Corn Product Response to Nitrogen Strategy

Trial Overview

• Nitrogen is an expensive input. The cost of nitrogen can vary widely between years causing the cost of this input to fluctuate significantly. In a 2017 trial, corn products responded differently to how nitrogen was applied. Some corn products had similar yields to an all-upfront nitrogen application compared to fertigating nitrogen throughout the growing season, while other corn products yielded more with the fertigation treatment.
• This study was conducted to evaluate if nitrogen application strategy impacted corn products differently in terms of grain yield.

• A standard formula was used to determine nitrogen (N) application rates:

— N need = (yield goal * 1.1) – soil N – legume credit

— 188 lb/acre = (270 * 1.1) – 69 lb soil N in 2 ft – 40 lb/acre

• N treatments were as follows:

— All N upfront – 30 lb/acre of N was strip-tilled prior to planting followed by 160 lb/acre of N applied with 360 Y-DROP® four days after planting (DAP).

— Fertigation – 30 lb/acre of N was strip-tilled prior to planting followed by 40 lb/acre of N applied with 360 Y-DROP® four DAP. An additional five applications of 15 lb/acre of N were applied through the subsurface drip irrigation (SDI) system over the growing season.

• All treatments had a base level 109 lb/acre of N from residual N in the soil and N credit from the previous soybean crop as detailed in Table 1.

• The study was a split-plot with nitrogen strategy as the whole plot with four replications.
• Corn products were grown under full irrigation which was met using the SDI system. Total irrigation applied was 3.4 inches over the growing season. Timely rainfall events occurred from June through mid-August that limited the need for supplemental irrigation.
• Twenty-four corn products were evaluated.
• All weeds were controlled as needed. No fungicide or insecticide were used in crop.

Understanding the Results

• Corn yield was similar between the all-upfront and the fertigation treatments with both treatments yielding 269 bu/acre when averaged across all corn products. However, the fertigation treatment had 45 lb/acre less nitrogen, which caused the fertigated corn products to use less nitrogen to produce a bushel of corn as detailed in Figure 1.

• Corn product yield did not respond differently to nitrogen strategy. This contrasts with the 2017 trial where corn products did respond differently. The inconsistency in the results between years could be attributed to a couple of factors.

— First, 45 lb/acre less nitrogen was applied in the fertigation treatment. This occurred because of some mechanical problems and the timely rainfall in 2018. Because of the rainfall, only 3.4 inches of water were applied, which limited the opportunities for nitrogen to be applied through the SDI system.

— Second, because of the moist soil conditions, the root system likely remained active throughout the growing season instead of going dormant in the top six inches of soil, which allowed for better nutrient extraction.

• Nitrogen efficiency was greatest for the corn products fertigated over the growing season compared to an all-upfront nitrogen strategy. 
• Corn products had similar yields in the all-upfront nitrogen strategy compared to fertigation, which had 45 lb/acre less nitrogen applied. This is important because at $265.00/ton of 32-0-0 it represents a 6.5 cents/bushel or $18.63/acre savings in nitrogen cost.