Corn growth and yield response to starter fertilizer
In previous research in continuous corn with no-till management, starter fertilizer consistently increased vegetative plant development rate and plant dry matter prior to sidedressing and decreased grain moisture. However, increased yield did not always occur. The objective of my study was to evaluate the effects of starter fertilizer on plant dry matter and nutrient content throughout the growing season to determine if differences in these parameters determined early in the growing season persisted throughout reproductive growth and explained yield effects. Experiments were conducted in long-term continuous corn no-tillage fields at SEPAC, NEPAC, and TPAC in 2019 and 2020. At TPAC, treatments were control and starter, 46 kg N ha-1 and 18 kg P ha-1. At SEPAC and NEPAC, we also evaluated starter fertilizer composition, and the treatments were control, 3.6 kg N ha-1 and 8 kg S ha-1; N, 34 kg N ha-1 and 8 kg S ha-1; NP, N plus 7.5 kg P ha-1; and NPK, NP plus 9.5 kg K ha-1. Starter fertilizer was applied 5 cm below and 5 cm to one side of the seed. Total N rate was equalized by adjusting the N application at sidedressing to compensate for the N applied in starter.
Although starter fertilizer treatment effects differed from those of the control, in most cases starter fertilizer effects were the same regardless of composition. Hereafter, ‘starter fertilizer’ will refer to the mean of the three starter fertilizer treatments, N, NP, and NPK for SEPAC and NEPAC or NP in the case of TPAC. Crop growth rate determined by the number of collared leaves was increased by starter fertilizer, compared to the control, at all site-years. Starter fertilizer increased leaf appearance up to one leaf in plots evaluated at the same point in time and final leaf number was also one more leaf per plant. Starter fertilizer increased dry matter as early as V4 compared to the control at SEPAC and TPAC, with differences maximizing around V6-V12. Effects at NEPAC were inconsistent throughout the season. At reproductive stages the magnitude of the differences in dry matter decreased until starter fertilizer and control treatments had similar dry matter at maturity. Before sidedressing, N and P concentrations were greater with starter fertilizer than the control, but after sidedressing concentration of these nutrients were greater with control than starter fertilizer. The differences in N and P concentration between starter treatments and the control increased in later vegetative stages, but decreased during reproductive stages and at maturity. Potassium concentration was generally unaffected by the fertilizer treatments. Plant nutrient content differences between starter fertilizer treatments and the control were similar to differences seen with dry matter, despite the differences in nutrient concentration between starter fertilizer and the control. When compared at the same growth stage, starter fertilizer treatments and the control, had similar DM and nutrient concentration and content. Starter fertilizer, compared to the control, resulted in earlier silking and/or tasseling at all site-years. Starter fertilizer accelerated vegetative crop development, but this did not result in substantial differences in dry matter or nutrient content at similar growth stages, including physiological maturity. Despite this result, increased grain yield with starter fertilizer, compared to the control, occurred at 3 of 6 site-years and ranged from 300 to 1000 kg ha‑1. Grain moisture was decreased by starter fertilizer at 4 of 6 site-years by at least 5 g kg-1.