University of Delaware nitrogen (N) recommendations are based on a realistic yield goal with a base rate of 1 lb N per bushel of expected yield. Increased N use efficiency has been observed when 15 to 25% of the total N is applied as starter fertilizer and the remainder of the N is applied when corn plants are 12 to 15 inches tall (around V5 to V6). This is especially important for corn planted in Delaware’s sandy, low organic matter soils, as these soils are susceptible to N leaching. Ultimately, split applying N to corn will help you get more N in your crop over the growing season.
It is important to consider salt index, placement, and crop sulfur (S) needs when making decisions about starter fertilizer application. Fertilizers are soluble salts that can damage germinating seeds. When N is placed in 2 × 2 placement (i.e., 2 inches beside and 2 inches below the seed), we recommend you apply < 75 lb/acre of N. If you also plan to apply potassium (K) as a starter fertilizer, limit the N + K2O application to 75 lb/acre. Application at higher rates can damage the crop. The closer the fertilizer is placed to the seed, the larger the potential for salt damage. Therefore, we recommend limiting pop-up (in-furrow) N + K2O applications to 10 lb/acre.
Commonly used N containing liquid starter fertilizer products include UAN (30 or 32%) and ammonium polyphosphate (10-34-0 or 11-37-0). These fertilizers may produce ammonia gas as a byproduct, which is also toxic to germinating seeds. Another popular starter fertilizer is ammonium sulfate (8-0-0-9S), which provides readily available S compared to ammonium thiosulfate. High yielding, irrigated corn may require 30 to 40 lb/acre of sulfur, which can be split applied at planting and again at sidedress. Ammonium sulfate also has a strong acidifying effect, which can make certain micronutrients more available in high pH fields, averting deficiencies.
Applying 15-20% of the total N as a starter can sustain your corn until V5 to V6, at which time you can apply the remainder of the N. The sidedress N application occurs around the period of rapid N uptake on the crop.