Reproductive and vegetative responses of different accessions of Microlaena stipoides (Labill.) R.Br. to nitrogen applications and supplementary irrigation in southern Australia

Abstract

Native grasses such as Microlaena stipoides (Labill.) R.Br. have the potential to play an important role in pastures, revegetation and as turfgrasses, but their use to date has been limited by seed supply. The purpose of this study was to investigate, (i) the effect of nitrogen fertilisation on M. stipoides seed production, (ii) the effect of irrigation on seed production, and (iii) the variation among accessions in response to these 2 factors. Microlaena stipoides accessions responded to added nitrogen with an increase in shoot growth, total amount of dry matter produced per plant and in reproductive characters at the end of the harvest season. Higher yields were recorded for high (split) nitrogen treatments in comparison to nil (control) or low nitrogen treatments, with added nitrogen extending seed production. Higher soil moisture regimes produced significantly more reproductive culms, more spikelets per culm, and more seeds per plant when compared to low soil moisture treatments. The frequency of irrigation had more effect on seed yield than the amount of water applied. Microlaena stipoides appears to have a 2–step mechanism for regulating the yield of its summer inflorescences namely; the plant initially responds to a high frequency of rainfall or irrigation events by initiating culms. Numbers of culms and florets per culm that reach maturity are dependent on the volume of water applied. Such a mechanism would assist in the adaptation of this grass to a southern Australian climate, which often exhibits an erratic summer rainfall. While there were differences among the accessions for both reproductive and vegetative characters, they gave a uniform response to the different nitrogen treatments. The responses of 3 accessions to different irrigation treatments were somewhat different but with respect to total number of spikelets produced per plant, they all responded in the same way. Different irrigation management schedules may be required for different cultivars for commercial seed production.