Soil Fertility Management for High Population Corn Production.

The objectives of this research are to determine the optimum N timing and rate, and critical Mehlich-3 soil test P and K for high population, narrow row corn production systems. A series of 15 N fertilizer response experiments were conducted on Tidewater, Coastal Plain, Piedmont, and Mountain (grain and silage) region sites during 2010 to 2012. An additional series of P and K response tests were conducted on Tidewater, Coastal Plain, and Piedmont region long-term soil fertility test plots. When all N response tests were pooled, analysis of variance found the main effect of N was significant for yield & all 3 ear yield components.  There were few significant interaction effects with N, indicating that this effect was relatively consistent regardless of possible differences among sites, row spacing, or application timings.  There was no evidence of significant mortality (plant stand) or barren stalk (ear density) effects due to N rate, but ear yield components and grain yield increased as N rate increased, at least up to the 166 lb N/ac rate. The interaction effect of timing and “environment” was significant, i.e. any effect of timing was not consistent among all of the experimental site-years.  In all 3 individual site-years where the timing effect was significant, yield for sidedress > yield for all N applied at planting (p<0.05). Environment (site-year)  x row width interaction effects were also significant, and in all cases where differences were noted, mean yields were higher with narrow row than with wide row.  Corn yield component (# rows per ear, # kernels per row, and kernel size) responses, and responses to soil P and K fertility levels will also be discussed.