Fate of Tagged Nitrogen Fertilizer Applied to Irrigated Corn

Abstract

A field experiment was conducted for 2 years with ammonium sulfate tagged with 5.93 atom % 15N to determine the fate of N fertilizer applied to sprinkler‐irrigated corn (Zea mays L.). All areas of triplicate, 356‐cm square plots were treated with 50 or 150 kg tagged N/ha. N fertilizer used by the crop and that remaining in the top 240 cm of soil were measured. NH4+‐N and NO3‐‐N in the 0‐ to 10‐cm layers after the second harvest also were determined. Grain yields in 1976 did not differ significantly. In 1977 response to N was significant, but responses to two N rates did not differ significantly.Only about one‐fourth of the N fertilizer at either rate was removed by the grain. Amounts in the soil were in proportion to amounts applied and about three times more after 2 years than 1 year, reflecting the N in crop residue from the first crop. The N balance indicated losses from the system of 17 to 18% of the N applied during the 2 years, after correcting for apparent errors. Fertilizer did not significantly alter amounts of soil N used by the crop but total N uptake increased with each fertilizer increment. There was no priming effect on mineralization of indigenous soil N. Comparng the 15N and difference methods for calculating fertilizer N uptake showed that the difference method varied more and showed significantly less uptake in one case.From 65 to 73% of the N fertilizer remaining in the soil was in the 0‐ to 10‐cm layer. Depth of movement was related to amount applied, varying from 20 cm with 50 kg after 1 year to 240 cm with 150 kg applied each year for 2 years. Some of the N with the 150‐kg rate may have leached below 240 cm after 2 years, but there appeared to be no leaching from the measured zone in other cases so losses from the system must have been by denitrification.Most of the N fertilizer in the 0‐ to 10 cm‐layer after 2 years was immobilized with only 4.4 to 4.7% remaining in the NH4+ and NO3‐ forms. However, there was about seven times more inorganic N in the soil originating from fertilizer than came from indigenous soil N, which confirms that residual fertilizer N is more likely than indigenous N to be present in inorganic forms.Amounts of fertilizer N found in grain and lost were proportional to amounts applied. The 150 kg N/ha rate gave no higher grain yields than 50 kg N/ha rate, but resulted in much greater crop removal, gaseous loss, and downward movement into the soil profile.

Variability in Optimum Nitrogen Rates for Maize

“…Nitrogen use efficiency for maize in the United States has increased more than 30% over the last 20 yr (Fixen and West, 2002). Early 15 N work with maize showed that 24.1 and 26.4% of the applied N was accounted for in the grain at N rates of 50 and 150 kg N ha -1 , respectively (Olson, 1980). Similar studies by Wienhold et al (1995) reported that maize grain use of N applied averaged 35%.…”

“…Using a fixed NUE for these trials when combining over locations and years would likely compress the variability in optimum N rates reported. Other estimates of NUE exist and are in the 30 to 40% range (Cassman et al, 2002;Olson, 1980;Olson and Swallow, 1984). Also, computing NUE by individual site was not possible because grain N concentrations were only reported in a few of the papers included in this work.…”

Utilisation de l'engrais azoté marqué au 15N par le maïs selon les modes d'application et les doses d'azote

“…Comme la dose 180 dépasse le besoin de la plante en azote, l'engrais azoté est utilisé moins efficacement dans ce cas. Legg et al (1979), Olson (1980), Kitur et al (1984), Liang et MacKenzie (1994a), ont aussi observé que les coefficients d'utilisation de l'engrais azoté tendent à diminuer avec les doses d'engrais.…”

“…Olson (1980) a trouvé après deux ans de culture du maïs des valeurs moyennes de CUR plus élevées pour la dose 50 kg N ha -1 en comparaison à 150 kg N ha -1 . Une diminution significative de CUR a été observée par Liang et MacKenzie (1994a) quand la dose d'azote augmente de 170 à 400 kg ha -1 .…”

Strengths and Limitations of Nitrogen Rate Recommendations for Corn and Opportunities for Improvement

“…These values are based mostly on research with 15 N tagged fertilizer where recoveries of N in corn grain ranges from 13 to 45%, and the amount not recovered in the soilplant system ranges from 23 to 64% (Olson, 1980;Kitur et al, 1984;Sanchez and Blackmer, 1988;Varvel and Peterson, 1990). There is much concern about unrecovered N fertilizer percentages that range from 23 to 64%, which is 40 to 108 kg N ha -1 if a rate of 168 kg N ha -1 is applied, because N that is not recovered in the root zone can lead to water and air pollution.…”