Silver Grass Research Articles

Genetic variability of natural populations of silver carp, bighead carp and grass carp in the Yangtze River

Genetic variability of natural populations of silver carp, bighead carp and grass carp in the Yangtze River

Seasonal changes in the concentrations of copper, molybdenum and sulfur in pasture plants

Seasonal changes in the concentrations of copper, molybdenum and sulfur in subterranean clover (Trifolium subterraneum), silver grass (Vulpia sp.), Wimmera ryegrass (Lolium rigidum), and capeweed (Arctotheca calendula) growing on lateritic podzolic soils were measured in glasshouse and field studies. The effects of varying soil temperature and water content on the concentrations of copper, molybdenum and sulfur in subterranean clover on a lateritic podzolic soil and a calcareous sand were also investigated. Similar seasonal patterns in plant composition were observed in the glasshouse and the field. The concentration of molybdenum tended to remain constant throughout the season, but that of copper and sulfur declined from autumn to spring; the decline was more rapid in the grasses than in subterranean clover and capeweed. Subterranean clover had higher concentrations of copper and sulfur but lower molybdenum than silver grass or Wimmera ryegrass. Capeweed contained more copper and molybdenum but less sulfur than subterranean clover. The concentrations of molybdenum and sulfur were similar in capeweed and the grasses. lncreasing soil temperature from 12 to 22�C increased the dry matter production and the concentrations of copper and molybdenum (but not sulfur) in subterranean clover on both soils. lncreasing soil water content slightly increased dry matter production and the concentration of molybdenum but had no effect on the concentration of copper and sulfur in subterranean clover. The results are discussed in relation to the health of grazing animals.

Effect of time of joining and rate of stocking on the production of Corriedale ewes in southern Victoria. 3. Wool growth and the composition and availability of pasture

A study was made during a three year period (1 968-1 970) of wool production by a flock of 540 ewes grazing annual pasture at Werribee, Victoria. The ewes were stocked at three rates (5, 7 1/2 and 10 ewes ha-1) and lambed between July 6 and August 20 or between September 10 and October 29 each year. Fibre diameter and length of wool samples were measured in 1968, 1969 and 1970 ; in 1970 growth of greasy wool was calculated from staples of dye-banded wool. Wool growth was reduced in all ewes during late pregnancy and early lactation but was not affected during late lactation in ewes lambing in September. The proportion of tender fleeces from all ewes was greater in 1970 and the weight of fleeces from only those ewes bearing single lambs was less in all years for ewes lambing in July than for ewes lambing in September. More ewes were barren and fewer ewes had twins in July and consequently the mean fleece weights of all ewes from both groups were similar. Fleeces from ewes stocked at 10 ha-1 were lighter, shorter and finer than fleeces from ewes stocked at 5 and 7 1/2 ha-1, but the proportion of tender fleeces did not differ between the groups. Wool production of ewes stocked at 5 and 7 1/2 ha-1 increased from 1968 to 1970, whereas that of ewes at 10 ha-1 did not. This was associated with differences in pasture availability and composition. At 10 ewes ha-1 less pasture was present in winter and spring in 1970 than in 1968, whereas at the other stocking rates it was greater. In 1970 the density of weeds in autumn was greater and in spring more silver grass (Vulpia spp.) and less brome grass (Bromus spp.) was available at the high stocking rate.

Evaluation of five Mediterranean annual pasture species during early growth

Pasture factors causing differences in the liveweight gain of sheep stocked at 10 sheep ha-l on continuously grazed swards of five annual species were examined during autumn and early winter. Differences in liveweight gain were due to the availability of the pasture species for prehension by grazing sheep, and depended on the weight of pasture offered and also on the growth form of the grazed plants. Subterranean clover and the volunteer species, silver grass and erodium, rapidly assumed a prostrate form under continuous grazing, thereby restricting apparent intake. Wimmera ryegrass changed less in growth form in response to grazing and for this reason liveweight gain on ryegrass in autumn was better than on clover, silver grass, and erodium. These species differences were reflected in the "critical" weight of herbage required for sheep to maintain their liveweight. Critical weight was lowest in the erect-growing Wimmera ryegrass (c. 130 kg ha-l) and highest (635 kg ha-l) in the prostrate erodium.

The comparative applied phosphate requirements of eight annual pasture species

The effects of a wide range of applied phosphate levels were compared on eight annual pasture species. Marked differences were found between species in response by tops, roots, or whole plant, and in top/root ratio. Different forms of yield response curve were given by the non-legumes, the clovers, and the lupin. At an early growth stage cape-weed, the three clovers, and erodium were highest in phosphorus requirement for near-maximum yield. At the full flowering stage, species ranked in the following decreasing order of requirement: cupped clover > rose clover > subterranean clover > lupin > erodium = cape-weed > Wimmera ryegrass = silver grass. Yields and phosphorus concentrations are compared in relation to applied phosphorus levels. In the early vegetative stage, all species needed at least 0.7% phosphorus in the tops for maximum yield, but by flowering this requirement had fallen to very much lower levels. It is suggested that differences between the species in response to applied phosphate are large enough to influence strongly the botanical composition of pasture and its fertilizer requirements.

Root distribution in a deep sand and its relationship to the uptake of added potassium by pasture plants

The distribution of roots and the uptake of 42K from various depths in soil were studied in glasshouse and field experiments on 12 temperate annual pasture species. Root/top weight ratios were mostly higher in grasses than in legumes or herbs. This ratio decreased with increasing maturity of the plants. The concentration of roots under field swards decreased exponentially with depth, from 10 cm downwards. Large differences in root distribution were noted between species. The most shallow-rooted were lotus, subterranean clover, and silver grass. The deep-rooted species were cape-weed, erodium, oats, lupins, and serradella. Some ecological implications of these differences in rooting depth are discussed. The effective rooting depth in the field was correlated with root penetration rates measured on young plants. The possibility of using root penetration rate as a means of predicting potential rooting depth is discussed. All species had a high proportion of their roots in the top 10 cm of soil and took up most 42K from this layer. As the depth increased, both the concentration of roots in the soil and the amount of potassium absorption decreased. The amount of roots at the sites of 42K placement was closely related to both the concentration and the total amount of 42K in the tops.

The effect of seed potassium on emergence and root developent of seedlings in potassium-deficient sand

Seeds of silver grass and cape-weed contained so little potassium that the roots of these species could only penetrate a highly potassium-deficient sand to a depth of 3 or 4 cm. By contrast, lupin seeds contained enough potassium to allow root development to a depth of at least 90 cm. The behaviour of other species studied was intermediate between these extremes. With seeds low in total potassium, evidence was obtained of a beneficial effect of applied potassium on seedling emergence. A study of seeds varying in total potassium from 1 µg to more than 20,000 µg showed that most of the variation in total seed potassium was due to variation in seed size, potassium concentration in the seeds being relatively unimportant. The possibility of improving the field establishment of seedlings on potassium deficient soils by increasing the potassium content of the seeds is discussed.