bluuebunny/crossref_metadata_2025 huggingface dataset:
Some factors causing variation in the yield of individual plants of wheat
Authors: Knight R
Published: November 2004

Seeds of wheat (cv. Warimba) were sown by broadcasting to achieve a crop density of 160-180 plants m-2. The emergence date of each seedling was recorded. For each plant, measurements were made of the distance to neighbouring plants, and the weights and yields of these neighbours. Broadcasting the seed had ensured that there was variation in the distance to neighbours and also variation in the area postulated to be occupied by each plant. These areas varied in shape. Regression analysis was used to evaluate the effect of rapidity of emergence, the area available to a plant and the effect of competition from neighbours on the yield of each plant. Those plants that emerged 5 days after seeding on average had three times the yield of plants that emerged on day 12; however, there was very great variation around the regression, and emergence accounted for only 3.8 % of the variation in yield. Variation in the area available to a plant accounted for 14.3 % of the variation in yield and a competitive index made up of the size and distance away of neighbours accounted for 8.3 %. Each of these factors had a statistically significant effect on final yield. When they were combined in a multiple regression they accounted for only c. 20% of the variation, and 80% remains unexplained. Competition was shown to vary from plant to plant; it was not solely a communal effect reducing plants similarly. The shape of the area postulated as being available to a plant could not be shown to have an effect on its yield. The results are discussed in reference to measures of competition and the difficulties experienced by plant breeders when attempting to select among single plants for yield.
The effect of time of sowing on the grain yield of irrigated wheat in the Namoi Valley, New South Wales
Authors: McDonald GK , Sutton BG , Ellison FW
Published: November 2004

The effect of time of sowing on the yield of 15 wheat cultivars grown under irrigation was examined at Narrabri, N.S.W. Sowing dates, which ranged from mid-April to mid-August, encompassed the period of sowing normally found with commercial crops. The length of the pre-anthesis period was affected by both temperature and photoperiod. There was evidence of a vernalization requirement for some of the winter and midseason cultivars, but, overall, photoperiod was the more important environmental factor determining pre-anthesis development. Each day's delay in sowing caused a delay of between 0.48 and 0.75 days in anthesis; the delays observed for spring wheats were generally greater than those reported for dryland wheat in eastern Australia. Winter cultivars generally did not show an optimum sowing or anthesis date. For spring cultivars, the optimum time of sowing was early June (range of about 3 weeks), while the optimum anthesis date was the last week of September (range of 1 week). Grain yields of spring cultivars were reduced by 6 and 16% per week's delay in sowing and anthesis respectively. Despite a non-limiting water supply, yields at late plantings were low, which was largely the result of hastened crop development and high temperatures during grain-filling. The environmental factors which determined the optimum sowing and anthesis dates were the incidence of early spring frosts and high spring temperatures. If frosts were not a factor at Narrabri, the optimum time of flowering would be 6-8 weeks earlier than the present optimum.
The effects of nitrogen nutrition of plants on the development of acidity in Western Australian soils. II. Effects of differences in cation/anion balance between plant species grown under non-leaching conditions
Authors: Jarvis SC , Robson AD
Published: November 2004

The effects of supplying different forms of nitrogen on the cation/anion balance and associated changes in soil pH of four agricultural species (wheat, perennial ryegrass, subterranean clover and white clover) were examined. Plants were grown in unleached pots in an acidic, poorly buffered, sandy soil from Western Australia. Acidity was increased by over 1.0 pH unit when plants took up NH+4 and by up to 0.6 pH units when legumes were dependent upon symbiotically fixed N. In contrast to the previous studies with leached soil, acidity was decreased when plants took up NO-3. The relationship between the excess cation content (or ash alkalinity) and the final soil pH differed amongst the four species. Although lower ash alkalinity was always associated with higher acidity, much smaller changes in ash alkalinity in wheat and ryegrass were associated with bigger changes in pH than was the case with the legumes. The relationship between soil pH and ash alkalinity of subterranean clover shoots was markedly different from that for the other three species. Both extractable aluminium levels in the soil and manganese concentration in the plant shoots increased with decreasing ash alkalinity in the shoots through the effect on soil pH.
The productivity of breeding ewes grazing on lucerne or grass and clover pastures on the tablelands of southern Australia. II. Wool production and ewe weight.
Authors: Donnelly JR , Morley FHW , McKinney GT
Published: November 2004

Spring-lambing Merino and crossbred ewes grazing on dryland lucerne pastures were generally heavier throughout the year than ewes grazing on phalaris and subterranean clover pastures, even though they experienced greater weight losses during winter. These losses were mostly eliminated by compensatory gains in spring. Annual fleece weights of the Merino ewes grazing on lucerne or phalaris and subterranean clover pastures declined linearly by 146 and 64 g respectively for each additional ewe carried over a range of stocking rates from 9 to 18 ha-1. Corresponding figures for crossbred ewes were 114 and 46 g. In each case the difference between pasture species was significant (P < 0.02). Only at the lowest stocking rates were fleeces from ewes on lucerne heavier (by c. 500 g) than those from ewes on phalaris. At the highest stocking rates, there were no advantages in terms of wool production from grazing breeding ewes on lucerne. Not only was there a greater need for supplementary feed during late pregnancy to avoid losses from pregnancy toxaemia, but the lucerne pastures at all stocking rates proved more sensitive to unfavourable physical and chemical characteristics of soils than did phalaris and subterranean clover pastures. The fleece weights of Merino and crossbred ewes declined, on average, by 70 and 50 g per year for ewes aged between 1+ and 6+ years. Pregnancy reduced fleece weights by 5-10% in Merinos and 5-21% in crossbred ewes, depending on seasonal conditions which varied from year to year. For Merinos only, dry ewes grew about 4% more wool than lactating ewes. No other effects of reproduction on fleece weights were observed.
Field measurements of nitrogenase activity in soils amended with wheat straw
Authors: Roper MM
Published: November 2004

Nitrogenase activity and decomposition of straw were examined in situ in two areas (Gunnedah and Cowra) representative of large areas of the New South Wales wheat belt. Measurements of nitrogenase activity were made by adapting the acetylene reduction assay for use in the field. Evolution of CO2 was monitored as an indirect measure of decomposition of straw. The addition of straw to soil stimulated nitrogenase activity which was related to the amount of straw added and the rate of straw decomposition. There were significant levels of activity provided the soil was moist and warm. Nitrogenase activity increased with mean daily soil temperature (up to at least 30�C) and decreased as the soil dried from field capacity. It is concluded that nitrogen fixation by free-living nitrogen-fixing microorganisms in soils amended with straw may contribute to the nitrogen status of the soil and thus reduce the need for nitrogen fertilizers.
Responses of grain sorghum to varying irrigation frequency in the Ord irrigation area. II. Evapotranspiration, water use efficiency and root distribution of different cultivars
Authors: Myers RJK , Foale MA , Done AA
Published: November 2004

Four grain sorghum cultivars (Quicksilver, Texas 610SR, E57 and Q7844), representing early-to-late maturity types, were grown under different irrigation frequencies (7-day, 14-day, 28-day or 42-day intervals or once-only-at-sowing) in the dry season in the Ord Irrigation Area. Soil water distribution, root distribution and evapotranspiration were determined periodically. Frequent irrigation resulted in shallow root development and most water use was from the surface 40 cm of soil. Depth of water extraction increased with plant age and with less frequent irrigation. The depth of root penetration determined by direct measurement was similar to that inferred from soil water profiles. Water uptake per unit length of root was related to soil water content only in the 0-40 cm soil layers. Ea/Ep (actual evapotranspiration/pan evaporation) was classified into three stages according to the degree of soil drying after irrigation. During the first stage, immediately after irrigation, Ea/Ep was generally close to 0.75 irrespective of cultivar, leaf area index (LAI) or irrigation interval. During the second stage, linear functions adequately described Ea/Ep as a function of LA1 for LA1 less than 5. During the third stage, which commenced when total soil water to 1.8 m declined to 545 mm, poor relationships between Ea/Ep. Following an analysis of the soil water use data, it is believed that maximum yields of sorghum may be attainable with irrigation at sowing followed by three carefully timed irrigations.
Studies on competition for sulfur between subterranean clover and annual ryegrass. I. Effect of nitrogen and sulfur supply
Authors: Gilbert MA , Robson AD
Published: November 2004

The effects of nitrogen and sulfur supply on growth and competition between subterranean clover (Trifolium subterraneum cv. Trikkala) and ryegrass (Lohum rigidum cv. Wimmera) were examined in a glasshouse experiment over a period of 45 days and in a field experiment over one growing season by using the de Wit model. Sulfur supply had no effect on competition between the species. Yield and sulfur content of both species in mixtures were at least equal to those in monoculture, irrespective of nitrogen and sulfur supply. In swards which were severely deficient in nitrogen, subterranean clover was more responsive to increasing sulfur supply than was ryegrass, but this did not cause interspecific competition. Under field conditions during spring, there was some indication that ryegrass was the superior competitor in sulfur-deficient swards which had received nitrogen fertilizer. Nitrogen application reduced the percentage of subterranean clover in the sward at all levels of sulfur supply, because it had a much greater effect on yield of ryegrass relative to the yield of subterranean clover. Sulfur application increased the percentage of subterranean clover in the mixed swards at each level of nitrogen supply.
Water uptake in relation to pre-harvest sprouting damage in wheat: grain characteristics
Authors: King RW
Published: November 2004

Water uptake by mature (post-dormancy) wheat grain was studied for a group of 50 wheat varieties of mostly Australian origin and in lines near-isogenic for grain coat colour (red v. white) and for hard v. soft grain. Cultivars differed widely (up to two-fold) in grain water uptake. Apparently these differences related to physico-chemical aspects of water imbibition by the grain. However, neither grain coat colour, pericarp or testa thickness, grain hardness nor grain protein content was correlated with grain water uptake. The degree of seed coat cracking was minimal as grain was dissected by hand from the ears. Grain germination after 30 h exposure to moisture was significantly correlated with its water uptake after 2 h of imbibition (r = 0.61). These findings, when combined with other information from this laboratory on varietal differences in ear water uptake, usefully characterize in-ear sprouting. Of the varietal differences in sprouting, 18% can be accounted for by differences in ear and grain water uptake. Differences in grain dormancy were deliberately avoided in these studies, but were evaluated separately at harvest ripeness in this same experiment. On the basis of varietal differences in grain dormancy and water uptake some breeding options are highlighted.
The effect of some fleece characters on the skin wax layer and fleece rot development in Merino sheep following wetting
Authors: James PJ , Warren GH , Neville A
Published: November 2004

This paper describes changes occurring on the skin surface following wetting and during the development of fleece rot and examines the effect of some fleece characters on these changes. One day of wetting reduced the average thickness of the skin wax layer from 7.82 to 4.90 �m, but there was little change In the proportion of the skin surface covered by wax. When hyperaemia of the skin was first noted the proportion of the skin surface covered by wax had decreased from 97.8 to 47.5% and the average thickness of skin wax had decreased to 3.64 �m. Cholesterol content of the skin wax increased steadily from the first day of wetting as fleece rot developed, whereas lanosterol content increased only in the early stages of fleece rot. Suint content of the fleece, measured before wetting commenced, was positively correlated with fleece rot score at all times during wetting. Suint also showed significant correlations with moisture content of the proximal portion of the staple, percentage of the skin surface covered by wax and cholesterol and lanosterol content of the wax. No relationship was observed between fleece rot score and fleece wax content, wettability, staple formation, tip formation, crimp definition or initial thickness of the skin wax layer.
Prediction of components of steer carcasses using tritiated body water space, fat depth and fasted liveweight or carcass weight
Authors: Bird PR
Published: November 2004

Chemical and dissectable components of the carcasses of 23 Hereford steers were related to whole body tritiated water space (T), fat depth at the 12/13th rib (FD), age, and 24 h fasted liveweight (LW) or cold carcass weight (CW). Fifteen steers were taken at intervals from a grazing experiment and were 15-22 months of age and 189-461 kg LW at slaughter. Six younger and two older steers were also used to expand the range to 3-33 months and 90-517 kg. All steers were taken from pasture 3 h after sunrise and deprived of feed and water thereafter. After 4 h, tritiated water was given intramuscularly and 20 h later blood was collected and the animals were weighed and slaughtered. One side of the carcass was minced and analysed for water, ash, nitrogen and fat. The other side was dissected into bone and boneless fractions. For each component the best single predictor and combinations of predictors which contributed significantly in the stepwise regression analysis (P < 0.05) are given. The use of T with LW or CW appreciably improved the precision of estimation of water, dry matter and chemical fat in the carcass. FD with LW or CW also improved the estimation of water, dry matter, fat and nitrogen. The combination of T, FD and CW best predicted water and fat. T, FD and LW best predicted fat in the carcass component of the live animal. The residual standard deviation of this regression was 3.3 kg v. 3.6 kg for LW and T, 6.1 kg for LW and FD, or 8.0 kg for LW alone.
Effects of grain shape and size on milling yields in wheat. I. Theoretical analysis based on simple geometric models
Authors: Marshall DR , Ellison FW , Mares DJ
Published: November 2004

Simple geometric models of wheat grains have been analysed to determine the effects of changes In shape and size on volume per unit surface area and hence potential milling yield. These analyses suggest that substantial changes In grain volume would have a greater effect on milling yield than would changes in grain shape. The shape and size of kernels of current Australian cultivars differ markedly from the optimum required to maximize volume per unit surface area (1 e. a spherical gram) Available data on genetic variability for grain size indicates that it should be possible to increase the gram size of Australian wheats by 50-100% and improve potential milling yields by 2-3%. However, while considerable genetic variation for grain shape also exists, the evidence available suggests that selection for optimal shape is likely to result in a correlated reduction in seed size thereby offsetting any gains achieved by changing seed shape.
Effect of temperature on seed development in jojoba (Simmondsia chinensis (Link) Schneider). I. Dry matter changes
Authors: Wardlaw IF , Dunstone RL
Published: November 2004

Growth of the capsule and seed of jojoba were followed from pollination to maturity at eight temperature regimens ranging from 15/10 to 36/31�C (8/16 h; photoperiod 16 h). There was an initial lag before the onset of rapid (linear) seed development, during which the capsule expanded, and this lag varied from 106 days at 15/10�C to 7 days at 36/31�C. The wax concentration in the seed was low during the initial stages of development, but reached a maximum when the seeds were 70-75% of their final dry weight. The maximum rate of dry matter accumulation in the seed increased with temperature up to 33/28�C but, because of the longer growth period at low temperature, seed size at maturity was greatest at 18/13�C. The current work suggests that prolonged periods with temperatures above 36/31�C, or below 15/10�C would be harmful to the development of jojoba seed. The high optimum temperature for growth rate of the seed (33/28�C) and sensitivity to a temperature of 15/10�C, puts jojoba into the same group as many subtropical species. However, the lower optimum temperature for seed weight at maturity (18/13�C) is close to that observed for the temperate cereals.
Field changes in germination requirements: effect of natural rainfall on potential germination speed and light requirement of Stylosanthes humilis, Stylosanthes hamata and Digitaria ciliaris
Authors: McKeon GM
Published: November 2004

The effect of isolated rainfall events on germination speed and light requirement was studied for different seed populations of Stylosanthes humilis, Stylosanthes hamata and Digitaria ciliaris. Initial germination, measured as the proportion of seeds germinating within 12 or 18 h under optimal laboratory conditions, was an important determinant of field germination where surface soil moisture is available for only short durations (12-18 h). Seeds were placed on the soil surface prior to rainfall, usually in the late afternoon, were resampled the following day when dry, and then stored in the laboratory before standard germination tests. The seed populations were exposed to 20 different rainfall events. Compared with unexposed seeds the seeds of all species germinated faster after exposure to rainfall, even a few mm, provided the rainfall was insufficient to cause field germination, e.g. germination of S. humilis increased from 46 to 70% in 12 h. Field germination was common in S. humilis, but little field germination of S. hamata and D. ciliaris occurred because of their slow germination. Initial germination of resampled seed was correlated with duration of surface moisture, whether this was received over one or two rainfall cycles. Seeds of S. hamata and S. humilis with the greatest increases in initial germination had a shorter imbibition time. The light requirement for rapid germination of S. humilis was not changed by rainfall, but the light-requiring fraction of D. ciliaris was reduced by exposure to rainfall (the reduction was positively correlated with duration of surface moisture) and high temperature (>50�C).
Factors affecting diet selection by sheep. 3. Dry matter content and particle length of forage
Authors: Kenney PA , Black JL , Colebrook WF
Published: November 2004

The effects of dry matter content and particle length of forage on potential intake rate and preference by sheep were investigated using six animals held in metabolism cages. In experiment 1, freshly harvested kikuyu grass (Pennisetum clandestinum) in its vegetative state was mixed in different proportions with similar material that had been oven-dried to form 15 diets ranging in dry matter content from 15 to 94%. Intake rate of wet matter decreased from 60 to 14 g/min as dry matter content increased, whereas the intake rate of dry matter increased from 9 to 14 g/min as the dry matter content of forage rose to about 40% but remained relatively constant thereafter. In experiment 2, undried kikuyu grass was eaten faster and formed a greater proportion of total intake than did dried kikuyu when expressed on a wet matter basis, but the amount of dry matter consumed from each forage was similar when they were offered together in separate containers. Kikuyu chopped to 10-mm length was eaten faster and was also preferred over kikuyu cut to 40 mm, irrespective of its dry matter content. Factors other than intake rate such as taste, odour or feel did not contribute markedly to the preference for either undried or dried kikuyu. Equations developed previously using results from dried forages predicted preference from intake rate quite well for dried forage but not for undried forage. It is suggested that the intake rate of dried forages may be a useful predictor of the preference for dry matter with forages containing any proportion of moisture, but further research is needed.
Germination and seedling growth of prairie grass, tall fescue and Italian ryegrass at different temperatures
Authors: Hill MJ , Pearson CJ , Kirby AC
Published: November 2004

We measured the effects of temperature on the germination, emergence and growth during early tillering of Italian ryegrass (Lolium multiflorum), prairie grass (Bromus catharticus) and tall fescue (Festuca arundinacea). Radicle emergence (the percentage of seeds with emerged radicles) and 'field' emergence (the percentage of seeds with shoots > 1 cm long) were reduced at 35�C (constant, all lines), or 30/25�C (12/12 h, prairie grass and Tama Italian ryegrass only). All lines took longer to germinate at 15 and 10�C (constant) than at higher temperatures, and final percentage germination of tall fescue lines was lower at 10�C (constant) than at other temperatures. Italian ryegrass had the fastest shoot extension, and consequently the fastest 'field' emergence. Seed respiration rates were higher in fescue than in the other lines at 4 days from imbibition, and rates rose in all lines at 8 days. Over the first 20 days after sowing, growth rates were closely related (r = 0.87-0.99) to weights of seed and caryopses, when account was taken of perenniality (which was associated with relatively slow growth) and polyploidy (which was associated with growth faster than might be expected from seed size alone), and a multivariate relationship including temperature was developed (R2 = 0.88). Growth rates of shoots at 20 days after sowing were ranked Tama Italian ryegrass > prairie grass > Ucivex Italian ryegrass > tall fescue, and 24/19 > 21/16 > 18/13 > 30/25 > 15/10�C. Growth during tillering, up to 42 days after emergence, was ranked Italian ryegrass > prairie > tall fescue and 21/16 = 18/13 > 24/19 = 15/1O�C. Relative growth rates and relative rates of tillering were independent of temperature in Italian ryegrass, but were lower at 15/10 and 24/19 than at 21/16 and 18/13�C in prairie grass and tall fescue. Prairie grass had higher yield per tiller but lower tiller numbers than Italian ryegrass; tall fescue had both lower yield per tiller and lower tiller number. Italian ryegrass was therefore the species best adapted to variations in environment and competition at sowing.
The productivity of breeding ewes grazing on lucerne or grass and clover pastures on the tablelands of southern Australia. 4. Lamb growth
Authors: Donnelly JR , McKinney GT , Morley FHW
Published: November 2004

Lambs were weighed at 6 and 12 weeks of age in 2 years in an experiment at Canberra in which their dams were stocked at six rates from 9 to 18 ha-1 on pastures sown to subterranean clover and either lucerne or phalaris. The ewes, either Merino or crossbred, were joined with Merino and Border Leicester rams over 5-week periods and lambed in mid-August or early September. In a year with moderate rainfall, single lambs reared by ewes at the mean stocking rate (13.5 ha-1) on lucerne were c. 1 kg or 8% heavier at 6 weeks (P<0.01) than those on phalaris, and c. 2 kg or 20% heavier in a much drier year when feed was scarce in winter and early spring. This weight advantage of those on lucerne increased by c. 70 g day-1 between 6 and 12 weeks of age only in the drier year. Lambs born in early September were up to 2.7�0.39 kg heavier at 6 weeks than those born in mid- August (P < 0.01); this difference did not change between 6 and 12 weeks (P > 0.05). Lamb weights declined linearly with stocking rate, more so on lucerne than on phalaris pastures (P < 0.01); this was correlated with the effect of stocking rate on maternal weight at lambing. Sire effects were more important for lambs from Merino than from crossbred ewes. Maternal effects were larger for lambs sired by Merino than by Border Leicester rams at 6 weeks but less so for weight gains between 6 and 12 weeks.
The effect of the Triticum timopheevi nucleo-cytoplasmic system on the performance of an F1 hybrid wheat
Authors: Walcott JJ
Published: November 2004

Hybrid performance may be affected by the T. timopheevi nucleo-cytoplasmic system for producing hybrid wheat. Its effects were investigated in three experiments which compared the same hybrid genotype produced either in T. aestivum cytoplasm or in T. timopheevi cytoplasm. Few consistent differences were found between the two hybrids. The only significant difference in grain yield was associated with a significantly reduced seed set in the T. timopheevi hybrid, and suggested a likely effect of location on the degree of fertility restoration achieved. The T. timopheevi nucleo-cytoplasmic system appeared to reduce plant stand and test weight, but to improve flour colour and flour protein content relative to the T. aestivum hybrid.
Transformations and transfers of nitrogen after irrigating a cracking clay soil with a urea solution
Authors: Freney JR , Simpson JR , Denmead OT , Muirhead WA , Leuning R
Published: November 2004

The effectiveness of applying urea fertilizer (120 kg N ha-1) in irrigation water was investigated in a commercial sunflower crop on a calcareous, cracking clay soil. This method of fertilizer application resulted in fairly even distribution of applied nitrogen (N) within the soil profile down to the bottom of the plough layer and along the field in the direction of flow. At physiological maturity (76 days after fertilization) the data suggest that 57 kg of the applied N per hectare was recovered in the plant tops and the bulk of this (42 kg) was in the grain. Less than 2 kg N was lost as ammonia (NH,) and c. 2 kg N was emitted as nitrous oxide (N2O) during the first 23 days after fertilizer application, when most of the N not recovered by the sunflowers was lost. Slightly more than half of the N2O emitted was lost during the 11 days after fertilization, when NH+4 was being nitrified; the remainder was lost after a second irrigation by which time most of the urea had been converted to nitrate. A partial N balance suggests that within 20 h of the second irrigation a substantial amount of N (between 22 and 30 kg ha-1) was lost as a result of denitrification. Thus, although the method of application of fertilizer N is simple and cost effective, produces an even distribution of applied N across the field, and reduces NH3 loss, it still appears to be subject to substantial losses of N, presumably by denitrification, during subsequent irrigations.
A glasshouse screening procedure for identifying citrus hybrids which restrict chloride accumulation in shoot tissues
Authors: Sykes SR
Published: November 2004

Twelve-month-old citrus rootstock hybrids, from crosses made during springs 1980 and 1981, were screened for chloride accumulation in leaves following a short-term salt test under glasshouse conditions. Seedlings were grown in nutrient solution cultures containing 50 mM NaCl for 56 days. Individual hybrids were selected for further evaluation, mainly on the basis of low leaf chloride concentrations but also on visual symptoms of salt damage. The reliability and accuracy of the screening procedure for identifying new hybrids which restrict chloride accumulation in shoots were evaluated in four replicated glasshouse experiments. These were conducted with plants propagated from cuttings taken from selected hybrids. The first of these experiments compared four hybrids selected from two crosses, Rangpur lime x Trifoliate orange and Cleopatra mandarin x Carrizo citrange, with seedlings of parent cultivars. Plants were grown in coarse river sand irrigated with nutrient solution � NaCl (50 mM) over a 56-day period. Two Rangpur lime x Trifoliate orange hybrids and one Cleopatra mandarin x Carrizo citrange hybrid accumulated similar chloride concentrations in shoots as Rangpur lime and Cleopatra mandarin. The other three experiments were conducted using solution cultures as in the original screening experiments (i.e. 50 mM NaCl, 56 days). Within each experiment there was a significant positive correlation between mean leaf chloride concentration of replicated hybrids and those measured for each hybrid in original screening experiments. Although there were a few escapes, results demonstrated that the original screening experiments were for the most part reliable and accurate.
An analysis of the environmental limitation to yield of irrigated grain sorghum during the dry season in tropical Australia using a radiation, interception model
Authors: Muchow RC , Coates DB
Published: November 2004

Variation in yield of irrigated grain sorghum (Sorghum bicolor L. Moench) grown during the dry season in tropical Australia was analysed in terms of the amount of photosynthetically active radiation (PAR) intercepted, its efficiency of use in dry matter production and the proportion of dry matter partitioned to grain. Three commercial hybrids (Texas 610SR, Dekalb DK55, Pacific Monsoon) grown under favourable conditions on two soil types (Cununurra Clay and Ord Sandy Loam) yielded similarly, but there was a significant effect of sowing date. Grain yield was highest (9.5 t ha-1 at 14% moisture) in the May sowing, with the lowest yield (7.4 t ha-1) being obtained in the April sowing. Yield was intermediate from a July sowing. Differences in grain yield across the dry season were not related to the amount of PAR intercepted, nor to the efficiency of conversion of intercepted PAR into net aboveground dry matter, but rather to differences in dry matter partitioning. A stable efficiency of conversion of 2.4 g MJ-1 of intercepted PAR was recorded for the entire crop cycle for sorghum crops growing under favourable growing conditions in this environment. This conversion efficiency for a tropical C4 cereal is similar to maximum values, but higher than average conversion efficiencies over the entire crop cycle obtained for temperate C3 cereals growing in temperate regions. Temperature did not affect this conversion efficiency, but had a pronounced effect on the duration of crop development.
Effect of sowing date on growth and development of irrigated peanuts, Arachis hypogaea L. cv. Early Bunch, in a monsoonal tropical environment
Authors: Bell M
Published: November 2004

An experiment was conducted to study the effect of sowing date on the growth and development and commercial yield of Early Bunch peanuts under irrigation in the monsoonal tropical environment of the Ord River Irrigation Area. Sowing dates, which ranged from 7 December to 1 March, represented a wider range than that currently considered optimal for peanuts in this environment. Differences in above-ground dry matter production among sowing dates were primarily the result of differences in cumulative interception of incident light due to different leaf area duration. Later sowings showed progressively slower canopy development, with those in February and March intercepting only 75 and 60% of the cumulative light intercepted by those in December-January. Vegetative development was very responsive to sowing date, with progressive reductions in vegetative dry matter occurring as sowing was delayed between January and March. The proportion of vegetative dry matter as leaf and stem was also affected by sowing date, in that the leaf to stem ratio measured at approximately 75 days after emergence was greater for later sowings. This effect was associated with temperature and photoperiod during the period from emergence to day 75. Pod development was less affected by sowing date than vegetative yield, with accumulation rates and commercial pod yields being reduced by 28 and 31%, respectively, for the final sowing date (1 March). This was the result of a greater proportion of assimilate being partitioned to the reproductive components in later sowings. Pod numbers were more sensitive to sowing date than pod yield, but later sowings tended to compensate for lower pod numbers by having higher average pod weights. Later sowings also tended to have larger sound mature kernels, and this was associated with temperature and photoperiod during kernel development.
Simulated soil and plant management effects on root rots of subterranean clover
Authors: Smiley RW , Taylor PA , Clarke RG , Greenhalgh FC , Trutmann P
Published: November 2004

Pasture productivity in southern Australia is often limited by root diseases of complex etiology. The influences of simulated plant and soil management procedures on subterranean clover (Trifolium subterranean cv. Woogenellup) root rots were evaluated in controlled environments, using a soil from an irrigated and from a dryland pasture. Root rot incidence and severity were high in soils collected and used as intact cores, and low to moderate in soils disturbed while being collected. Simulated cultivation of soil in cores also reduced root rots in the dryland pasture soil that had little surface litter, but not in the irrigated pasture soil which had high levels of organic debris (and pathogen inocula) distributed through the surface 0-11 cm. Root rot was mild on plants in continually moist cores at 10�C, and severe in cyclically wetted and dried cores at 10, 15 and 20�C, and in continually moist cores at 15 and 20�C. Root rots were reduced by treatment of seeds with Rhizobium, fungicides, or both, by drenching soils with fungicides, and by planting the resistant T. yanninicum cvv. Larisa, Meteora and Trikkala. Removal of seedling leaves, to simulate grazing, accentuated root rot severity. The identified pathogens included species of Pythium, Fusarium, Rhizoctonia, and nematodes. Integrated strategies for controlling root rots of subterranean clover are considered promising in view of these studies with cores of pasture soils.
Effects of early season waterlogging on maize growth and yield
Authors: Mason WK , Pritchard KE , Small DR
Published: November 2004

Five irrigation treatments (0, 2, 6 and 24 h ponding in furrows plus a 6-h flooded treatment) were applied at the first two irrigations after emergence of a maize crop. Water was ponded for 6 h in the furrows or on the flooded plots at each of the 10 subsequent irrigations.The irrigation treatments had a significant effect on plant growth, resulting in final DM yields of 22.3, 19.7, 19.2, 18.7 and 13.9 t/ha for the 0, 2,6, 24 h furrow irrigations and the 6 h flood treatment respectively. The 2, 6 and 24 h furrow treatments did not perform differently in any of the parameters measured, indicating that a threshold level of waterlogging was reached in all three compared with the zero ponding treatment.Nitrogen applications of 25 kg N/ha to the soil or foliage prior to each of the first two irrigations did not reduce the severity of the waterlogging treatments, despite herbage N levels being significantly depressed in the flooded plots. Similarly, soil fungicide application did not mitigate the waterlogging effects.Individual plants within the treatment populations differed greatly in their response to the waterlogging treatments. The effect on individual plants persisted until final harvest. Cultural methods which may prevent the yield losses associated with the first irrigation of maize are discussed.
Viruses infecting hop, Humulus lupulus, in Australia
Authors: Munro D
Published: November 2004

In 1981 a survey of the main commercial hop cultivar in Australia, Pride of Ringwood, showed that foliar symptoms were associated with the presence of carlavirus particles. The incidence of plants containing particles varied between fields from 0 to 58%. In 1982 a survey based on enzyme-linked immunosorbent assay showed that the carlaviruses were hop mosaic and hop latent viruses and that they infected 1-68% and 1-58% of plants respectively. Prunus necrotic ringspot virus infected 4-9% of plants. Arabis mosaic virus was detected in a cultivar of English origin and American hop latent virus in cultivars of recent American origin, but neither of these viruses was detected in Australian-bred hops. Virus-free plants suitable for propagation were located in cultivars Pride of Ringwood and B23, and were produced by heat treatment and meristem culture of cultivar Southern Cross.
Effects of time of urea application on combine-sown Calrose rice in south-east Australia. III. Fertiliser nitrogen recovery, efficiency of fertilisation and soil nitrogen supply
Authors: Humphreys E , Chalk PM , Muirhead WA , Melhuish FM , White RJG
Published: November 2004

A combine-sown crop of Calrose rice was grown on an alkaline self-mulching grey clay soil. Prilled urea (50 kg N ha-1) was broadcast at four different times: sowing, before permanent flood, after permanent flood and panicle initiation. Field microplots received 5 atom % 15N-labelled urea at the same times. Plant recovery of 15N applied at sowing was only 3.8%, with 80% unaccounted for. The data are consistent with the poor performance of rice fertilised at sowing (Part I) and the disappearance of mineral N from the top 20 cm of soil during the flushing period (Part II). Plant recovery of 15N applied after permanent flood was also relatively low (28%) with a loss of 45%. Even where fertiliser was used most efficiently in producing more grain (application before permanent flood and at panicle initiation), substantial losses were incurred (25-40%), with plant recoveries up to 41%. The lack of significant amounts of excess 15N in the soil at depths below 10 cm was consistent with the suggestion that leaching was not an important loss mechanism and that losses may be reduced by deep placement of the fertiliser (Part II). The majority of the nitrogen in the plant tops was derived from soil nitrogen, even where fertiliser nitrogen was used most efficiently, thus emphasising the importance of the rate and pattern of release of the soil N supply. Fertilisation increased soil nitrogen uptake by up to 7 kg N ha-1.
Studies on the growth and carcass composition in Daldale wether lambs. 2. The effect of dietary protein/energy ratio
Authors: Soeparn o , Davies HL
Published: November 2004

Two experiments on the effect of dietary protein/energy ration on growth and carcass composition in Daldale wether lambs were carried out.In experiment 1, two groups of eight lambs in each group were fed in pens at a restricted intake (30 g air-dry feed per kg liveweight) either on a high protein/high energy diet (HP/HER) (20.7% crude protein) or on a low protein/high energy diet (LP/HER) (10.3% crude protein). The lambs were grown from 24.8 kg liveweight until slaughter at 37.5 kg. In experiment 2, two groups of eight lambs in each group were fed in pens a pelleted diet ad libitum, either on a high protein/high energy ration (HP/HEA) or on a low protein/high energy ratio (LP/HEA). The lambs were grown from 22.0 � 0.8 kg liveweight until slaughter at 37.5 kg. Those lambs on the HP/HE diets grew significantly faster than their counterparts on the LP/HE diets. Accordingly, animals given the HP/HE diets showed a superior feed conversion ratio than animals given the LP/HE diets. Despite these differences, there was no overall differences between treatments either at restricted or at ad libitum intake in the weight of carcass, the dressing percentage, and in the chemical composition of the carcass. In general, the carcasses produced contained a similar amount of fat (30.6%-32.9% of carcass). It was concluded that varying protein to energy ratio in diets affected liveweight gain and feed conversion ratio, but did not affect carcass composition.An experiment was conducted on the diets to investigate some aspects of digestion in the stomach and intestines at the two levels of crude protein.Dietary crude protein level had little effect upon the apparent digestibility of organic matter (OM) and neutral detergent fibre in the whole tract, the proportion of NDF digested in the stomach, the total volatile fatty acid concentration (VFA) in the rumen and the proportions of individual VFA.The flow of rates of digesta from the rumen and abomasum were also similar for the two diets. However, the proportion of the total digestion of OM occurring in the stomach decreased, while the flow of total N and crude protein (CP) (total N minus ammonia N x 6.25) to the intestines and the amounts of N and CP digested therein was higher on the HP diet.The data from the digestion experiment showed that the amount of digestible CP in the intestines per unit of digestible OM intake did not affect carcass composition.
Variation in leaf area development and its effect on water use, yield and harvest index of droughted wheat
Authors: Richards RA , Townley-Smith TF
Published: November 2004

Genotypes, chosen because of their variation in flowering, tillering and early leaf growth, were evaluated in 1 m long tubes in a glasshouse. These traits were selected for two reasons: firstly, because it was presumed they influence leaf area development and hence the water use, harvest index and yield of droughted wheat; secondly, because they are amenable to genetic manipulation and therefore can be selected in a breeding program. Four drought treatments were imposed in each of two seasons. The treatments and cultural conditions simulated droughts encountered by field-grown crops. Grain yield varied according to the amount of growth and water use before and after anthesis in relation to soil water supply. In the wettest treatments where plants had adequate water up to anthesis but were droughted thereafter (akin to a wet mediterranean-type environment), grain yield was positively associated with the amount of preanthesis growth. In the drier treatments, where droughts were sustained from before anthesis, genotypes having traits that reduced leaf area index saved more water for use after anthesis and had a higher harvest index and grain yield. However, pre-anthesis growth was also important, as it was estimated that in the driest treatments up to 60% of the grain dry weight was formed from reserves present at anthesis. These reserves represented up to 15% of the above-ground biomass at anthesis. Harvest index (y) was a nonlinear function of the proportion of water used after anthesis (x), y = 0.10 + 0.13 ln(x), r2 = 0.82 (P < 0.01).The determinate tillering or 'uniculm' wheats, although having some advantages over conventional tillering lines when sown at the same density, were largely indistinguishable from conventional wheats in their water use pattern when sown at twice the density. However, at both densities they had a higher stem weight per unit length and a higher specific leaf weight than conventional wheats, and this resulted in them having a lower harvest index and grain yield. These pleiotropic effects may reduce the possible advantages of these wheats, that is a reduced maximum leaf area and no sterile tillers, in dry environments.
Susceptibility of Australian wheats to Pyrenophora tritici-repentis
Authors: Rees RG , Platz GJ , Mayer RJ
Published: November 2004

The response of Australian wheats to yellow spot caused by Pyrenophora tritici-repentis has been examined under controlled conditions with a juvenile-plant screening system. About three-quarters of contemporary Australian wheats are highly susceptible to the disease and very few cultivars possess useful levels of resistance. Also, the majority of Australian wheats now undergoing final evaluation before releasing are highly susceptible to yellow spot. Modern wheats grown in Queensland and northern New South Wales are, as a group, more susceptible than those they replaced, and this may have contributed to the upsurge in yellow spot in the region. In two comparisons between ratings on juvenile plants under controlled conditions with field disease assessments and yield measures, the juvenile plant ratings and field disease assessments explained similar proportions of the variation in yield measures.
Prospects for the biological control of silver-leaf nightshade, Solanum elaeagnifolium, in Australia
Authors: Wapshere AH
Published: November 2004

A survey of the distribution of the herbivores associated with the weed, Solanum elaeagnifolium, in its native range in Mexico and south-west U.S.A., has been made in relation to climate. The biological control agents considered were: a leaf-galling nematode, Orrina phyllobia; the defoliating cassidine Gratiana pallidula; chrysomelids Leptinotarsa texana and L. defecta, and tingids, Gargaphia spp.; a stem-boring curculionid, Trichobaris texana; a stem-galling cecidomyid species; the fruit-feeding gelechiid, Frumenta nephelomicta; and tephritid Zonosemata vittigera. The results of the survey suggest that the herbivores would not be sufficiently climatically adapted to the summer-drought, cereal-growing areas of southern Australia most heavily infested by the weed, to control it there. They might establish and be useful in areas less heavily infested by the weed in summer rainfall climates and in irrigated crops.
Factors limiting the intake of feed by sheep. 10. The effects of concentrate supplements on the voluntary consumption and digestion of a medium quality roughage
Authors: Weston RH
Published: November 2004

Feed intake and digestion studies were conducted with sheep offered a medium quality roughage and given various concentrate supplements. The provision of supplements in amounts equal to c. 23% of voluntary roughage consumption always decreased roughage intake. The decrease with wheat-based supplements was little affected by supplement feeding frequency, by use of ground grain rather than whole grain or by the provision of additional essential nutrients, but its magnitude was reduced by c. 30% with use of buffer salts to prevent decline in rumen digesta pH. The supplements were associated with less digesta in the alimentary tract and less rumination. Supplements increased the rate of liquor outflow from the reticulum and the rate of marker clearance from the reticula-rumen. The rumen digesta and reticulum digesta differed with respect to particle size distribution and only some 30% of the organic matter in reticulum digesta was in particles too large to pass to the omasum. The data were considered to be consistent with a concept that the regulation of roughage intake involves an interplay between the animal's energy metabolism and the quantity of digesta in the reticula-rumen and to indicate (i) some discrimination against the larger particles in digesta flow from the rumen to the reticulum, (ii) appreciable discrimination on the basis of size of particle in digesta flow from the reticulum to the omasum, and (iii) regardless of state of subdivision, constraints applied to digesta passage to the omasum which could have affected the level of feed intake achieved.