Ammmonium and Nitrate Uptake by Corn (<i>Zea mays</i> L.) as Influenced by Nitrogen Concentration and NH+4 /NO‐3 Ratio¹

Abstract

Abstract 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 NH 4 + and NO 3 − 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 μ M ) at each of 5 NH 4 + /NO 3 − ratios (8.40, 2.46, 1.05, 0.49, and 0.17). Solution NH 4 + , NO 3 − , and pH were monitored and variations kept to a minimum. Uptake rates of NH 4 + and NO 3 − were estimated separately from solution analysis. Maximum dry matter accumulated with an N concentration of 67 μ M . Maximum N uptake occurred for the combination of 303 μ M N and a NH 4 + /NO 3 − ratio of 2.46. Shoot/root ratio increased significantly with increased N concentration, but was unaffected by NH 4 + /NO 3 − ratio. Above 67 μM N, the NH 4 + /NO 3 − ratio of absorbed N tended toward 1.0 as compared with the ratio in solution. There was no significant difference between NH 4 + and NO 3 − in their relative rates of absorption. Increasing the concentration of NH 4 + reduced the NO 3 − uptake rate and increasing the NO 3 − concentration reduced the NH 4 + uptake rate. Each mutually influenced the absorption of the complementary nitrogen form to the same degree.