Corn Response to Incremental Zone-Placed Nutrients

• Place nutrients close to the crop row to minimize risk of loss and increase nutrient availability.
• Focus a fertility program on key nutrients that may be limiting for given yield goals and soil fertility levels.

Crop nutrition is the foundation to achieving maximum genetic yield potential. The Golden Harvest Agronomy in Action research team conducted trials evaluating intensive fertility management practices utilizing precision fertilizer placement and timing. The trial was designed to better answer 3 main questions:

1. Can zone-applying incremental amounts of macronutrients — nitrogen (N), phosphorus (P), potassium (K) and sulfur (S) and zinc (Zn) — in addition to the grower base-applied fertility rates increase yield potential?
2. Does increasing the rate of N within the incremental nutrients applied at planting further enhance yield potential?
3. At locations responsive to additional N, does delaying the application to the V6 timing influence the response?

To better understand these questions, 3 incremental zone-placed fertility treatments were compared to the grower-defined base fertility program at 9 Midwest locations in 2022. Nutrients, rates and placement of the 3 treatments are outlined in Table 1.

Precision fertilizer placement was completed using a research planter that can apply seed-safe fertilizer in-furrow on the seed, higher rates of fertilizer in a 2x2x2 placement in addition to dribbling S and/or N next to the row on the soil surface behind the planter (Figure 1). In-season sidedress N applications were made placing N directly beside the row on the soil surface at the V6 crop stage (Figure 2).

Locations varied in soil fertility levels and the base rate of N applied based on local grower management choice (Table 2). All locations had adequate P and K soil test levels except Jefferson, WI, and Malta, IL. Soil P test levels were also below optimum at the Waterloo, NE, site, although K level was adequate.

All locations received between 140-200 lbs. of N/acre as the base rate except for the 2 trials at Blue Earth, MN, where the host farmer was only able to apply 30 lbs./acre of N with their preemergence herbicide program (Table 2). Due to this, both Blue Earth locations were N deficient.

Yield Results

At Blue Earth second location, incremental zone-placed fertilizer increased yields by 11 bu/acre (Graph 1). Since N was a limiting factor, much of the response was likely from the 17 lbs of N/acre rather than the other nutrients applied. Not surprisingly, at the Blue Earth locations, there was a 52-68 bu/acre response when the additional nitrogen (60 lbs/acre) was applied with the planter. Interestingly, although the grower had applied 30 lbs of N/acre and a corn plant takes up less than 20 lbs of N/acre by V3¹, there was still visible growth enhancements from supplemental planter-applied N at that stage (Figure 3). This is an indication that corn plants set their growth trajectory early in the season and it is important to not short crop nutrition during early vegetative growth. Although there were no differences between supplemental N (60 lbs N/acre) application timings at the second Blue Earth location, the planter-applied timing yielded 18 bu/acre more than the V6 timing at the first Blue Earth location (Graph 1).

Jefferson, WI, received a more typical preplant N rate (140 lbs/acre) but experienced multiple heavy spring rain events that resulted in N loss and deficiency symptoms. Incremental zone-placed fertilizer increased yields by 14 bu/acre (Graph 1). The yield response was likely driven by the additional 17 lbs of N/acre from the fertilizer. However, there was likely response to the P²O⁵ and K²O as well, with soil test levels considered below adequate for both nutrients. Plants at Jefferson that received additional N applied with the planter were significantly taller and more robust during vegetative growth (Figure 4) and yields were increased by 32 bu/acre (Graph 1). Nitrogen applied at sidedress yielded 13 bu/acre greater than if applied with the planter, indicating there was N loss with the early N application from heavy rain after planting (Graph 1). Both Sac City, IA, and Waterloo, NE, only saw a response with the early N application yielding 8 bu/acre greater than the base program. Additional N applied with the planter increased yield by 9 bu/acre at Malta, while sidedress N increased yield by 7 bu/acre. Incremental zone-placed fertilizer increased yields by 5 bu/acre and the extra N applied at V6 increased yields an additional 5 bu/acre at Slater, IA (Graph 1).

Summary

Overall, there was smaller responses to incremental zone-placed fertilizer (minus extra N) at most locations and it was difficult to determine which nutrient was responsible for the response. Locations that did have a significant yield increase from zone-placed nutrients without extra N were typically deficient in N. Therefore, the response was likely a result of the small amount of N (17 lbs/acre) included in the fertilizer. Yield increases from the additional 60 lbs of N/acre applied either with the planter or sidedress varied depending on location and the timing of crop N demand.

Due to trial design, we are not able to determine if the incremental P, K, S and Zn had any influence on the size of the nitrogen response. It is possible that although there was a lack of response to these nutrients at many of the locations, the overall nitrogen response may not have been as great without the supplemental P, K, S and Zn. Phosphorus movement in the soil is minimal and must be close to the root system for uptake through diffusion. Young plants with small roots can struggle to uptake P, especially in conditions that slow plant growth, such as cooler temperatures and dry soils. Zone-placed fertilizer may have increased P uptake and root system development ultimately enhancing the yield response to N. Recently, Purdue University did extensive research evaluating in-furrow and 2x2 starter fertilizer in corn from 2014-2021. They found similar results to our study attributing yield increases primarily to the additional nitrogen rather than other nutrients in the starter.²

It is important to understand soil fertility and nutrient uptake patterns in corn. Adding more nutrients does not always mean yields will be enhanced, as demonstrated at both Clinton, IL and Waterloo, NE locations. Crop fertility management should be focused on nutrients that are the limiting factor given yield goals and soil fertility levels.