Effects of depth and time of sowing and over-wintering on tropical perennial grass seedling emergence in northern New South Wales

Abstract

Two studies were conducted in northern NSW to examine some of the factors affecting the successful emergence of seedlings of five species of tropical perennial grasses [Panicum coloratum var. makarikariense cv. Bambatsi (panic), Digitaria eriantha ssp. eriantha cv. Premier (digit), Chloris gayana cv. Katambora (Rhodes grass), Dichanthium aristatum cv. Floren (bluegrass), and Bothriochloa bladhii ssp. glabra cv. Swann (forest bluegrass)]. The first experiment investigated the effects of depth and time (month) of sowing on tropical perennial grass seedling emergence, while a second series of studies examined the effects of contact of dispersal/sowing units with the soil, particularly over winter, on subsequent seed germination and seedling emergence. No seedling emergence of any species occurred in September 2006 and June–August 2007. From October 2006 to May 2007 there were significant effects (P < 0.001) of species, sowing time, depth, and their interaction on predicted emergence. From December to March, predicted emergence was always lower for surface-sown caryopses compared with those sown at 10 and 25 mm depth, and Bambatsi was the only species that had >50% emergence from a depth of 50 mm. Recovery of intact caryopses from 300 μm nylon mesh bags stored in the soil for 6 and 12 months was low for all species. Similarly, predicted germination of caryopses from field soil surface and buried locations (2007 and 2008) and those from florets and coated seeds (2008) was low, indicating that these species had a poor ability to over-winter in moist soil.