Response of Continuous Corn to Varying Rates and Placements of Starter Fertilize

Previous research has shown that starter fertilizer, a small amount of fertilizer placed with or near the seed at planting, often accelerates early season growth and increases biomass production, but does not always increase grain yield in corn (Zea mays L.). Our objective was to evaluate the effects of starter fertilizer on crop growth and development, as well as grain yield and moisture in continuous corn cropping systems. Treatments consisted of no fertilizer applied at planting (Control), a "Popup" application of 3.8 kg N ha-1 and 5.8 kg P ha-1 placed in-furrow with the seed (PU), an application of 19.8 (DPAC) or 28.1 kg N ha-1 (PPAC, NEPAC, and SEPAC) and 11.0 (PPAC), 5.8 (NEPAC), 7.7 (DPAC) or 6.1 (SEPAC) kg P ha-1 placed 5 cm to one side and 5 cm below (5x5) the seed (S), a combination of 3.8 kg N ha-1 and 5.8 kg P ha-1 applied in-furrow with 17.1 (DPAC) or 24.3 kg N ha -1 (PPAC, NEPAC, and SEPAC) and 9.4 (PPAC), 5.0 (NEPAC), 6.7 (DPAC) or 5.3 (SEPAC) kg P ha-1 applied 5x5 (P+S), and an application of 39.8 (DPAC) or 56.2 kg N ha-1 (PPAC, NEPAC, and SEPAC) and 21.9 (PPAC), 6.1 (NEPAC), 15.6 (DPAC) or 12.3 (SEPAC) kg P ha-1 placed 5x5 cm (SH). At the NEPAC location, 2.8 kg S ha-1 was applied across all treatments in the 5x5 cm position. The total N rate applied, but not P rate, was equalized across all treatments with variable sidedress N rates. The study was conducted in 2014 and 2015 at three locations, and in 2016 at four locations with varying weather conditions, soil types, and management practices.;Final plant population was generally unaffected by starter treatments. Crop growth and development responses to starter fertilizer treatments were similar across all locations. Starter fertilizer accelerated the rate of leaf collar appearance throughout the vegetative growth period, beginning as early as the one to two leaf collar stage (V1-V2). As the season progressed, phenological differences among the treatments increased even after total applied N was equalized with the sidedress N applications. Flowering and physiological maturity occurred sooner in the P+S and SH treatments than in the Control or PU treatments while in the S treatment, the timing of flowering was intermediate. In addition to increasing leaf collar appearance, starter fertilizer treatments that received at least 28 kg N ha-1 and 6 kg P ha-1 also increased the total number of leaves plant-1 produced at all four locations it was measured compared to the control. Ear leaf number was also increased by the addition of at least 28 kg ha-1 of N and between 6 and 15 kg P ha -1 at planting, but to a lesser extent than the total leaf number.;Dry matter increased 95% when plants received the SH treatment relative to the control while all other treatments had intermediate effects. In 2015, whole plants were sampled at the V6-V7 growth stage and whole plant nutrient concentrations generally decreased as the amount of N and P applied as starter fertilizer increased. In 2016, sampling was done earlier at the V4-V5 growth stage and the opposite was observed for N concentrations, but all other nutrients responded similar to 2015. Whole plant nutrient content was generally increased with starter fertilizer and was largely driven by dry matter accumulation differences. There were few instances in which ear leaf nutrient concentrations differed. At the locations in which they did, the trend was similar to the results from the whole plant sampling in that concentrations decreased as the amount of applied N and P increased at planting. Grain nutrient concentrations were the least effected by starter fertilizer and at locations in which a response occurred, results were variable.;The number of kernel rows ear-1 (KRE) was influenced by starter fertilizer at one of four locations where it was measured and was decreased by the two treatments in which the 5x5 cm placement was used. The total number of kernels ear-1 (TKE) was increased by starter fertilizer at two of four locations and at one location was decreased by the PU treatment. The two locations that did see an increase of TKE from starter fertilizer had a significant grain yield response at harvest. Kernel weights (KW) were decreased by adding at least 28 kg ha-1 and 6 kg P ha -1 of N at planting at one location, and were increased by the P+S treatment at another. No differences were observed at the remaining two locations. Both locations in which differing KW were observed also saw increased TKE. On average, grain moisture of the PU, S, P+S, and SH treatments were 6, 11, 14, and 17 g kg-1 lower than the control treatment. However, grain yield was increased by starter treatments at only 4 of the 10 locations. The PU treatment only increased yield at 1 of the 10 locations, increasing yield by 370 kg ha-1. Yield was increased by 497, 587, and 775 kg ha-1 on average when plants received the S, P+S, and SH treatments respectively compared to the control at the four responsive locations.