Nitrogen‐15 Evaluation of Fall‐Applied Anhydrous Ammonia: I. Efficiency of Nitrogen Uptake by Corn

Abstract

Fall application of anhydrous ammonia (NH3) is a common practice for corn (Zea mays L.) production in the midwestern United States, but evaluations to date have relied entirely on yield comparisons that provide no means of distinguishing fertilizer from soil N uptake. To quantify fertilizer N uptake efficiency (FNUE) when using this practice, field trials using 15NH3 were conducted between 2016 and 2018 at four sites in a corn–soybean (Glycine max L. Merr.) rotation and at two sites under continuous corn. At each site, 224 kg N ha−1 was applied with and without the use of nitrapyrin (NP) to inhibit nitrification. Relative to grain yields without fertilizer N, response to fall N fertilization occurred at four of the six sites studied, averaging 53% (4.0 Mg ha−1) in two growing seasons with below‐normal rainfall. The use of NP was beneficial at only one site for increasing total N uptake, but resulted in a decrease at another, along with a significant reduction in grain yield. Isotopic estimates of FNUE (i.e., F15NUE) ranged from 12 to 34% (21% on average) for grain and from 16 to 42% (28% on average) for total aboveground biomass, and N derived from fertilizer ranged from 20 to 46% (32% on average). Both isotopic parameters were highest for the site lowest in native N availability, demonstrating the potential of site‐specific N management to improve fall NH3 fertilization by accounting for soil N mineralization.

Nitrogen‐15 evaluation of fertilizer placement at planting for corn production

“…Comparison of Tables 8 and 9 shows that F 15 NUE was generally lower in 2021 than in 2017, which reflects greater rainfall (Table 3) that would have promoted mineralization, the result being an increase in dilution of fertilizer N by soil‐derived N. The same effect explains why F 15 NUE was lower with a higher level of organic C at Sites 1, 3, and 5 than for Sites 2 and 4. Both findings are consistent with what has been reported in previous 15 N field studies involving contrasting sites and/or weather conditions (e.g., Chalk & Keeney, 1975; Griesheim et al., 2019; Ma et al., 2004; Meisinger et al., 1985; Schindler & Knighton, 1999; Tran et al., 1997).…”

“…For both growing seasons studied, dry matter production without fertilization was consistent with what was observed for overlapping site‐years in other 15 N studies aimed at evaluating fall applications of anhydrous NH 3 (Griesheim et al., 2019) or in‐season placement of UAN (Griesheim et al., 2022). Consistencies were also observed when comparing grain yields from fertilized plots with county‐level data, which averaged slightly lower in 2017 (11.3 Mg ha −1 ) than in 2021 (11.5 Mg ha −1 ) when expressed on a dry‐weight basis (https://www.nass.usda.gov).…”

“…Linear mixed models were constructed and a two-way ANOVA with a type 3 test of fixed effects was performed, and the Tukey method was utilized to separate treatment means at p < 0.05. As previously done for overlapping site-years in other 15 N studies (Griesheim et al, 2019(Griesheim et al, , 2022, data were analyzed in R (R Core Team, 2014) using lme4 (Bates et al, 2015) with treatments and sites as fixed effects and replications as a random effect.…”

Isotopic evaluation of in‐season Y Drop applications for corn production

“…To ensure a true dry weight, all plant samples were further dried for at least 12 h in a forced‐air oven (50 °C) before total N analysis by semimicro Kjeldahl digestion (Bremner, 1996) and diffusion (University of Illinois, 2022). The digestion technique used a KMnO 4 –reduced Fe pretreatment, modified as described previously (Griesheim et al., 2019) to reduce frothing, and a block digester (Seal Analytical Model BD50) programmed to carry out heating in four steps subsequent to a 20‐min treatment with 0.3 M KMnO 4 (1 ml) and 9 M H 2 SO 4 (2 ml). In this program, the sample was heated at (a) 90 °C for 45 min after addition of Fe powder (0.5 g); (b) 150 °C for 2 h following addition of K 2 SO 4 –catalyst mixture (1.1 g) and 18 M H 2 SO 4 (3 ml); (c) 250 °C for 2 h; and (d) 350 °C for 5 h. Ammonium‐N in the digest was liberated by alkaline diffusion, quantified titrimetrically, and processed for N‐isotope analyses with an automated Rittenberg system (Mulvaney et al., 1990).…”

“…The implication is greater mineralization, which not only reduces crop N response but also enhances mineralization-immobilization turnover that would amplify discrepancies between the two estimates of FNUE (Schindler & Knighton, 1999). The trials in 2017 were carried out at the same sites as a study evaluating fall-applied 15 NH 3 with and without nitrapyrin, for which F 15 NUE values reported by Griesheim et al (2019) ranged from 18 to 24% in the grain and from 28 to 32% in the total aboveground biomass. Higher efficiencies were expected with UAN applied at planting or by sidedressing but are not apparent from Table 10, based on F 15 NUE values that ranged from 12 to 30% for grain and from 14 to 37% for total aboveground biomass.…”