The nutritive value of Rhodes grass (Chloris gayana) when treated with CaO, NaOH or a microbial inoculant and offered to dairy heifers as big-bale silage

A series of laboratory and animal studies examined the use of chemical and biological agents to enhance the digestibility of Rhodes grass (grass) cut at 60 (young) and 100 (mature) days of regrowth and ensiled as big round bales. The treatments included an untreated control (C), a microbial inoculant (I), NaOH, CaO and NaOH plus inoculant (NaOH + I). Inoculant was grown anaerobically, using a starter culture of rumen fluid from cattle given Rhodes grass. Treatments C, 1, NaOH, NaOH + I, were offered separately to twelve dairy heifers, in a 3 X 4 randomized complete block design, repeated twice for each grass silage. C and I had substantial mould growth, compared with no visible mould in NaOH or NaOH + 1. CaO treatment was effective in preventing mould growth, but had little effect on the chemical composition and in sacco digestibility of mature grass silage. NaOH reduced NDF content and increased in sacco digestibility (P < 0.05) but not the in vivo digestibility (P > 0.05) of both mature- and young-grass silage. The effects of other treatments on nutritive value were non-significant at both stages of maturity. NaOH increased the intake of mature-grass silage by 24-26% (P < 0.05), but had little effect on the intake of young-grass silage (P > 0.05). Treatment I consistently reduced grass silage intake (P < 005) for young-grass silage. The findings of these studies show that treating mature Rhodes grass with NaOH will improve its nutritive value and reduce mould growth in conserved herbage. However none of the treatments in this study had any consistently positive effects on the in vivo nutritive value or storage quality of young-grass silage.

Effect of leucaena supplementation level, and provision of urea, on utilisation by sheep of Rhodes grass hay

Tarramba leucaena (Leucaena leucocephala cv. Tarramba) foliage had per kilogram dry matter, 169 g protein and 29.8 g condensed tannins. Its value as a supplement, given either with or without urea, to sheep given a low-quality Callide Rhodes grass (Chloris gayana cv. Callide) hay was studied. Six rumen fistulated sheep (mean +/- s.d. liveweight, 34 +/- 1.4 kg) were used to compare 6 dietary treatments in an incomplete latin square design. Rhodes grass hay was given ad libitum either alone, or with urea 7 g/day (U), or with leucaena 150 g/day (L150), or leucaena with urea (L150U), or leucaena 300 g/day (L300), or leucaena with urea (L300U). Digestible organic matter intake was increased significantly by leucaena supplementation although digestibility of the whole diet did not alter. Rumen fluid ammonia-N was not altered by leucaena supplementation, but was increased by urea. This suggests that Tarramba foliage protein has some resistance to ruminal degradation. Liquid and solids passage rates were not affected by the treatments. Microbial nitrogen supply to the intestine (g/day), and the efficiency of microbial nitrogen synthesis (g/kg organic matter apparently digested in the rumen), were increased by leucaena supplementation (P

Seed dormancy mechanisms in warm season grass species

Available evidence suggests that there are at least two locations for dormancy mechanisms in primary dormant seeds: mechanisms based within the embryo covering structures, and mechanisms based within the embryo. Mechanisms within the covering structures may involve mechanical, permeability and chemical barriers to germination. Mechanisms within the embryo may involve the expression of certain genes, levels of certain plant growth regulators, the activity of important respiratory pathways or the mobilisation and utilisation of food reserves. In addition, some embryos may be too immature to germinate immediately and must undergo a further growth phase before germination is possible. An individual species could have one or several of these various dormancy mechanisms and these mechanisms need to be understood when selecting treatments to overcome dormancy. The way in which certain dormancy breaking agents are thought to work is discussed and practical applications of such agents in field situations are explained.

DNA sequence variation in the ITS-1 rDNA subunit and host relationships in sorghum midge, Stenodiplosis sorghicola (Coquillett) (Diptera : Cecidomyiidae), in Australia

Sequence variation in the internal transcribed spacer (ITS-1) ribosomal DNA subunit was examined for sorghum midge obtained from introduced and native hosts in south-eastern and central Queensland. No variation was observed relative to host plant or geographical distance for midges collected from two introduced hosts, grain sorghum (Sorghum bicolor ) and Johnson grass (S. halepense ); however, sequence differences were observed between midges from introduced and native hosts and among midges from a single native host, slender bluegrass (Dichanthium affine ). No evidence was observed of introduced midges on native hosts, or vice versa. These results agree with previously hypothesised host distributions for native and introduced midges in Australia, and expand the sample of introduced hosts to include Johnson grass. They suggest that Stenodiplosis sorghicola , the principal midge infesting grain sorghum, is also the most common species on Johnson grass. This confirms that Johnson grass plays a role in the population dynamics of S. sorghicola and suggests that midges originating from Johnson grass may influence levels of infestation in grain sorghum.

The effects of level of dietary protein on the milk production and rumen physiology of dairy cows fed a diet based on a tropical grass hay

zFour rumen-fistulated, multiparous Holstein-Friesian cows in early lactation were offered mixed diets based on rhodes grass hay (Chloris gayana) cv. Callide containing 13, 14, 15 or 16% crude protein (CP) on a dry matter basis, in a 4 x 4 latin square design. The estimated undegradable protein concentration in these diets was similar with rumen degradable protein concentration varying. Cows fed a diet containing 13% CP had lower (P = 0.07) milk yields than cows in other treatments (20.4 vs 21.9, 22.0 and 22.2 L/d for 13, 14, 15 and 16% CP, respectively). A positive linear relationship was found (P = 0.06) between organic matter intake and dietary CP%. There were negative linear relationships between dietary CP% and digestibilities of dry matter (P = 0.09), organic matter (P = 0.06) and neutral detergent fibre (P = 0.02). Feeding a diet containing 13% CP resulted in significantly lower (P = 0.001) molar proportions (%) of rumen valerate in comparison with other treatments. The molar proportions of isovalerate differed (P = 0.001) between treatments (0.66, 0.78, 0.89 and 1.04%) for 13, 14, 15 and 16% CP, respectively). Dietary protein level had no effect on rates of passage, in situ digestion of rhodes grass hay or ratios of allantoin: creatinine in urine. These data showed that increasing the dietary CP concentration of lactating cows fed diets based on rhodes grass hay increased intakes and not significantly improved at dietary CP concentrations above 14% DM.

Nitrate-nitrate toxicity in cattle and sheep grazing Dactyloctenium radulans (button grass) in stockyards

Hungry cattle and sheep introduced to stockyards containing a dominant or pure growth of Dactyloctenium radulans (button grass) suffered acute nitrate-nitrite toxicity in four incidents in inland Queensland between 1993 and 2001. Deaths ranged from 16 to 44%. Methaemoglobinaemia was noted at necropsies in all incidents. An aqueous humour sample from one dead steer contained 75 mg nitrate/L and from one dead sheep contained 100 mg nitrate and 50 mg nitrite/L (normal = ca 5 mg nitrate/L). Both lush and dry button grass were toxic. The nitrate content of button grass from within the stockyards ranged from 4.0 to 12.9% as potassium nitrate equivalent in dry matter and from outside the stockyards ranged from

Seasonal patterns of growth, dehydrins and water-soluble carbohydrates in genotypes of Dactylis glomerata varying in summer dormancy

Background and Aims Summer dormancy in perennial grasses has been studied inadequately, despite its potential to enhance plant survival and persistence in Mediterranean areas. The aim of the present work was to characterize summer dormancy and dehydration tolerance in two cultivars of Dactylis glomerata (dormant 'Kasbah', non-dormant 'Oasis') and their hybrid using physiological indicators associated with these traits. Methods Dehydration tolerance was assessed in a glasshouse experiment, while seasonal metabolic changes which produce putative protectants for drought, such as carbohydrates and dehydrins that might be associated with summer dormancy, were analysed in the field. Key Results The genotypes differed in their ability to survive increasing soil water deficit: lethal soil water potential (ψ(s)) was -3(.)4 MPa for 'Kasbah' (although non-dormant), -1(.)3 MPa for 'Oasis', and -1(.)6 MPa for their hybrid. In contrast, lethal water content of apices was similar for all genotypes (approx. 0(.)45 g H2O g d. wt(-1)), and hence the greater survival of 'Kasbah' can be ascribed to better drought avoidance rather than dehydration tolerance. In autumn-sown plants, 'Kasbah' had greatest dormancy, the hybrid was intermediate and 'Oasis' had none. The more dormant the genotype, the lower the metabolic activity during summer, and the earlier the activity declined in spring. Decreased monosaccharide content was an early indicator of dormancy induction. Accumulation of dehydrins did not correlate with stress tolerance, but dehydrin content was a function of the water status of the tissues, irrespective of the soil moisture. A protein of approx. 55 kDa occurred in leaf bases of the most dormant cultivar even in winter. Conclusions Drought avoidance and summer dormancy are correlated but can be independently expressed. These traits are heritable, allowing selection in breeding programmes.

Hydraulic properties of layered soils influence survival of Rhodes grass (Chloris gayana Kunth.) during water stress

Survival of vegetation on soil-capped mining wastes is often impaired during dry seasons due to the limited amount of water stored in the shallow soil capping. Growth and survival of Rhodes grass (Chloris gayana) during soil drying on various layered capping sequences constructed of combinations of topsoil, subsoil, seawater-neutralised residue sand and low grade bauxite was determined in a glasshouse. The aim was to describe the survival of Rhodes grass in terms of plant and soil water relationships. The soil water characteristic curve and soil texture analysis was a good predictor of plant survival. The combination of soil with a high water holding capacity and low soil water diffusivity (e.g. subsoil with high clay contents) with soil having a high water holding capacity and high diffusivity (e.g. residue sand) gave best survival during drying down (up to 88 days without water), whereas topsoil and low grade bauxite were unsuitable (plants died within 18-39 days). Clayey soil improved plant survival by triggering a water stress response during peak evaporative water demand once residue sand dried down and its diffusivity fell below a critical range. Thus, for revegetation in seasonally dry climates, soil capping should combine one soil with low diffusivity and one or more soils with high total water holding capacity and high diffusivity.

The effect of copper toxicity on the growth and root morphology of Rhodes grass (Chloris gayana Knuth.) in resin buffered solution culture

A solution culture experiment was conducted to examine the effect of Cu toxicity on Rhodes grass (Chloris gayana Knuth.), a pasture species used in mine-site rehabilitation. The experiment used dilute, solution culture to achieve external nutrient concentrations, which were representative of the soil solution, and an ion exchange resin to maintain stable concentrations of Cu in solution. Copper toxicity was damaging to plant roots, with symptoms ranging from disruption of the root cuticle and reduced root hair proliferation, to severe deformation of root structure. A reduction in root growth was observed at an external Cu concentration of < 1 mu M, with damage evident from an external concentration of 0.2 mu M. Critical to the success of this experiment, in quantitatively examining the relationship between external Cu concentration and plant response, was the use of ion exchange resin to buffer the concentration of Cu in solution. After some initial difficulty with pH control, stable concentrations of Cu in solution were maintained for the major period of plant growth. The development of this technique will facilitate future investigations of the effect of heavy metals on plants.