H.J. "Rick" Mascagni Jr. and Dennis Burns
Many soil types are present in the Mississippi River Delta of Louisiana. Optimal nitrogen application rates and timing are needed for each specific soil type to enhance fertilizer efficiency, increase corn profitability, minimize environmental pollution and to create a database for precision farming practices. Research in other regions of the United States has indicated that fertilizer efficiency is enhanced with sidedress compared to at-planting applications. When nitrogen is sidedressed, an early-season nitrogen deficiency might be avoided by applying a starter fertilizer to supply nitrogen for early growth. The objectives of this study were to determine if time of nitrogen application affected fertilizer efficiency and to determine if an in-furrow starter fertilizer was beneficial with either timing of fertilizer application.
Field experiments evaluating six nitrogen fertilizer rates, two nitrogen application times and two starter fertilizer treatments were conducted from 1996 through 1998 on a Commerce silt loam at the Northeast Research Station near St. Joseph. Nitrogen fertilizer rates ranging from zero to 250 pounds of nitrogen per acre were knifed in on the side of the row (about 10 inches from the drill) at planting or at the six-leaf growth stage (sidedress). Two starter treatments were evaluated, a control and 10 pounds of nitrogen per acre applied infurrow. The fertilizer nitrogen source for all fertilizer treatments was urea-ammonium nitrate solution containing 32 percent nitrogen. Pioneer brand 3167 was planted each year at about 28,000 seeds per acre. The test was not irrigated, and the previous crop was cotton.
Maximum yield occurred at similar nitrogen rates, 150 to 200 pounds of nitrogen per acre, regardless of the time of fertilizer application, at-planting vs. sidedress, in two of the three years. Yields were highest for the at-planting application in 1998, probably because a relatively dry period after the sidedress application may have reduced availability of the fertilizer nitrogen to plants. Similarly, the yield responses to starter fertilizer tended to occur primarily at the lower nitrogen rates (100 pounds of nitrogen per acre and less) and had little effect on optimal nitrogen rates.
Results of this study suggest there is little benefit from sidedressing or using a starter nitrogen fertilizer in lowering optimal nitrogen rates on this Commerce silt loam soil. Growers typically wait until emergence to apply nitrogen fertilizer so they can evaluate plant population and yield potential. If nitrogen is applied sidedress, an application earlier than the six-leaf growth stage (about 30 days after emergence) will better ensure adequate fertilizer activation (availability to plants) by the time the nitrogen requirement of the plant exceeds the native soil supply. The starter fertilizer used in this test contained only nitrogen. Previous Louisiana research has indicated a significant early growth response and, in most years, a yield increase from in-furrow application of starter fertilizers that contain both nitrogen and phosphorus, particularly on the more coarse-textured, sandy soils.
(This article was published in the winter 2000 issue of Louisiana Agriculture.)