The role of plant mass, basal area and density in assessing the herbage mass response to fertility of some native perennial grasses.

Abstract

The effects of nitrogen (N) application and differing past fertilizer history on the ,preen leaf mass per plant, plant basal area, green leaf mass per unit of plant basal area and the plant density of some native perennial grasses were investigated in pot culture and field experiments. Data on each of these components of herbage mass were assessed, either individually or in combination with each other, as methods of evaluating the responsiveness of some native perennial grasses to increased fertility. Different mechanisms of increasing plant green leaf mass with applied N (pot culture) and superphosphate (field) were deter- mined in different species and these affected the relationship between green leaf mass anti basal area. Species such as Aristida ramosa and Bothriochloa macra increased their green leaf mass per unit of plant basal area but not their plant basal area. In the glasshouse the application of N significantly (P<0.05) increased the basal area of Chloris truncata, Eragrostis leptostachya, Dichanthium sericeum, Sporoholus elongatus, Danthonia linkii and Stipa variabilis. However, in the field long-term superphosphate application only significantly increased the basal area of C. truncata and D. linkii plants. In the field the mean densities of A. ramosa, D. sericeum and C. truncata plants growing at the unfertilized site were significantly higher than those at the fertilized site and the density of E. leptostachya plants was significantly higher (P<0.01) at the fertilized site. These data indicated that the use of either mass per plant, mass per unit basal area, plant basal area or plant density alone could bias the apparent responsiveness of some species to fertility. To accurately determine the effect of management on the herbage mass of individual native perennial grasses in the field either mass per plant and plant density data, or mass per unit basal area, basal area and plant density data should be combined.