Pastures at Shannon Vale nutrition station

Abstract

Selected sown and natural pastures on the granitic soils of Shannon Vale Nutrition Station were compared over a period of 3½ years, 1951-54. Dry matter, botanical composition, and protein yields were assessed at each of 14 consecutive sampling periods of varying length, and these are correlated with each other and with seasonal variations and grazing managements. Sown pastures were vastly superior in yields of total pasturage, legumes, edible weeds, and crude protein, as well as in their percentage of crude protein. The data explain the observed and previously reported responses in livestock health, carrying capacity and production at the Station, giving further evidence that the wasting disease "poorness of blood" was caused by starvation, primarily through lack of protein. Growth rate reached 64 and 23 pounds per acre per day on sown and natural pastures respectively, through a wet spring. The same lush pasture grew 12.5 pounds of dry matter per acre per day through winter, while natural pastures were frosted and lost bulk (-1.2 pounds of dry matter per acre per day)· Natural pastures yielded only 1928 and 1722 pounds of dry matter per acre per annum during the two successive sections over a total of 1246 days. Sown pastures in these sections gave annual dry matter production of 4273 and 4334 pounds per acre. This represents 2.2 to 2.5 times the dry matter production of natural pastures. The sown pastures produced about 2.4 times the growth of natural pastures in most 12 month periods. Winter growth of sown pastures was 2.3 to 4.1 times that from natural pastures. Statistical analyses suggested significant superiority of sown compared with natural pastures in all winters and in moist warm seasons, but the increases in yields during dry warm seasons could not be shown significant at the 5 per cent level. Most of the 14 periods were extraordinarily dry for this district, hence the results represent almost the minimum yields and minimum differences which could be expected. The driest and the second driest spring-summer seasons on record in Glen Innes were sampled during this study. Yet sown pastures were superior to natural pastures in yield throughout these droughts, and even at the end of them were offering an equal quantity of forage. Temperature, rainfall, and other environmental factors affected pasture performances differently for each pasture studied. Killing frosts and the effects of low winter temperatures have markedly reduced winter production of natural pastures. Rainfall appeared to be the dominant weather factor influencing sown pastures at Shannon Vale: wide variations occurred between the production in wet and in dry seasons. The effects of various management patterns and grazing pressures have also been evident on dry matter growth, disposal, and ungrazed residue. Close agreement was reached between the measured yearly disposal of pasturage and the expected consumption by the stock grazing the pastures. Three out of four measurements showed utilisation of more than 94 per cent of the forage offered. A moderately close agreement was achieved between measurements and the expected sheep consumption during the 3 individual periods for which comparisons were possible. Under normal stocking pressures for the Nutrition Station ungrazed residues of 800 to 1000 pounds of dry matter per acre remained on sown pastures. Larger residues were recorded after previous periods of strategically lenient stocking, but smaller residues to 300 pounds per acre always followed heavy grazings. Improved weather conditions would then fail to induce a response as strong as that after lenient grazings. Natural pastures carried smaller residues of 200 to 600 pounds per acre. Legume percentage ranged from slight to 41.7 per cent in sown pastures, being responsive to the wide range of seasonal conditions and management factorso Natural pastures rarely showed any notable legume content and exceeded 1 per cent on only three occasions - the maximum figure being only 3.2 per cent. An excess of protein content was provided by sown pastures in every season, whereas natural pasturage was deficient in protein for stock health in all but the most productive seasons, and especially throughout winter. Crude protein contents of natural pastures ranged from 4.1 to 8.1 per cent, whilst corresponding values for sown pastures varied from 7.0 to 14.4 per cent. Total yields of crude protein from sown pastures averaged 3 to 7 times those from natural pastures. In winter-time sown pastures averaged 0.6 pounds of crude protein increase per acre per day, while natural pastures, as an average, remained static in protein yield. Advantages and faults are mentioned for the cage-and-­outfield "difference" technique as applied in this study and the reliability of its data are discussed. Statistics for some aspects of the pastoral industries of the Northern Tablelands are used to show that the findings of this study and related investigations are being adopted widely by landholders. The trend, since World War II, of a change from purely wool growing to flock-breeding and further to fat-lamb production, is highlighted and discussed in relation to the rapidly expanding areas of sown pastures.