Response of grasses to nitrogen source.
Abstract
Yield responses of various grasses to ammonium-N and nitrate-N were investigated in pot trials. Yields with nitrate-N as a percentage of those with ammonium-N were, for ruderal species: Eragrostis racemosa 94, Setaria palludifusca 84, Pennisetum setaceum 83 (differences not significant); for pioneer species: Pogonarthria squarrosa 76, Sporobolus pyramidalis 76, Aristida adscensionis 52 (differences highly significant); for climax species: Heteropogon contortus 48, Schizachyrium jeffreysii 42, Andropogon schirensis 39, A. gayanus 30, Hyparrhenia filipendula 30, Danthoniopsis intermedia 22. Yields of climax species were much lower than those of pioneer or ruderal species. Total cation concentrations were not consistently affected by source of N. All species were high in Al, and perennials were high in Mn. Most Al and Fe was retained in the roots, whereas Mn was more evenly distributed in the plant. Cation composition of all species resembled that of calcifuges. In further pot trials, adding Ca increased yields of Cenchrus ciliaris and decreased yields of Aristida rhiniochloa and H. contortus when fertilized with ammonium-N but not nitrate-N; 8 other species were unaffected. It was suggested that succession in high-altitude African grassveld was towards the calcifuge habit.