Legume crops and pastures have a high economic value in Australia. However, legume species commonly used for grazing enterprises have been identified to produce high concentrations of phytoestrogens. These compounds are heterocyclic phenolic, and are similar in structure to the mammalian estrogen, 17β-estradiol. The biological activity of the various phytoestrogen types; isoflavones, lignans and coumestans, are species-specific, although at concentrations of 25 mg/kg of dry matter each of the phytoestrogen types affect reproductive functions in grazing livestock. The impacts upon fertility in grazing livestock such as cattle and sheep, vary greatly over length of exposure time, age and health of animal and the stress stimuli the plant is exposed to. More recently, research into the other effects that phytoestrogens may have upon metabolism, immune capacity and growth and performance of grazing livestock has been conducted. Potential new benefits for using these phytoestrogens, such as daidzein and genistein, have been identified by observing the stimulation of production in lymphocytes and other antibody cells. Numerous isoflavones have also been recognized to promote protein synthesis, increase the lean meat ratio, and increase weight gain in cattle and sheep. In Australia, the high economic value of legumes as pasture crops in sheep and cattle production enterprises requires proactive management strategies to mitigate risk associated with potential loss of fertility associated with inclusion of pasture legumes as forages for grazing livestock.

The effect of grazing of vegetative canola (Brassica napus) with sheep on crop growth and yield was investigated in two field experiments (Expts 1 and 2) in 2008 at Wagga Wagga, New South Wales, Australia. The experiments included a range of cultivars, sowing rates, and grazing periods to investigate the influence of these factors on grazing biomass, crop recovery, and grain yield. Three spring canola cultivars (representing triazine-tolerant, conventional, and hybrid types) were used in both experiments and were sown at three sowing rates and grazed by sheep for 7 days in midwinter in Expt 1, while two different grazing periods were compared in Expt 2. Supplementary irrigation was applied to Expt 1 to approximate average growing season conditions, while Expt 2 received no irrigation. Increased sowing rate produced greater early shoot biomass for grazing, but the-triazine tolerant cultivar produced less biomass than the conventional or hybrid cultivars in both experiments. Grazing reduced dry matter and leaf area by >50%, delayed flowering by 4 days on average, and reduced biomass at flowering by 22–52%. However, there was no impact of cultivar or sowing rate on the recovery of biomass and leaf area after grazing. Grazing had no effect on final grain yield under supplementary irrigation in Expt 1, but reduced grain yield under the drier regrowth conditions in Expt 2. The results demonstrate that grazing canola is feasible under average seasonal conditions in a medium-rainfall environment (400–600 mm) without yield penalty, provided the timing and intensity of grazing are matched to available biomass and anticipated seasonal water supply to support grain production. More broadly, we suggest that grain yield reductions from grazing could be avoided if suitable conditions for regrowth (residual dry matter, length of regrowth period, and adequate moisture) can generate biomass levels in excess of a target value of ~5000 kg ha–1 at flowering. This target value represents a biomass level where >90% of photosynthetically active radiation was intercepted in our study, and in other studies represents a biomass level above which there is little further increase in potential yield. Such a target provides a basis for more objective grazing management but awaits further confirmation with experimentation and modelling.

Spatial and temporal variation in soil Mn2+ was observed over a 12-month period at two field sites near Gerogery and Binalong in southern New South Wales (NSW), Australia. Three pot experiments were then conducted to emulate the range of soil Mn2+ concentrations observed in the field and to determine the effect of different concentrations on lucerne and subterranean clover seedling growth, as well as to determine the effect of heating a soil on pH and Mn2+ concentrations. Concentrations of soil Mn2+ in the surface 0.20 m varied at a given sampling date by up to 288% (2.5–9.7 µg/mL) and 183% (8.7–24.6 µg/mL) across the Gerogery and Binalong field sites, respectively. At both sites, the concentration of soil Mn2+ in a given plot also varied by up to 175% between sampling times. There was little consistency between sites for seasonal fluctuations of soil Mn2+, although in both instances, peaks occurred during months in which newly sown lucerne plants might be emerging in southern NSW. Pot experiments revealed that high concentrations of soil Mn2+ reduced lucerne seedling survival by 35%, and on seedlings that did survive, reduced shoot growth by 19% and taproot length by 39%. Elevated concentrations of soil Mn2+ also reduced subterranean clover seedling survival by up to 55% and taproot length by 25%, although there were few effects on subterranean clover in treatments other than those imposing the highest soil Mn2+ concentrations. The third pot experiment demonstrated that elevated soil temperatures led to increased soil pH and increased soil Mn2+ concentrations, attributable to a decrease in biological oxidation of soil Mn2+. This was in contrast to the commonly anticipated response of a decline in soil Mn2+concentrations as soil pH increased.

SUMMARY: The objective of the present study was to investigate live weight (LW) gain, urinary nitrogen (UN) excretion and urination behaviour of dairy heifers grazing pasture, chicory and plantain in autumn and spring. The study comprised a 35-day autumn trial (with a 7-day acclimation period) and a 28-days spring trial (with a 7-day acclimation period). For each trial, 56 Friesian × Jersey heifers were blocked into five dietary treatments balanced for their LW and breeding worth (i.e. genetic merit of a cow for production and reproduction): 1·00 perennial ryegrass–white clover pasture (PA); 1·00 chicory (CH); 1·00 plantain (PL); 0·50 pasture + 0·50 chicory (PA + CH); and 0·50 pasture + 0·50 plantain (PA + PL). A fresh allocation of the herbage was offered every 3 days with allowance calculated according to feed requirement for maintenance plus gain of 1·0 kg LW/day. In both trials, LW gain was lower on CH than other treatments. In the spring trial, UN concentration and UN excretion were lower in CH and PL than other treatments. In autumn, a higher urination frequency was observed over the first 6 h after forage allocation in CH and PA + CH than other treatments. Data from the present study indicate that feeding CH alone limited heifer LW gain. However, heifers grazing swards containing chicory (CH and PA + CH) and plantain (PL and PA + PL) had the potential to lower nitrous oxide emissions and nitrate leaching from soil compared with heifers grazing PA, by reducing N loading in urine patches.

Canola (Brassica napus L.) has recently been adopted as a dual-purpose crop (graze and grain) in the higher rainfall areas (>550 mm) of eastern Australia, but the feasibility in drier inland areas with a shorter growing season is uncertain. We modified the APSIM-Canola model by using observations from an irrigated grazing experiment, with the aim of using a simulation approach to investigate various aspects of dual-purpose canola production. Sowing opportunities, forage production for grazing and grain production were considered in the simulations, and effects of variables such as sowing date, cultivar type, plant density and nitrogen supply were investigated in simulations for 109 years of climate data from Wagga Wagga, NSW. APSIM-Canola predictions of vegetative growth and grain yield for recent varieties were inadequate when using existing parameters, but were improved by increasing the maximum leaf area parameter to reflect those of modern hybrid types. For grazed crops, APSIM-Canola overestimated the initial rate of regrowth, but accurately simulated biomass at flowering. Simulations of a range of management options to generate different pre-grazing biomass predicted that sowing before 15 May, using vigorous (hybrid) cultivars, high plant density (60–80 plants m–2) and adequate soil nitrogen, maximised biomass production. Assuming a rainfall-based sowing opportunity of 25 mm over 3 days and a minimum pre-grazing biomass of 1000 kg ha–1, grazing was possible in 53% of years, with 50% of those years providing grazing opportunities before 7 June at Wagga Wagga. Depending on stocking rate, crops could be grazed until early to mid-July, providing 400–1000 dry sheep equivalent days ha–1 of grazing, and allow regrowth to achieve a target biomass of 5000 kg ha–1 at flowering, which was required to maximise potential yield. The simulation analysis confirms significant opportunities to achieve valuable livestock grazing from canola crops sown in an early window (before May) without compromising potential yield, and the simulation framework developed can be readily applied to other regions.