Relationships between sward characteristics, grazing behaviour and growth of Hereford steers were studied on nitrogen-fertilized (378 kg ha-1 yr-1) Setaria anceps cv. Nandi and Digitaria decumbens swards continuously stocked at 4.3, 6.2 and 8.0 beasts ha-1 during five periods over 2 years. Availability of herbage, as measured by bite size, and nitrogen content and in vitro digestibility of herbage in the top of the swards were the two most important factors influencing the performance of steers. The relative importance of these factors varied between seasons, between stocking rate treatments and to a lesser extent between pasture species. The highest growth rates were measured on the leniently stocked pastures because steers were able to harvest feed easily (a large bite size) and could more readily select the more nutritious plant parts from the top of the sward. The swards were highly heterogeneous, and numerical analysis of data showed that at the same herbage yield, spatial distribution of herbage (leaf bulk density and leaf to stem ratio) and the nutritive value (in vitro digestibility and nitrogen content) of herbage greatly influenced the growth of steers. Cattle were unable to satisfy their feed requirements on some high quality but low-yielding swards, despite increasing grazing time to compensate for the small bites prehended (up to 707 min in 24 hr in spring). Consequently nitrogen and digestibility contents of extrusa samples were at times poor indicators of performance.
Using seedling characters, the relationships of 16 taxa of the informal series Ovatae of Eucaiyptus were investigated. The method of multidimensional unfolding proved useful in determining ancestral states of different characters and testing for conformity amongst characters when outgroup comparison was not possible. The analyses included Wagner trees, a branch and bound algorithm (which produced the shortest trees) and an additive similarity tree. Neighbour relationships were examined using a network procedure (TWONET). The results suggested that series Ovatae is a paraphyletic group, although one subgroup, approximately equivalent to subseries Ovatinae, is probably monophyletic. The biogeography and ecology of the taxa support this conclusion. A broader study of section Maidenaria is recommended before taxonomic revision.
A detailed study has been carried out in four regions in the subtropics of Eastern Australia to determine the relationship between the Southern Oscillation Index (SOI) and subsequent seasonal rainfall. The period studied was from 1915 to 1991 for 3-monthly periods of spring (SON), summer (DJF), autumn (MAM) and winter (JJA). The 3-monthly prior SOI values were plotted against seasonal rainfall of the four regions and four seasons. These data were widely scattered but with a linear trend showing increased seasonal rainfall as the SOI increased. Linear trends were plotted for each season and region. Comparisons were made between the use of the ACE algorithm, which transforms the SOI and rainfall data, and the use of linear trends. Polynomials were used to calculate equations for each region and season, but only spring and summer produced satisfactory ACE functions. Estimates were made of spring and summer rainfall relative to prior SOI values for each region. While the SOI as a predictor of rainfall broadly estimates spring and summer rainfall, this variable has limited usefulness on its own. One of the options available with the ACE program is that additional independent variables can be added as required. Current research suggests that sea surface temperature data from specific ocean areas surrounding the Australian continent is the most useful additional variable at present. However the complexity of such an analysis is greatly increased.
The percentage frequency of all herbaceous species in a native pasture oversown with S. humilis (T.S.) was measured at the beginning and end of an eight-year grazing experiment. Treatments imposed were three levels of molybdenized superphosphate (nil; 125 kg ha-1 annually; 250 kg ha-1 annually plus an extra 250 kg ha-1 initially) in factorial combination with four stocking rates and two sowing methods for T.S. (ground sowing into spaced cultivated strips or aerial sowing). Stocking rates were gradually increased during the experiment and for the last three years overlapping ranges were used for the three fertilizer levels; the overall range was then from 0.55 to 1.65 beast ha-1. Treatments did not induce any major changes in the proportions of native species in the pasture. Heteropogon contortus remained dominant and its frequency increased in all treatments. Of the total of 113 species recorded, only 18 reached 10 per cent frequency in at least one paddock on one occasion. Several of these showed statistically significant changes in response to treatment, but their relative importance was not greatly changed. Examination of the results by principal co-ordinate and canonical analysis, showed that the first vectors of the two data sets were highly correlated, indicating that the major control on floristic composition was not changed by oversowing with T.S. or by the treatments imposed. Treatment effects dominated in the second and third vectors in the final year. The controlling vector was found to be highly correlated with soil calcium, potassium, total exchange capacity and organic carbon, but the basis for the correlations remains undetermined.
The influence of six grazing and three mowing treatments on the botanical composition of lucerne (Medicago sativa cv. Hunter River) pastures was studied at the end of a six-year experiment on black earth in southern Queensland. Rest intervals of 32-60 d were combined with grazing durations of 4, 8 or 16 d, or with mowing. Sheep were used for grazing at a year round rate equivalent to 20/ha. Frequency of occurrence of all species and their relative herbage yield contribution were estimated in autumn and spring of the last two years. Seventy-four species were recorded, but only 17 occurred in more than 5% of grazed quadrats. Survival of lucerne, the only sown species, was good (Leach 1979a); it occurred in about 70% of quadrats but its relative yield ranged from 8 to 75%. Chloris gayana was the principal volunteer perennial grass, especially in treatments grazed for short periods (4 d) where its frequency ranged from 26 to 49% and the corresponding relative yield totals from 26 to 33% in the final spring. The volunteer species most characteristic of particular treatments were Dichanthium spp. and Chloris virgata in autumn, and Malvastrum coromandelianum, annual Medicago spp. and Trifolium repens in spring. Grazing duration or mowing influenced botanical composition more than changes in resting interval. This mainly reflected the intensity of utilization rather than grazing duration per se. Opportunities for controlling volunteer species through grazing management will be limited by compensatory responses between species. However, management should aim to ensure adequate grazing of both the lucerne and the volunteer species.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.
hi@scite.ai
10624 S. Eastern Ave., Ste. A-614
Henderson, NV 89052, USA
Copyright © 2024 scite LLC. All rights reserved.
Made with 💙 for researchers
Part of the Research Solutions Family.