Summer-growing perennial grasses are a potential new feed source in the low rainfall environment of southern Australia

Abstract

In the Mallee region of southern Australia, the dry and variable climate results in frequent summer–autumn feed gaps, restricting the profitability of farms that combine livestock and crop enterprises. To assess the suitability of summer-growing perennial grasses to fill such feed gaps, two replicated field experiments comparing the persistence and productivity of several cultivars were conducted at Hopetoun and Karoonda. The data from these experiments also served to validate a C4 grass model, which was then used in a simulation experiment comparing productivity on two different soil types at three locations. Most grass cultivars established well except on sandy, non-wetting soils. At Hopetoun, four of five cultivars persisted over 6 years, demonstrating the tolerance of the selected cultivars to the typical long, dry summers and cold, wet winters of the region. Biomass production showed little difference between cultivars and a strong response to the amount of summer rainfall, ranging from 1500 to 3000 kg ha–1 under average seasonal conditions and peaking at 9000 kg ha–1 in the very wet summer of 2010–2011. Model performance was satisfactory (R2 0.85–0.93, RMSE 476–1673 kg ha–1, depending on the cultivar), in terms of predicting both the magnitude and the timing of biomass production. Simulation outputs indicated that biomass production closely followed seasonal trends in temperature and moisture availability. Grazing potential was highest from early summer to autumn, which coincides with the period of feed shortages and highest marginal value of forage. In areas with warm-season (October–April) rainfall averages of 175 and 225 mm, the grazing of C4 grass pastures on marginal soils would be possible in at least 40% of the years for 2 and 3 months, respectively. It was concluded that summer-growing perennials are a promising option to alleviate feed gaps on mixed crop–livestock farms in areas with at least 150 mm of rainfall from October to April.

Nitrogen cycling in summer active perennial grass systems in South Australia: non-symbiotic nitrogen fixation

“…The site has a Mediterranean climate with an annual rainfall of 250-350 mm and a warm season rainfall of 133 mm. Full details of experimental setup and biomass development are reported by Descheemaeker et al (2014). The grass cultivars studied were: Megathyrsus maximus Jacq.…”

“…Premier (Premier digit grass). Average plant numbers per m 2 for the Rhodes grass were generally higher (22-36 plants m 2 ) than for other grass species (1-8 plants m 2 ) (Descheemaeker et al 2014). Dry-matter cuts of plant material from a minimum of two areas of 1 m 2 were collected during February and April, dried and recorded for aboveground plant biomass measurement.…”

“…2) (Descheemaeker et al 2014). The total plant biomass estimates observed in April for Rhodes grass are similar to that reported in the Western Australian wheatbelt .…”

“…Farming systems that rely on annual pastures and crops are considered less effective than deep-rooted perennials for drying the soil profile, minimising deep drainage and managing dryland salinity (Angus et al 2001;Dear and Ewing 2008). Summer-active perennials not only have the ability to use excess water, they also contribute to feed and play an important role in grazing systems (Descheemaeker et al 2014). Some perennial species could be grown with crops in alley cropping (also known as pasture cropping), or in long-term pasture phases or in phased rotations with crops.…”

“…Despite there being strong evidence for rhizosphere-associated N 2 fixation with perennial grasses from overseas (Chowdhury et al 2009), there is no direct evidence on this topic in Australian environments. A replicated field experiment was established at Karoonda, South Australia, to test whether summer-active perennial grasses can be included as a feed-gap measure in cropping systems (Descheemaeker et al 2014). In the present study, our objective was to quantify N inputs by NS N 2 -fixing bacteria associated with summer-active perennial grasses during summer.…”