Pattern Of Pasture Production Research Articles

Detection of historical changes in pasture growth and attribution to climate change

Few studies consider historical trends in biological systems in relation to changes in climate. These detection and attribution studies are particularly challenging in agricultural systems where other factors (such as management) are changing over time. Here we consider changes in pasture yield (net herbage accumulation (NHA)) over the period 1960�2004 in a dataset from a trial in New Zealand where management (grazing protocol and fertiliser application) was constant over time. We used 2 approaches: a statistical approach looking for trends in, and correlations between, NHA and climate variables and a process-based modelling approach where combinations of vari- ables were held constant at their starting values or allowed to change with time enabling us to iso- late the impact of individual factors. There was a significant positive trend for NHA in spring over the period and positive trends in rainfall and atmospheric CO2 concentration; soil nitrogen (N) also increased over time. The statistical approach was useful for identifying trends but was unable to resolve the driving variables. Modelling identified CO2, soil properties and their interaction as the most influential variables. The calculated impact of CO2 was a 0.21% increase in NHA ppm CO2 �1 ; this compares to a value of 0.19% from a FACE (free air carbon dioxide enrichment) experiment with a similar type of management and pattern of pasture production. The results instill confidence in experimental estimates of the CO2 fertilisation effect, particularly at low levels of CO2 enrich- ment, and provide evidence that climate change impacts are already in progress.

Effects of phosphorus fertiliser and rate of stocking on the seasonal pasture production of perennial ryegrass-subterranean clover pasture

The response of pastures based on Lolium perenne L. and Trifolium subterraneum L. to single superphosphate was assessed at Hamilton, Victoria, by measuring the growth of pastures during winter, spring, and summer over 7 years from 1979 to 1987. The seasons were defined by the pattern of pasture production, rather than by calendar months. Winter was the period of constant growth rate following the autumn rain; spring was the period of accelerating growth rate until growth rate changed abruptly following the onset of dry summer weather. Pastures were grazed with sheep at a low, medium, or high grazing pressure, corresponding generally to stocking rates of 10, 14, or 18 sheep/ha. At each level of grazing pressure, single superphosphate was applied at 5 rates from 1979 to 1982; the highest rate, expressed as elemental phosphorus (P), was reduced from 100 to 40 kg/ha during this time. In addition there was an unfertilised treatment. In 1984, fertiliser was applied at 6 rates from 4 to 40 kg P/ha. No fertiliser was applied in the remaining years, including 1983. Pasture production was measured from 1979 to 1982 and from 1985 to 1987. Total pasture dry matter (DM) accumulation per year at the highest stocking rate was less than the other treatments in 4 of the years. Averaged over all years and fertiliser treatments, the annual net production was 10·1, 10·1, and 9·0 t DM/ha (P < 0·05) for plots grazed at low, medium, and high stocking rates, respectively. The amount of fertiliser required to reach a given proportion of maximum yield response did not vary between winter and spring in any year, but the greater potential yield in spring (P < 0 ·001) meant that as more fertiliser was applied, the disparity between pasture grown in winter and pasture grown in spring increased. Differences in this disparity between extreme levels of P ranged from 1·4 t DM/ha in a drought to about 7 t DM/ha in a good season. The implications for managing farms when pastures are fertilised at higher rates than currently practised by district farmers are that systems of animal production with a requirement for plentiful good quality pasture in spring, such as ewes lambing in spring, should be used. The benefit of spring lambing over autumn lambing was supported when the 2 systems were compared over 26 years using the GrassGro decision support system. Well fertilised pasture systems will also allow more scope for conserving pasture as hay or silage, and increase opportunities for diversification in the farming enterprise, such as spring-growing crops.

Corrigendum to: Effects of phosphorus fertiliser and rate of stocking on the seasonal pasture production of perennial ryegrass-subterranean clover pasture

The response of pastures based on Lolium perenne L. and Trifolium subterraneum L. to single superphosphate was assessed at Hamilton, Victoria, by measuring the growth of pastures during winter, spring, and summer over 7 years from 1979 to 1987. The seasons were defined by the pattern of pasture production, rather than by calendar months. Winter was the period of constant growth rate following the autumn rain; spring was the period of accelerating growth rate until growth rate changed abruptly following the onset of dry summer weather. Pastures were grazed with sheep at a low, medium, or high grazing pressure, corresponding generally to stocking rates of 10, 14, or 18 sheep/ha. At each level of grazing pressure, single superphosphate was applied at 5 rates from 1979 to 1982; the highest rate, expressed as elemental phosphorus (P), was reduced from 100 to 40 kg/ha during this time. In addition there was an unfertilised treatment. In 1984, fertiliser was applied at 6 rates from 4 to 40 kg P/ha. No fertiliser was applied in the remaining years, including 1983. Pasture production was measured from 1979 to 1982 and from 1985 to 1987. Total pasture dry matter (DM) accumulation per year at the highest stocking rate was less than the other treatments in 4 of the years. Averaged over all years and fertiliser treatments, the annual net production was 10·1, 10·1, and 9·0 t DM/ha (P < 0·05) for plots grazed at low, medium, and high stocking rates, respectively. The amount of fertiliser required to reach a given proportion of maximum yield response did not vary between winter and spring in any year, but the greater potential yield in spring (P < 0 ·001) meant that as more fertiliser was applied, the disparity between pasture grown in winter and pasture grown in spring increased. Differences in this disparity between extreme levels of P ranged from 1·4 t DM/ha in a drought to about 7 t DM/ha in a good season. The implications for managing farms when pastures are fertilised at higher rates than currently practised by district farmers are that systems of animal production with a requirement for plentiful good quality pasture in spring, such as ewes lambing in spring, should be used. The benefit of spring lambing over autumn lambing was supported when the 2 systems were compared over 26 years using the GrassGro decision support system. Well fertilised pasture systems will also allow more scope for conserving pasture as hay or silage, and increase opportunities for diversification in the farming enterprise, such as spring-growing crops.

Effects of soils, fertilizers and stocking rates on pastures and beef production on the Wallum of South-East Queensland. 4. Budgetary appraisals of fertilizer and stocking rates

Comparative budgeting techniques have been applied to the results of a grazing experiment in which the effects of different stocking rates and maintenance levels of fertilizer were examined. The experiment was carried out on grass/legume pastures in the coastal lowlands of south-east Queensland. The economic appraisal is of an investment project based on fattening purchased store cattle. Extrapolative trends have been fitted to the pattern of pasture production emerging from the first six years of an experimental period, to enable the life of the project to extend over a twenty year period. The recent sharp increases in the price of superphosphate and potassium fertilizer have had a marked effect on intensive beef production on improved pastures which is illustrated in this analysis. Pasture maintenance costs (principally fertilizer inputs) appear as the largest component of annual operating costs in most systems. The budgets indicate that at July 1973 fertilizer prices the positive internal rates of return of the various grazing systems range from 4.2 per cent to 13.2 per cent at a beef price of $0.77 kg-1 dressed weight. The highest return was obtained from a system in which 250 kg ha-1 single superphosphate and 63 kg ha-1 potassium chloride were applied annually and at a stocking rate of 1.65 beasts ha-1. These returns are reduced to a high of 10.4 per cent when 1974 fertilizer prices are incorporated. At beef prices of $0.66 kg-1, all systems but one were found to have negative internal rates of return. Assuming beef prices of $0.88 kg-1, most treatments were associated with positive internal rates of return, generally well above 10 per cent, ranging up to 20 per cent. Most of the calculations, by excluding land values from the budgeted cash flows, assume that unimproved land is already available at no charge to the investor. A series of supplementary budgets indicate the level of returns that could be expected if unimproved land commanded values of up to $200 ha-1.

Animal production from a Sorghum almum pasture in south-east Queensland

A grazing experiment on Sorghum almum pastures, one of which received 200 lb nitrogen an acre a year, as urea, was carried out at Lawes in south-east Queensland. Pastures were grazed continuously at three set stocking rates : 1 beast to 1 1/2 acres, 1 beast per acre, and 2 beasts per acre. Grazing commenced 3 1/2 months after sowing and continued for two years. Mean liveweight production over the whole period at the medium stocking rate of one beast per acre was 0.92 lb a head a day. Production was closely related to stocking rate : gain per head decreased and production per acre increased as stocking rate increased. Nitrogen fertilizer increased animal production at the heaviest stocking rate. Seasonal pattern of animal production was influenced by stocking rate, but, in general, a winter--early spring period of small gains or losses of weight was followed by a rapid increase in late spring--early summer, with the rate of gain decreasing from mid-summer onwards. This followed the seasonal pattern of pasture production : little or no production over the cool dry winter, but high yields of forage during summer. No close relation was detected between liveweight gain and green forage available in the period of rapid increase in liveweight. During the phase of declining pasture and animal production, liveweight increment was related to available pasture expressed as green material minus S. almum stem. Crude protein content of unfertilized S. almum varied from 15 per cent for green material in spring to 2.5 per cent for the dry forage available in winter. Urea increased both yield and protein content.