Growth rate and nutritive value of sown tropical perennial grasses in a variable summer‐dominant rainfall environment, Australia

Abstract

Growth rate, proportion of leaf and stem and nutritive value of sown tropical perennial grasses have not previously been documented for the dryland, frost‐prone summer‐dominant rainfall region of eastern Australia. An experiment was conducted in northern inland New South Wales with Chloris gayana (Rhodes grass) cv. Katambora and Digitaria eriantha (digit grass) cv. Premier, and compared to Sorghum bicolor ssp. bicolor x S. bicolor ssp. drummondii (forage sorghum). The grasses were harvested every 2 or 6 weeks and fertilized at five rates of nitrogen (N; 0–300 kg N ha−1) over two growing seasons (September–May), 2006–2007 and 2007–2008. Growing season rainfall was below median for both years of the experiment and growth rate was highly variable, reflecting variable rainfall. Sorghum generally had the highest growth rate. Digit grass generally had higher growth rates than Rhodes grass, was more responsive to growing season rainfall, commenced growth earlier and had a longer growing season. Nitrogen application extended the growing season of both perennial grasses. Growth response to N application was minimal when rainfall was low and response following significant rainfall was higher for fertilized than unfertilized grasses. In general, the proportion of green leaf was greater than green stem, although the proportion of stem increased when defoliation interval increased. Nutritive value of the perennial grasses was higher in leaf than stem and declined during the growing season. Differences between the grasses were slight, but indicated that fertilized digit grass defoliated at 2‐week intervals had higher growth rate and nutritive value than Rhodes grass.

Soil water dynamics, herbage production and water use efficiency of three tropical grasses: Implications for use in a variable summer‐dominant rainfall environment, Australia

“…Despite variable rainfall during the experiment, the traditional forage base components, with high yield and WUE, demonstrated why they form the cornerstone of productive livestock systems in this environment (Lodge et al., ). Indeed, it is the highly variable nature of the summer‐dominant rainfall distribution of this environment (Lodge, Brennan et al., ), with frequent agricultural droughts (Lodge & Johnson, ) that requires pastures to be responsive to rainfall (Boschma, Murphy, & Harden, ) and to efficiently utilize the water resource.…”

“…A neighbouring experiment, on the same soil type but with shallower overall depth, examined the herbage production response to increasing N fertilizer application rates, reported yields of digit grass (11.4 and 15 t DM/ha), Rhodes grass (6.3 and 8.0 t DM/ha) and forage sorghum (10.9 and 15 t DM/ha) for the 2006–2007 and 2007–2008 growing seasons (Boschma et al., ). These are broadly in line with those reported here.…”

“…These are broadly in line with those reported here. However, the combination of shallower soil depth and a dry season in 2006–2007 resulted in little response to the fertilizer application rates (Boschma et al., ). In contrast, the second growing season with higher rainfall showed a greater response to higher N fertilizer application (Boschma et al., ).…”

“…However, the combination of shallower soil depth and a dry season in 2006–2007 resulted in little response to the fertilizer application rates (Boschma et al., ). In contrast, the second growing season with higher rainfall showed a greater response to higher N fertilizer application (Boschma et al., ). At our site in the wetter year of 2007–2008, the yield declined for digit grass (16.2–13.2 t DM/ha) and Rhodes grass (11.4–7.7 t DM/ha), despite greater water availability, which reflected the lower rate of applied N. Rhodes grass consistently had lower yields than digit grass, which is in keeping with it having a lower N efficiency (Boschma et al., ).…”

Optimum plant density of Digitaria eriantha for herbage accumulation and hydrological performance in a summer dominant rainfall zone

“…Subsequently, considerable attention has been given to understanding the requirements for establishment and productivity of these species. This has included investigating weed control (Lodge, Brennan, & Harden, ), seed quality (McCormick, Lodge, Boschma, & Murray, ), sowing time and depth (Lodge & Harden, ), growth rates (Boschma, Murphy, & Harden, ), response to nitrogen (Boschma, Murphy, & Harden, ; Boschma et al., ), rooting depth (Murphy, Lodge, & Brennan, 2008a), water use and rainfall efficiency (Murphy, Lodge, & Brennan, 2008b, ), and species persistence (Boschma et al., ; McCormick, McGufficke, Harden, & Ross, ). This work has helped the successful establishment of tropical pastures across the region.…”