Search

High rates of fertiliser applied to boost pasture growth in the southern Australian sheep industry may lead to eutrophication of waterways and groundwater degradation. A field study was used to investigate whether higher fertiliser and stocking rates would increase nutrient loss in runoff and subsurface flow from pastures. Phosphorus (P) and nitrogen (N) concentrations in surface and subsurface flow were measured from 1998-2000 in four 0.5-ha hillslope plots. Surface flow volume was measured directly and subsurface water flux was estimated using soil moisture data and a water balance model. A simulated rainfall study was also conducted using 0.64-[m.sup.2] plots. The treatments represented were: a low-P set-stocked sown pasture (SS low P), a high-P set-stocked sown pasture (SS high P), a high-P sown pasture in a 4-paddock rotation (RG 4-pdk), and an unsown set-stocked pasture (Low P volunteer). No runoff from the hillslope occurred in 1999, while the volume of runoff in 1998 and 2000 varied from 0.1 to 68 mm/year across the 4 hillslope plots. More P was lost via surface runoff (up to 0.25 kg P/ha.year) than subsurface flow (up to 0.027 kg P/ha.year). However, N loads were greater in subsurface flows (3.2-10.6 kg N/ha.year) than surface runoff (0.04-2.74 kgN/ha.year). Phosphorus concentrations were higher in runoff from the high P treatments (0.34-0.83 mg P/L) than the set-stocked low P treatment (0.19-0.22mg P/L). Higher TP concentrations in runoff from the high P treatments were associated with greater labile P contents in the soil, dung, and herbage. However, the volume of runoff, rather than the pasture treatment, was the primary determinant of nutrient loss. Avoiding high nutrient inputs in seasonally waterlogged areas, sowing perennial pastures, and minimising stock camping helps minimise P losses to waterways and N losses to groundwater. Additional keywords: fertiliser, water quality, nutrient loads, soil fertility, hillslope hydrology., Introduction The high rainfall zone (>600mm) of southern Australia is dominated by dryland pasture, and since the mid 1990s, many sheep producers have increased fertiliser inputs and stocking rates to [...]

Control over the quantity and quality of food ingested by grazing ruminants in temperate pasture systems remains elusive. This is due in part to the foraging choices that animals make when grazing from communities of mixed plant species. Grazing behavior and intake interact strongly with the feed supply--demand balance, pasture composition, and grazing method. These interactions are not completely understood, even for relatively simple pasture communities such as a perennial ryegrass (Lolium perenne L.)--white clover (Trifolium repens L.) mixture. When offered a free choice between these species, ruminants exhibit a partial preference for clover compared to grass (about 0.7:0.3) and have a higher intake rate from clover but do not graze to maximize their dally intake of dry matter (DM). When monocultures of grass and clover are offered as a free choice in 50:50 area ratio, animal performance is no different than from a dover mono-culture alone. Thus, all of the feeding value benefits of dover are available when only 0.5 of the grazing area is sown to dover. These observations accord with the satiety theory and imply that there are constraints to eating pure dover that animals can overcome by adding grass to their diet, provided their ability to locate and ingest each food is not seriously limited. The challenge for grassland management is to present feed to animals at pasture in ways that allow them to meet their dietary preferences, while also allowing high rates of animal production per hectare.

White clover (Trifolium repens L.) herbage production in intensively grazed pasture is related to clover stolon growing point density. High stolon density is associated with small leaf size. The objective of this study was to examine the probability of breaking the genetically controlled link between leaf size and stolon density by manipulating internode length and branching propensity. Two white clover cultivars, Grasslands Tahora and Grasslands Kopu, were grown in two New Zealand environments, full sunlight or 50% sunlight (shade), during 1991 and 1992. Selections were made for high or low frequency of stolon branching, long or short stolon internodes, and large or small leaves. These selections were polycrossed within groups to give 24 lines. Lines were evaluated in pots grown outside to determine the effect of selection on these and other shoot characters. Selection of populations with high or low frequency of branching gave progeny with different frequency of branching for all cultivar-environment combinations except for selection within Tahora grown in shade. Selection of populations with long or short internode length gave progeny with different internode length in all cultivar-environment combinations. Selection for large and small leaflet width gave progeny with different leaflet width in all cultivar-environment combinations except for selection within Kopu grown in sun. Two estimates were made of narrow sense heritabilities. Estimates from mid-parent versus progeny regression heritabilities were higher for internode length and leaflet width than for frequency of branching. Realized heritabilities were again generally higher for internode length and leaflet width than for frequency of branching although there were some exceptions. Selection for high frequency of branching in Tahora grown in full sunlight had a high realized heritability. Stolon characters, such as internode length and frequency of branching, can be effectively manipulated by selection. The degree of selection success can be affected by environment and cultivar. Selection for variation in internode length is likely to be more successful than for frequency of branching.

The effects of sward surface height (SSH) and daily herbage allowance (HA) on the defoliation pattern and grazing mechanics of early lactation dairy cows grazing on irrigated perennial ryegrass–white clover pasture were studied. The hypothesis tested was that SSH and HA affect intake and diet selection through their effects on the pattern of defoliation which is influenced by the resistance to prehension bites. Factorial combinations of two initial SSH (14 and 28 cm) and two daily HA (35 and 70 kg DM cow−1 d−1) were examined in a replicated experiment. The peak longitudinal tensile force required to break the sward portion encompassed in a 100 cm2 area [bite fracture force (BFF100)] was measured as an index of the resistance to prehension. The volume of herbage defoliated and herbage intake increased with SSH ( P < 0·05) and HA ( P < 0·01). Corresponding to an increase in HA from 35 to 70 kg DM cow−1 d−1, there was a proportional increase in the total defoliation area (TDA) and intake by 0·24 and 0·55 in the short sward compared with 0·16 and 0·32 in the tall sward respectively. The results of this experiment suggest that a consistent spatial pattern of reduction of the canopy exists during defoliation by cows and that the volume of sward canopy defoliated is the major variable affecting herbage intake. The BFF increased down the sward profile at a rate that was higher ( P < 0·05) for the taller sward than for the shorter sward. It is proposed that a relatively lower resistance to prehension in the short sward compared with the tall sward explains the greater proportionate increase in TDA and intake corresponding to an increase in HA. The rate at which BFF100 increases down the sward profile is suggested as a sward physical variable that can influence the defoliation process. The estimated time and energy costs of prehension bites are discussed in the context that larger bites are handled more efficiently than smaller bites. [ABSTRACT FROM AUTHOR]

(1) The appearance and survival of Trifolium repens seedlings from naturally deposited seed were monitored for 3 years under different sheep grazing managements and phosphate fertilizer inputs, and in four slope aspect zones, in summer moist New Zealand hill country. (2) A mean of 5.5 seedlings m-2 per year appeared, representing 4.2% of the seeds deposited each summer. (3) Only 4.4% of seedlings survived to form established, stolon-bearing plants. representing a mean recruitment rate of one seedling per 5.5 m² per year. Survival was highest on steep north-west sites (10%), and nil on flat south-west sites, reflecting likely competitive stresses from surrounding vegetation. (4) Such low recruitment rates clearly indicate seedling regeneration plays only a minor role in T, repens persistence in this environment. Vegetative stolon densities of 3000 4000 m-2 and high rates of stolon initiation and death confirm that the species behaves essentially as a true perennial, (5) A useful ecological role for low seedling recruitment rates in maintaining genetic diversity within the T. repens population must be recognized, however, especially in highly variable environments. [ABSTRACT FROM AUTHOR]

(1) The appearance and fate (removal by livestock versus natural ripening and eventual seed deposition) of Trifolium repens flowerheads were measured for 3 years under different sheep grazing managements and soil fertility levels in a range of topographical (slope aspect) zones in summer-moist New Zealand hill country. (2) The spatial distribution of T. repens at the individual plant level (in 100 cm² quadrats) and thc treatment level were measured and related to flowerhead production. (3) Variation in flowerhead production between fertilizer levels largely paralleled variation in T. repens content of the sward, but there was a strong trend for greater flowering activity per unit of T. repens under rotational grazing than under set stocking. At the individual plant level, variation in density of T. repens foliage explained only 5 10% of the variation in numbers of flowerheads. Flowering appeared to be strongly influenced by micro-environment and genotype. (4) Removal of flowerheads, mostly unripe, by grazing stock was relatively consistent at 89-97% of flowerheads produced. On average, flowerheads were removed within 12 days of their appearance, with small treatment differences unlikely to influence thc viability of seed in consumed flowerheads. (5) Estimated seed yields were 275, 96 and 145 seeds m-2 (1.4, 0.5 and 0.8 kg ha-1) for the 3 years. 75% of which were hard seeds, Annual seed input depended much more on the number of flowerheads produced and the proportion of flowerheads grazed than on variation in yield per flowerhead. (6) Half-lives of buried seeds were estimated at about 1 year or less, with only 13% of seeds still surviving after 18 months in a simulated seed return experiment. High turnover rates in the buried seed pool indicate that seed reserves are likely to be relatively recent in origin and an ineffective source of new plants within existing swards. [ABSTRACT FROM AUTHOR]

A number of devices are available which can be incorporated at the electrical distribution board in a building to reduce the voltage and hence the power consumed by an existing fluorescent lighting installation. Certain of these are generally known as 'energy limiters'. Voltage reductions not only reduce power consumption but also cause a drop in light output and changes to other lamp operating conditions, depending on lamp type, ballast circuit and luminaire. This paper describes a detailed investigation of five voltage (RMS) reducing devices: four based on auto-transformers and one on a reverse phase electronic dimmer. Nineteen lamp and ballast circuit combinations and a range of luminaire types were studied. Data are given on the effects of voltage reduction on lamp light output, power consumption, lamp starting and stability, power factor, induced harmonic distortion and system efficiency. Potential problems are highlighted and economic factors are discussed. It is recommended that these devices are only considered for retrofit in areas where a decrease in illuminance is acceptable. A new lighting installation should be designed to operate at full rated supply voltage using modern energy-efficient lamps and luminaires to obtain the most effective lighting solution. [ABSTRACT FROM PUBLISHER]