Effects of grazing method and fertiliser inputs on the productivity andsustainability of phalaris-based pastures in Western Victoria

Abstract

The effects of combinations of different fertiliser rates and grazing methods applied to phalaris-based pastures on an acid, saline, yellow sodosol on the Dundas Tablelands of western Victoria (mean annual rainfall 623�mm) were measured from 1997 to 2000. The objective was to help identify management systems that improve phalaris growth and persistence, water use, and animal production, and thereby the productivity and sustainability of grazing systems. Pastures were either set stocked with low [mean 6.4 kg phosphorus (P)/ha.year] or high (mean 25 kg P/ha.year) fertiliser rates, or rotationally grazed with high fertiliser (mean 25 kg P/ha.year). Rotational grazing was implemented as either a simple '4-paddock' system (fixed rotation length), or a more intensive system where rotation length varied with pasture growth rate. Unreplicated paddocks of volunteer pasture (dominated by onion grass and annual grass weeds) receiving an average of 8 kg P/ha.year were also monitored. All treatments were stocked with spring-lambing Merino ewes. Stocking rate was an emergent property of each treatment, and was driven by pasture quality and availability. Total pasture herbage accumulation ranged from 7150 to 9750 kg DM/ha.year and was significantly lower on the set-stocked, low-fertility treatment than on all other treatments. A significant treatment.day effect in the spline analysis of herbage mass was explained by a trend toward higher pasture mass in the rotationally grazed treatments than set-stocked treatments from the break of season until mid-spring. Rotational grazing led to significantly higher phalaris herbage accumulation than set stocking (mean 3680 v. 2120 kg DM/ha.year), but significantly lower subterranean clover herbage accumulation (1440 v. 2490 kg DM/ha.year). Despite the stronger growth of deep-rooted phalaris in the rotationally grazed treatments, maximum soil water deficits at the end of summer differed only slightly between treatments, with the difference between driest and wettest treatments amounting to only 14 mm. Summer growth of phalaris was apparently insufficient to generate significant differences in soil water extraction at depth, even when phalaris content was increased by rotational grazing, and re-wetting of the soil profile occurred at a similar rate for all treatments. Rotationally grazed treatments supported higher stocking rates than set-stocked treatments at high fertiliser rates (mean 14.9 v. 13.7 ewes/ha), but apparent losses in pasture feeding value due to lower legume content under rotational grazing meant that there were few significant differences between treatments in lamb production per hectare. The experiment showed that grazing method can have a substantial and rapid effect on pasture botanical composition. There are clear opportunities for producers to use temporal and spatial combinations of set stocking and rotational grazing to manipulate herbage mass and pasture composition within broad target ranges for achieving both animal production (e.g. high per-head animal performance) and sustainability (e.g. persistence of perennial grasses) objectives. Rigid application of either set stocking or rotational grazing imposes limitations on both pasture and animal production, and neither grazing method will optimise system performance under all conditions. The experiment also demonstrated that management and land-use changes that have much greater potential to increase water use than those examined here will be needed to ensure the sustainability of pasture systems in the high rainfall zone of western Victoria.

The effects of pasture inputs and intensive rotational grazing on superfine wool production, quality and income

“…At the commencement of the trial, the target stocking rates set for the farmlets were 7.5 dry sheep equivalents (DSE)/ha for farmlet B (considered by Cicerone members to be a typical stocking rate for the area) and 15 DSE/ha for both farmlets A and C. In spite of these targets being set at the beginning of the trial, it was agreed that stocking rate would be an emergent property of each farmlet in common with the approach of other researchers (Chapman et al 2003). It is important to point out that the grazing management treatments examined here represented two different forms of rotational grazing: one flexible (farmlets A and B) and the other intensive (farmlet C).…”

“…Graham et al (2003) concluded that rotational grazing resulted in lower per head performance. Many researchers agree that rigid and inflexible grazing methods can restrict both animal and plant production (Norton 1998;Warn et al 2002;Chapman et al 2003;Graham et al 2003) but the size of the effect depends on seasonal conditions. Warn et al (2002) compared several grazing management treatments and concluded that optimum management depended on flexible, not fixed grazing intervals, based on the rate of plant growth; they also found no significant effect of grazing system or fertiliser level on wool cut per head or wool quality.…”

Integrated overview of results from a farmlet experiment which compared the effects of pasture inputs and grazing management on profitability and sustainability

“…The Cicerone experiment compared different grazing management systems to those studied by Chapman et al (2003). Whereas Chapman et al (2003) compared low and high rates of fertiliser application (6.4 and 25 kg P/ha.year, respectively), the Cicerone farmlet experiment was managed to achieve either moderate or high levels of soil fertility, based on soil tests.…”

“…Whereas Chapman et al (2003) compared low and high rates of fertiliser application (6.4 and 25 kg P/ha.year, respectively), the Cicerone farmlet experiment was managed to achieve either moderate or high levels of soil fertility, based on soil tests. For comparison, the annual rates of fertiliser applied to farmlets B and C were~4.9 and 4.3 kg P/ha, respectively, whereas farmlet A received~13.1 kg P/ha.year (Guppy et al 2013).…”

“…Farmlet C also experienced similar low levels of green herbage and digestibility to those on farmlet B but, because only a small proportion of the farmlet was available to the grazing animals at any one time, the high stock density resulted in intense competition for, and rapid depletion of green herbage during each brief grazing event (Shakhane et al 2013c). Chapman et al (2003) argued that the rigid application of grazing management regimes can result in pastures of lower quality. In rotationally grazed systems, there are compromises and trade-offs that occur between pasture and animal production such as the lower legume levels and lower levels of per-head and per-hectare production (Saul and Chapman 2002).…”