Ammmonium and Nitrate Uptake by Corn (Zea mays L.) as Influenced by Nitrogen Concentration and NH+4 /NO-3 Ratio
1973
Warncke, D. D. | Barber, S. A.
Corn (Zea mays L.) absorbs both ammonium and nitrate forms of N. Both are usually present in the soil and some control of their proportions can be obtained by controlling nitrification. Little is known about the relative rates of absorption of these ions or their effect on plant growth rate when both are present. We investigated the effects of NH₄⁺ and NO₃⁻ on corn by growing 13-day-old corn seedlings for an additional 5 days in 25 nutrient solutions consisting of 5 N concentrations (15.9, 67.1, 303, 1507, and 6015 μM) at each of 5 NH₄⁺/NO₃⁻ ratios (8.40, 2.46, 1.05, 0.49, and 0.17). Solution NH₄⁺, NO₃⁻, and pH were monitored and variations kept to a minimum. Uptake rates of NH₄⁺ and NO₃⁻ were estimated separately from solution analysis. Maximum dry matter accumulated with an N concentration of 67 μM. Maximum N uptake occurred for the combination of 303 μM N and a NH₄⁺/NO₃⁻ ratio of 2.46. Shoot/root ratio increased significantly with increased N concentration, but was unaffected by NH₄⁺/NO₃⁻ ratio. Above 67 μM N, the NH₄⁺/NO₃⁻ ratio of absorbed N tended toward 1.0 as compared with the ratio in solution. There was no significant difference between NH₄⁺ and NO₃⁻ in their relative rates of absorption. Increasing the concentration of NH₄⁺ reduced the NO₃⁻ uptake rate and increasing the NO₃⁻ concentration reduced the NH₄⁺ uptake rate. Each mutually influenced the absorption of the complementary nitrogen form to the same degree.
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