Effects of Differences in Phosphorus Nutrition on the Nitrogen Content and Phosphorus 32 Absorption of Four Species of Grass

Abstract

1. Plants of four species of grass, Andropogon ischaemum, the King Ranch bluestem strain; Bouteloua curtipendula, side-oats grama; Eragrostis trichodes, sand lovegrass; and Sorghastrum nutans, Indian grass, were grown from seed in sand culture and provided with available phosphorus over periods varying from 2 to 7 weeks. Sample plants were then fed P32 by the root-absorption method. Subsequently each sample was analyzed for Kjeldahl nitrogen, total phosphorus, and total radiophosphorus. 2. In all four species plants fed phosphorus for only 2 weeks made significantly less growth than those fed for longer periods. Because of the variations involved and the fact that all four species are perennials, no conclusions can be drawn concerning the relationship between later phosphorus absorption and total growth. In general, plants fed phosphorus for periods of from 3 to 7 weeks did not make much greater growth than those fed phosphorus for only 2 weeks. In every case, however, the absorption of phosphorus continued throughout the experimental period. 3. There were distinct differences among the species in the amount of phosphorus accumulated on a dry-weight basis. The amount of P32 absorbed appeared to be conditioned by the amount of phosphorus already in the tissues, those plants containing the greatest amount of phosphorus absorbing the greatest amounts of P32. These plants were also the largest. 4. The inverse relationship reported by others between phosphorus and nitrogen absorption does not find support in the data reported here. This may be a result of the fact that the nitrogen supply was purposely maintained at a fairly high level throughout the experiment.