Zea mays) and soybean (Glycine max) yield.  Peer-reviewed publications from 1980 to the present were included.  Five of the main databases were searched.  Coding criteria were set to include site identification information, background soil test P (STP) and categorized “below 24 mg P kg^-1” and “above 24 mg P kg^-1”, tillage practice categorized as “no-tillage” and “tillage”, fertilizer P rate categorized as “below 20 kg P ha^-1” and “above 20 kg P ha^-1”, placement as “band” and “broadcast”, and statistical information.  Soybean data were also categorized as “residual” when fertilizer was applied before corn in a corn-soybean rotation with no additional fertilizer applied to soybeans or “fertilized” when fertilizer was applied before soybean planting.  Preliminary results show approximately 37 studies for corn and 23 for soybean that met the specified search criteria. Overall yield levels were lower for not-till compared to tillage. Phosphorus placement show no significant effect on yield across fertilizer application rates. Evaluation for lower P application rates suggest a benefit for band application over broadcast, however this was not statistically significant.