Influence of ammonium: Nitrate ratios on the growth and nitrogen uptake of pearl millet

Abstract

Pearl millet [Pennisetum glaucum (L.) R. Br.] is a potentially high‐yielding grain crop for the Southern Coastal Plain region of the USA. Information on the growth and N nutrition of pearl millet is limited; therefore, this study was initiated with the objective of studying pearl millet growth, N content, N uptake patterns and N‐form preference. Plants were grown in solution culture using a modified Hoagland's solution. Solutions were changed weekly and transpirational losses replaced daily. The N‐form ratios were 1:0, 3:1, 1:1, 1:3 and 0:1 NH₄ ⁺ to NO₃ ^‐ Uptake was determined by difference between the initial and final solutions. Nitrate and NH₄ ⁺ uptake patterns were different from each other and were influenced by the ratio of NH₄ ⁺ to NO₃ ^‐. After the plants had been transferred to the solutions, ammonium was preferred for the first two weeks, with NO₃ ^‐ preferred thereafter. Nitrate uptake was highest during the grain filling period. Plant growth as measured by leaf, stem, root, and seed weight, plant height, average seed weight, and head length was generally reduced as NH₄ ⁺ increased. The largest reduction was observed between the 3:1 and 1:0 ratios. Ammonium nutrition had an overall negative effect on pearl millet growth. Ammonium fertilization of pearl millet under conditions that increase absorption of NH₄ ⁺ over NO₃ ^‐ may have a negative effect on pearl millet growth and development.