Studies on the nitrate nutrition of two indigenous Rhodesian grasses.
The mean nitrate reductase activity (NRA) of leaf tissue, from various nitrogen environments, was four times greater in Sporobolus pyramidalis than in Hyparrhenia filipendula. THe maximum NRA induced in Sporobolus pyramidalis was four times greater than in Hyparrhenia filipendula although leaf nitrate contents were similar. Measurements of the leaf nitrate content of whole plants indicate that nitrate uptake is greater in Sporobolus pyramidalis. In veld situations the NRA of both species decreased in plants growing in sites of a higher successional stage. It is concluded that the seral species, S. pyramidalis, has a greater potential for utilization and absorption of nitrate than the climax species, Hyparrhenia filipendula, though leachable soil nitrate levels did not differ significantly with successional stage. Soil nitrate increased from October to early January then decreased rapidly. The decline appearing to be unrelated to soil moisture and coinciding with an increase in vegetation activity and, therefore, possibly due to nitrification inhibitors.