The effects of starter fertilizer on root and shoot growth of corn hybrids and seeding rates and plant-to-plant variability in growth and grain yiel

Starter fertilizer often increases early-season growth of corn; however, yield responses have varied. Yield responses often occur on soils with low soil fertility, however, have occurred on soils with high fertility. Currently, farmers are attempting to reduce plant-to-plant variability in growth and development to maximize grain yield. Farmers have asked if placing starter fertilizer near the seed could reduce plant-to-plant variability with the hypothesis that uniform fertility will result in uniform plants. We conducted two experiments near Ames, Iowa, and Nashua, Iowa with similar treatments and data collection. Starter fertilizer was banded 5 cm below the seed and 5 cm to the side of the seed consisting of fertilizers containing nitrogen and phosphorus (monoammonium phosphate and ammonium polyphosphate). Three hybrids were planted at three seeding rates with and without starter fertilizer. Treatments were arranged in a complete factorial randomized complete block design. We measured ten tagged plants per plot for height, stem diameter, and developmental stage multiple times through the season. We also collected anthesis and silking dates on these plants, and hand harvested and measured grain yield components after maturity. Plant height and stem diameter were measured on five untagged destructively sampled plants at the same time as the plants taken to hand harvest. We developed equations to correlate plant height and stem diameter to plant biomass to estimate plant biomass on tagged plants. We used the coefficient of variation to describe variability in plant growth and grain yield per plot. Starter fertilizer increased early season growth and the developmental rate of corn. Starter fertilizer increased plant-to-plant variability in growth at the low seeding rate in Ames one year. Grain yield increased with starter fertilizer in 2012; however, the response was related to low fertility.