W. M. Kelman

Dual-purpose canola—a new opportunity in mixed farming systems

The term dual-purpose canola describes the use of a canola crop for forage before seed production. It could potentially provide a profitable and flexible break-crop option for mixed farms, but there have been no studies to test the concept in Australia. We investigated the feasibility of using canola in this way in field experiments near Canberra, Australia, from 2004 to 2006, using European winter and mid–late maturing Australian spring canola varieties. Winter varieties sown from early March to mid-April produced 2.5–5.0 t/ha of biomass providing 0.3–3.5 t/ha of high-quality forage grazed by sheep in winter. The spring varieties produced similar amounts of vegetative biomass from April sowing but were unsuited to the earlier March sowing as they flowered in early winter and did not recover from grazing. The canola forage was readily eaten by sheep; alkane-based estimates of diet composition indicated that >85% of the organic matter intake consisted of canola. Canola forage was also highly digestible (86–88%) and Merino hoggets grew at 210 g/day from a dry matter intake of 1530 g DM/day. The canola generally recovered well when grazed in winter before bud elongation. Delays in flowering associated with heavy grazing ranged from 0 to 4 days when grazed before buds were visible, to 28 days if the crop had commenced flowering. Significant delays in flowering (>14 days) associated with winter grazing did not reduce seed yield or oil content when favourable spring conditions allowed compensatory growth. Yield loss was observed when winter and spring conditions were unfavourable for compensatory growth, or if grazing continued too late into spring (late September) irrespective of seasonal conditions. The yield loss was more than offset by the value of the grazed forage and the mean gross margin for dual-purpose canola over the four experiments was

Plant wax alkanes and alcohols as herbivore diet composition markers

240 to

Cuticular wax alkanes and alcohols used as markers to estimate diet composition of sheep (Ovis aries)

500 higher than for grain-only canola depending on the value assumed for the forage. The study indicates there is considerable scope to capture value from grazing early-sown canola crops during winter without significant, uneconomic trade-offs with seed yield. Further investigations in other medium to high rainfall environments in southern Australia are warranted.

Growth and phenology of winter wheat and oats in a dual-purpose management system

Abstract The n-alkanes in plant cuticular wax have been used as markers for estimating the species composition of herbivore diets, but the long-chain fatty alcohols (LCOH) of plant wax may also be useful. The objective of this research was to assess if LCOH contributed extra information to differentiate plant species, compared with n-alkanes only. We used 3 data sets consisting of n-alkane and LCOH concentrations of plant species occurring in pastures of New South Wales, Australia. We used Principal Component Analysis (PCA) to summarise the data for n-alkane and LCOH concentrations obtained for the species in these data sets. The first 3 principal components explained 86 to 93% and 75 to 99% of the variance in n-alkane and LCOH concentrations, respectively. Orthogonal Procrustes Rotation (OPR) was then used to compare the results of PCA conducted with n-alkane and LCOH data, with a view to establishing whether LCOH provided discriminatory information in addition to that provided by the n-alkanes. Results of OPR indicated that this was so for all 3 data sets, and suggested that the LCOH would be useful additional markers for discriminating between plant species. We tested this by using Discriminant Analysis and cross-validation procedures in 2 data sets to distinguish between defined species groups of C3 grasses, C4 grasses, clovers and Lotus spp. The discrimination between these categories and the proportion of plant species correctly classified into the defined categories was better when using n-alkanes and LCOH together, compared with alkanes alone. Our results indicate that LCOH provided additional information that could be used for distinguishing plant species as part of estimating the species composition of herbivore diets.

Grazing winter wheat relieves plant water stress and transiently enhances photosynthesis

Abstract The chemical components in plant cuticular wax can be used as markers to estimate the species composition of the diet of grazing animals. In this experiment, sheep ( Ovis aries ) grazed swards consisting of two sown species of Lotus ( L. corniculatus and L. pedunculatus ), two sown grasses ( Phalaris aquatica and Austrodanthonia richardsonii ) and volunteer annual grasses and legumes (dominated by Vulpia myuros and Trifolium spp.). The botanical composition of the sward was estimated before and after grazing over three days by four sheep. During the grazing period, samples of whole plants of the species present, plus rectal faecal samples from the sheep, were collected, freeze-dried and ground prior to the extraction of cuticular wax n-alkanes and long-chain alcohols. Purified alkanes and alcohols in samples of faeces and plants were quantified by gas chromotography. The species composition of the sheep diets was estimated by relating faecal alkane and alcohol contents to those of the plant species on offer, using the ‘EatWhat’ software package. Principal Components Analysis explained 75% of the variance in the pattern of alkane concentrations between the species on the first two axes. PCA using alcohols accounted for 68% of the variance on the first two axes and separated the Lotus species from the grasses and clovers. Comparison of the two PCA, using Orthogonal Procrustes Rotation, indicated that the long-chain alcohols contributed extra information over and above that provided by the alkanes. Discriminant analysis of alkane and alcohol concentrations enabled a clear separation of Lotus , clover and grass species groups. Using alkanes as markers, the diet consumed by sheep contained 18±1.1% Lotus , whilst using both alkanes and alcohols, the estimated Lotus content of the diet (26±1.2%) was closer to the Lotus content of the sward (31%). Diet composition estimates indicated that the Lotus component consisted mostly (>90%) of L. corniculatus . This apparent selection against L. pedunculatus may relate to the much higher condensed tannin content in that species.

Integrating dual-purpose wheat and canola into high-rainfall livestock systems in south-eastern Australia. 2. Pasture and livestock production

Dual-purpose cereal cropping is gaining acceptance among growers in mixed farming systems. Success in particular seasons depends on management decisions regarding choice of cereal species, sowing date, timing of grazing, and stocking rate. A more detailed understanding of how these factors influence the growth, phenology, and grain yield of the major cereal forages is needed to model these systems. Wheat (cvv. Whistler and Mackellar) and oats (cv. Blackbutt) were grown under dual-purpose management near Canberra, ACT, over 3 years (2004–06) in 2 crop sequences: wheat-oats-wheat and oats-wheat-wheat. In each year, crops were grazed by sheep at low (20/ha), medium (30–35 /ha), and high (40–52 /ha) grazing intensities. In the pre-grazing periods, measurements of phyllochron interval (PI), tiller development rate (TDR), and stem apex height were made. Post-grazing growth rate was determined from shoot biomass cuts taken at the end of grazing and at grain harvest. Soil moisture changes during each year were monitored to examine the pattern of soil water use under varying grazing intensities. In unusually dry periods in March–April 2004 and 2005, oats established significantly denser plant populations than wheat. In 2004, this initial advantage of oats resulted in greater feed on offer at the start of grazing than wheat, whereas in 2005, higher TDR, lower PI of wheat, and the longer duration of tillering resulted in similar amounts of feed on offer at the start of grazing. Elongation of the stem apex was more rapid in wheat than oats, indicating that wheat would be more at risk of damage during grazing. The post-grazing growth rate of wheat and oats was significantly lower than the ungrazed control in the dry spring years of 2004 and 2006, but significantly higher in the wetter spring year of 2005. While reduction in growth rate at high stocking rate was most likely caused by extreme reduction in leaf area, the causes of increases in growth rate following more lenient grazing require further investigation. In 2004 and 2005, there was no significant difference between crops or between stocking rate treatments in soil water depletion during the post-grazing period. However, in 2006, when soil moisture was not affected by rainfall in the post-grazing period, significantly more water was depleted from soil in the 0.60–1.70 m depth under low and medium stocking rate treatments than under the ungrazed control treatment. A gross margin analysis showed greater economic returns for the dual-purpose compared with a grain-only option in each year, most notably in the very dry season in 2006, when conventional practice would have been to sacrifice the grain crop to grazing or hay production.

Predicting condensed tannin concentrations in Lotus uliginosus Schkuhr using near-infrared reflectance spectroscopy

To model the impact of grazing on the growth of wheat (Triticum aestivum L.), we measured photosynthesis in the field. Grazing may affect photosynthesis as a consequence of changes to leaf water status, nitrogen content per unit leaf area (Na) or photosynthetic enzyme activity. While light-saturated CO2 assimilation rates (Asat) of field-grown wheat were unchanged during grazing, Asat transiently increased by 33–68% compared with ungrazed leaves over a 2- to 4-week period after grazing ended. Grazing reduced leaf mass per unit area, increased stomatal conductance and increased intercellular CO2 concentrations (Ci) by 36–38%, 88–169% and 17–20%, respectively. Grazing did not alter Na. Using a photosynthesis model, we demonstrated that the increase in Asat after grazing required an increase in Rubisco activity of up to 53%, whereas the increase in Ci could only increase Asat by up to 13%. Increased Rubisco activity was associated with a partial alleviation of leaf water stress. We observed a 68% increase in leaf water potential of grazed plants that could be attributed to reduced leaf area index and canopy evaporative demand, as well as to increased rainfall infiltration into soil. The grazing of rain-fed grain cereals may be tailored to relieve plant water stress and enhance leaf photosynthesis.

Liveweight gains of young sheep grazing dual-purpose wheat with sodium and magnesium supplied as direct supplement, or with magnesium supplied as fertiliser

Abstract. In south-eastern Australia, low winter temperatures often reduce pasture growth and thus winter herbage supply relative to livestock requirements. Grazing of vegetative grain crops in winter is one strategy that might overcome this feed gap. In a study with young sheep over two seasons near Canberra, ACT, we compared pasture-only grazing with three separate crop–livestock systems in which the sheep grazed long-season wheat, winter canola or a combination of these, for intervals over the period May–August. We measured forage biomass, sheep grazing days (SGD) and liveweight accumulated per ha. Crop-grazing treatments resulted in much more winter forage for grazing sheep (t DM ha–1): in 2010, one crop 2.5–3.0, two crops 3.5 v. pasture only 1; in 2011, one crop 2, two crops 3 v. pasture only 1.4. In the first season, grazing one crop resulted in ∼2000 extra SGD ha–1 and the accumulation of more liveweight per ha than in the pasture-only treatment; grazing of two crops resulted in >3500 extra SGD ha–1. Equivalent values in the second, drier season were: one crop, ∼1000 extra SGD ha–1; two crops, 2600 extra SGD ha–1. Spelling of pastures during crop grazing led to extra pasture growth, such that in each of the two seasons, 40% of the total benefit in extra SGD per ha came from the extra pasture. The results indicate that, like grazed wheat, grazed canola can provide valuable winter forage, especially when used together with wheat. The data also provide the first quantification of the effect of crop grazing on pasture spelling and subsequent pasture supply, and suggest value in the incorporation of grazing wheat and canola into grazing systems in the high-rainfall zone.

Integrating dual-purpose wheat and canola into high-rainfall livestock systems in south-eastern Australia. 1. Crop forage and grain yield

Near-infrared reflectance spectroscopy (NIRS) was used to develop equations to predict condensed tannins (CT) in greater lotus (Lotus uliginosus Schkuhr) with a precision satisfactory for the screening of genotypes in a plant breeding programme. NIRS equations were developed using both partial least squares and stepwise multiple linear regression techniques, and a wide range of mathematical treatments of the log 1/reflectance NIRS data. In general, equations developed using partial least squares regression techniques had 10–15% lower standard errors than those developed using stepwise multiple linear regression, during both calibration and prediction. Standard errors of calibration ranged from 10 to 17 g kg−1, standard errors of prediction from 12 to 17 g kg−1. These errors equate to coefficients of variation in the order of 20% The use of NIRS to predict CT in greater lotus will allow more rapid evaluation and selection of genotypes than could be achieved using butan-1-ol/HCl hydrolysis.

Breeding of an early-flowering and drought-tolerant Lotus corniculatus L. variety for the high-rainfall zone of southern Australia

In four experiments conducted in 2006–2008 near Canberra, Australia, young sheep grazed vegetative dual-purpose wheat (cv. Mackellar) while receiving either no mineral supplement or receiving extra sodium (Na) and/or magnesium (Mg). In the first two experiments, supplements were fed to the sheep whereas in Experiments 3 and 4, the extra Mg was applied to the crop just before grazing commenced, either as MgSO4 (Experiment 3, 4) or Causmag (MgO; Experiment 4). Direct supplements of Na resulted in increases of liveweight gain of 20–25% (36–42 g/day). In Experiment 2, sheep consumed significantly less of the mixed Na/Mg supplement than of salt alone (12.0 vs 24.8 g/day; P < 0.05) but still grew significantly faster (61 g/day; P < 0.05) than unsupplemented sheep. Application of supplementary Mg to the crop resulted in significant increases in forage Mg, from levels close to animal requirement (0.10% DM) to levels well above this. It also improved a range of mineral indices related to Mg status. Increases in liveweight gain occurred in response to top-dressing of the crop, but compared with feeding Mg directly to the sheep, these were transient and strongly interacted with stocking rate. Estimates of the cost of supplementation or top dressing, and of the value of the extra liveweight gain obtained, indicated that direct supplementation would be economic, but that top-dressing costs would exceed the value of the extra liveweight gain obtained.