Core Ideas Instinct nitrification inhibitor either did not affect or reduced grain yield.Instinct did not positively influence early growth plant height or mid‐vegetative canopy normalized difference vegetative index (NDVI).Broadcasting or injecting urea–ammonium nitrate solution (UAN) did not change corn response to Instinct. The use of nitrification inhibitors with fertilizer N application is an attempt to improve corn (Zea mays L.) N use efficiency while reducing environmental and economic concerns associated with N losses. The objective of this study was to evaluate if the encapsulated formulation of nitrapyrin [2‐chloro‐6‐(trichloromethyl) pyridine], Instinct nitrification inhibitor, would influence corn growth and production when applied with spring preplant urea–ammonium nitrate solution (UAN). A 3‐yr field study was conducted in a randomized complete block design with four replications of a factorial combination consisting of UAN at six incremental N rates (0–225 kg N ha−1), broadcast‐incorporated and injected, and with and without 2.56 L ha−1 (0.56 kg a.i. ha−1) Instinct. In 1 of 3 yr, as well as for the means across years, Instinct applied with UAN had a negative effect of reduced early growth plant height and lower mid‐vegetative canopy normalized difference vegetative index (NDVI) compared with UAN without Instinct. Corn grain yield also had a lower across N rate mean yield with Instinct application in 2 of 3 yr and across all 3 yr. The economic optimum N rate (EONR) with Instinct was 32 kg N ha−1 higher than without Instinct, applied either broadcast or injected. Because Instinct did not provide positive effects on corn growth and yield, the study results indicate that Instinct use with spring preplant applied UAN solution would not be an effective nitrification inhibitor to enhance fertilizer N supply or corn production.

Sulfur (S) is an important nutrient for plant growth and crop yield. In the northern U.S. Corn Belt, a decrease in atmospheric S deposition and an increase in grain harvest have increased the frequency of S deficiency in corn (Zea mays L.) and soybean [Glycine max (L.) Merr.]. Nevertheless, S deficiency remains difficult to predict owing to complex interactions between the production of plant-available sulfate-S from soil organic matter (SOM) mineralization and sulfate-S losses to leaching.Our objective was to measure corn and soybean yield response to four S fertilizers (ammonium sulfate, elemental S, gypsum, and polyhalite) in the 1st year following fertilizer application and in the 2nd (residual) year following fertilizer application in Iowa. Across 4 site-years, none of the S fertilizer products increased soybean yield.Across 12 site-years in the 1st year following application, sulfate-S based fertilizers increased corn yield in 4 site-years while elemental S had no effect. Across 6 siteyears in the second residual year following application, elemental S, polyhalite, and gypsum increased corn yield in 1 site-year while ammonium sulfate had no effect. Laboratory incubations confirmed that there was slower production of plant-available S from elemental compared with sulfate-based fertilizers, potentially explaining the lack of elemental S effect in the 1st year following application. In contrast to our expectations, there was a weak, but positive relationship between corn yield response to S fertilizer and SOM concentration. Overall, the kinetics of S fertilizer mineralization and solubility appear to affect the magnitude and timing of crop response to S fertilizer.

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The use of nitrification inhibitors with fertilizer N is an attempt to improve corn (Zea mays L.) N use efficiency while reducing environmental and economic concerns associated with N losses. The objective of this study was to evaluate if the encapsulated formulation of nitrapyrin [2-chloro-6-(trichloromethyl) pyridine], marketed as Instinct nitrification inhibitor, would influence corn growth and production when applied with spring preplant urea-ammonium nitrate (UAN) solution. A three year field study, with a soybean [Glycine max (L.) Merr]-corn rotation, was conducted in a randomized complete block design with four replications of a factorial combination consisting of UAN at six incremental N rates (0 to 225 kg N ha -1 ), broadcast-incorporated and injection applied, and with 2.56 L ha -1 (0.56 kg a.i. ha -1 ) and without Instinct. In one of three years, and for means across years, Instinct applied with UAN had a negative effect, with reduced early growth plant height and lower mid-vegetative canopy normalized difference vegetative index (NDVI) compared to UAN without Instinct. Corn grain yield, in two of three years and across years, also had a lower across N rate mean yield with the Instinct application.

Fall applied liquid swine (Sus scrofa domesticus) manure (LSM) can lead to economic and environmental concerns due to potentially enhanced NO 3 loss. Objectives of this study were to evaluate LSM application timing and use of Instinct nitrification inhibitor, and compare to anhydrous ammonia (AA). Treatments were a no-N control, AA (without Instinct), and LSM with three Instinct rates applied each of 3 yr on October 1 (early fall) and November 1 (late fall). The effect of Instinct was inconsistent. Instinct increased soil NH 4-N concentrations in fall (only early fall LSM application) and spring sampled LSM injection zones. However, in the late spring Instinct had no effect to minimal positive effect on soil inorganic-N, and the high rate was not more effective than the low rate. Corn (Zea mays L.) canopy normalized difference vegetative index (NDVI) was not influenced by Instinct or different between N source, and greatest with late fall N application. Across years, Instinct increased corn grain yield only when early fall applied with the low rate. However, LSM with Instinct had lower yield compared to AA. Waiting to apply N in late fall provided increased inorganic N retention, and with LSM higher corn yield. Based on this study, AA was a better fall applied N source compared to LSM with or without Instinct. A decision to use Instinct with LSM must weigh cost of the inhibitor against other options, such as delayed fall or spring application, or use of AA. 1 INTRODUCTION Iowa leads the USA in swine production with more than 6000 swine operations and over 40 million head marketed annually (NASS, 2019). That production level has resulted in areas within the state where large quantities of nutrients from swine manure are available for use in crop production. Research conducted by Risse et al. (2001) found LSM