Fate of Tagged Nitrogen Fertilizer Applied to Irrigated Corn1
- R. V. Olson2
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.Please view the pdf by using the Full Text (PDF) link under 'View' to the left.
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