Showing papers in "Crop & Pasture Science in 1987"

Decline of Vesicular-Arbuscular Mycorrhizae in Long Fallow Disorder of Field Crops and its Expression in Phosphorus Deficiency of Sunflower

Abstract: Poor growth of crops after long fallows (> 12 months) in cracking clay soils of the northern areas of the Australian grain belt is known as 'long fallow disorder'. Various crop species, including wheat (Tr~ticum aestivum L.), chickpea (Cicer arietinum L.), grain sorghum [Sorghum bicolor (L.) Moench], sudan grass [Sorghum sudanense (Piper) Stapf], sunflower (Helianthus annuus L.), soybean [Glyczne max (L.) Merr.] and maize (Zea mays L.), had less root colonization with vesicular-arbuscular mycorrhizal (VAM) fungi and plant weight after long fallows than after short fallows. An experiment was conducted with a phosphorus-deficient soil that had been either fallowed for 3 years or sequentially cropped to cotton, sorghum and sunflower. Cropped soil had more mycorrhizal propagules consisting of intzct spores and colonized roots than long fallow soil. In the glasshouse, mycorrhizal colonization of sunflower (cv. Hysun 33) developed quickly in previously cropped soil to peak at 80% of root length at 72 days (flowering), but in long fallow soil it proceeded slowly, attaining 35% of root length at 72 days. Inoculation of long fallow soil with 20% w/w cropped soil resulted in extensive root colonization (89% at 72 days), eliminated P deficiency symptoms and more than doubled plant growth and final P uptake. Inoculation with similar soil treated with gamma radiation to kill propagules of mycorrhizal fungi had no effect on plant growth. Sunflower grew extremely poorly in irradiated soil with considerable leaf necrosis due to P deficiency. Reinoculation with cropped soil resulted In high levels of mycorrhizal colonization and good plant growth. It was concluded that long fallow disorder is caused by a decline in viable propagules of mycorrhizal fungi during fallowing, resulting in poor root colonization and symbiotic effectiveness of a subsequent crop. Fertilizing with phosphorus (50 mg P/kg soil) delayed the development of mycorrhizal colonization, but increased final lengths of colonized roots at 72 days. Zinc fertilizer (15 mg Zn/kg soil) slightly improved mycorrhizal colonization, and basal fertilizer (N, K, S, Ca) substantially improved colonization in long fallow soil inoculated with cropped soil. Additional keyword: Vertisols.

Root length density and water uptake in cereals and grain legumes: how well are they correlated

Abstract: Total root length per unit ground area (La) is often considered to be directly related to the amount and rate of water uptake. Experiments were conducted to compare the water use of spring wheat, barley, lupin (L. angustifolius) and field pea on four differing soil types in drought-stressed conditions. The La values of cereals were consistently five to ten times as large as those of grain legumes, whereas the aboveground biomass was sim~iar and never greater than twice that of the grain legumes. Growing-season water loss (WL) from the soil profile was very similar for wheat and lupins, despite this big difference in root length. Soil evaporation may have been greater under lupins, but when crop water uptake was compared for the period when leaf area was greatest, rates of change in soil water content within the root zone were still similar and were not well correlated with La. Specific root water uptake (Ur) was consistently greater for lupin than wheat. Maximum rooting depth was better correlated with WL than was La in all cases. Higher Ur values in lupin and pea may be related to their large and abundant metaxylem vessels, which give much lower axial resistance than in cereals. These results provide strong evidence for genotypic variation in root morphology, density and root extension between dicotyledenous and monocotyledenous species. They also indicate that La is not necessarily the root morphological characteristic most responsible for efficiency of water uptake in drought-stressed environments.

Assessment of drought resistance in pearl millet ( Pennisetum americanum (L.) Leeke). II. Estimation of genotype response to stress

Abstract: The finding that the more than 50% of the variation in grain yield of pearl millet breeding lines in two different drought stress treatments could be attributed to variation in yield potential and time of flowering was used to develop a drought-response index (DRI) based on the residual variation in grain yield, adjusted for experimental error. DRI was positively correlated to measured yield in the drought treatments, and independent of both yield potential and time to flowering. DRI in both midseason and terminal stress treatments was unrelated to yield component structure in the irrigated control treatment, indicating that selection for plant type under non-stressed conditions will not influence drought response. DRI was correlated to both grain number per panicle, and grain yield per panicle in both stress treatments, suggesting differential ability to maintain normal grain number, and/or that grain yield per panicle was an important factor in response to stress. Maintenance of panicle number did not seem to be important for maintenance of yield under drought stress. The correlation of DRI and individual panicle yield was of sufficient magnitude for the latter to serve as a selection index in terminal stress. The use of a DRI as a component of breeding for better adaptation to stress is discussed.

The digestion of wheat starch in broiler chickens

Abstract: Apparent metabolizable energy (AME) of wheat for 6-week-old male broiler chickens was highly correlated with starch digestibility when pelleted diets containing 820 g wheat per kg were fed. Starch isolated from low-AME wheats was hydrolysed in vitro by chicken pancreatic amylase as rapidly as starch from high-AME wheats. When included in semi-purified diets the isolated starches were completely digestible. Digestibility of starch was poor and highly variable when 3-week-old chickens were fed unpelleted wheat diets, but improved with age. Oat hulls improved the digestibility of starch in young chickens fed unpelleted diets.

Assessment of Drought Resistance in Pearl Millet (Pennisetum americanum (L.) Leeke). I Factors Affecting Yields under Stress

Abstract: Yield trials of advanced lines of pearl millet were grown under midseason (panicle initiation to flowering) and terminal (flowering to maturity) drought stresses in the dry seasons of 1981, 1982, and 1983. Grain yield and its components were severely reduced by the terminal stress, but were little affected by the midseason drought, as there was compensation by later tillers for yield lost on the earlier shoots. The major factor determining grain yield of a genotype in both stress treatments was its time to flowering. Because of this, yield-yield component relationships under stress were a result of yield component-phenology relationships. Yield potential (measured in an irrigated treatment in the same field) was generally positively related to yield under stress, but accounted for a much smaller fraction of yield variation than time to flowering. These two factors together accounted for more than 50% of the total variation in grain yield under stress, suggesting that genotype drought response (drought resistance/susceptibility) was a secondary rather than a primary factor in differences in yield under stress among the genotypes tested.

Variation in leaf area development and its effect on water use, yield and harvest index of droughted wheat

Abstract: 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.

Effect of rotation and conservation tillage on earthworms in a red-brown earth under wheat

Abstract: The effects of two rotation and two tillage systems on earthworm populations have been studied in a red-brown earth under wheat. At the time of sampling, the earthworm population under direct drill was nearly double that under conventional cultivation. The total number of worms was not affected by crop rotation with pasture or lupins, but following pasture there were significantly more large worms. It is suggested that at this site the earthworm population may be responding rapidly to alterations in food supply and water stress under the different agricultural systems.

Population dynamics of Rhizobium japonicum strains used to inoculate three successive crops of soybean

Abstract: Three closely related strains of Rhizobium japonicum, equally effective in N2 fixation, were used to inoculate each of three successive crops of soybeans [Glycine rnax (L.) Merr. cv. Bragg] grown on the same block of land. The soil was a vertisol previously free of R. japonicum, and inoculant was applied at different rates by spraying a suspension of peat culture into the seed bed at time of sowing the seed. The populations of rhizobia that developed in rhizosphere and soil were counted at intervals during crop growth and in the fallow period between crops. There was usually a substantial decline in recovery of inoculant strains immediately after sowing. In soil initially devoid of R. japonicum, populations in the rhizospheres of young seedlings were related to rates of inoculation, but differences disappeared as the plants aged. Shortly after harvest, the soil contained large populations of rhizobia which increased up to 200 times during the fallow period between crops, probably due to release of bacteria from disintegrating nodules. The size of these populations was maintained up to the time of sowing the following crop. Although strains used for second- and third-year crops were dominated by already established rhizobia in rhizosphere colonization and nodule formation, the magnitude of the domination could be reduced by increased rates of inoculation. In soil already containing R. japonicum, the proportion of nodules formed by inoculant strains was greater than the relative number of inoculant rhizobia in the soil or the rhizosphere; this was ascribed to an advantage of specific placement of the inocula in that zone of the soil where infection foci first formed. The results are explicable in numerical terms and are discussed in relation to an inoculation strategy for maximum nodulation by applied inoculant in competition with rhizobia already established in soil.

Improvement of raw potato starch digestion in chickens by feeding oat hulls and other fibrous feedstuffs

Abstract: Ground oat hulls significantly improved the digestion of raw potato starch for male broiler chickens. The improvement was dependent upon the level of oat hulls in the diet and the size of the oat hull particles. Rice hulls and barley hulls were as effective as oat hulls in improving raw potato starch digestion when fibre particles were larger than 1 mm in length. Wheat bran and hemicelluloses isolated from oat hulls had no effect on starch digestion. The improvement in raw potato starch digestion was accompanied by an accumulation of fibre in the gizzard and muscular hypertrophy of this organ. Broken raw potato starch granules were also observed in the gizzard contents.

Cyclical Fleece Growth in Cashmere Goats

Abstract: Seasonal changes in fleece parameters were studied in mature feral doe goats, known to produce commercial quantities of cashmere and housed in natural light (NL) or continuous light (CL).Circannual changes in volume growth rate (VGR) of cashmere in NL were asynchronous with those of hair, resulting in maxima in April and November respectively, indicating that follicle-specific mechanisms are controlling the rate of follicle activities.Cycles of cumulative length of cashmere and hair in NL were synchronous. Cashmere maxima of 64.0 and 62.3 mm occurred in June and July respectively for two consecutive years. Distinct circannual cycles of linear growth (period, 365 days) were evident. While exposure to CL initially reduced the cycle period, after 2 years an extended cycle period emerged; this may have been due to photodesensitization.In NL, cashmere fibre diameter minima occurred at June-July and February each year. Hair fibres underwent only one cycle of diameter change each year. The period of the cycles was reduced by CL.An annual cycle of cashmere brush end fibre formation was apparent in NL. This cycle was associated with the cessation of growth in June-July, and a subsidiary event occurred between December and March. Continuous light accelerated brush end formation.Cyclic fibre shedding produced a circannual rhythm in fleece composition with maximum cashmere: hair ratio (CHR) in April-May in non-breeding goats. The maximum CHR of 5.9: 1 in NL did not reach its potential, as illustrated by the follicle S:P ratio of 6.9:1 in the skin. This suggests an irreversible loss of cashmere fibres from the fleece following the cycle of brush end formation in February.The maximum mean length of cashmere and time of occurrence were similar in grazing and penned does, although grazing does were only sampled in 4 months of one year.

Prediction of wheat yield loss due to competition by wild oats (Avena spp.)

Abstract: Field experiments were conducted to determine the effect of varying the density of wheat (cv. Gamut) and wild oats (Avena fatua and A. sterilis ssp. ludoviciana) on the grain yield of wheat. Wheat grain yields were reduced by wild oats through the reduction in number of tillers, and this competitive effect could be reduced by increasing the density of wheat. Increasing wheat plant density beyond the weed-free optimum was found to be unsatisfactory for wild oat control. The best model to describe the data comprised a parabolic wheat yield-density component and a hyperbolic yield loss component. Parameters in the yield-density component were calibrated using 36 data sets to account for variation in sowing date and available soil water. The parabolic model best described the effect of limiting soil water on the wheat yield-density relationship. The yield loss component, which included weed and crop density as variables, indicated that wheat and wild oats behaved as near-equal competitors.The predictive ability of the yield loss model varied when tested on several independent data sets collected from commercial wheat crops. This variation was caused by changes in the relative competitive ability of the crop and weed which resulted in significant variation in values of the yield loss parameters. Further refinement and generalization of the model will be possible if the yield loss parameters can be related to genetic and environmental variables.

Yield components and nitrogen partitioning of maize in response to nitrogen before and after anthesis

Abstract: Zea mays hybrid XL66 was grown with irrigation in sand in the field and subjected to different rates of nitrogen supply from floral initiation to anthesis and again from anthesis to maturity. Nitrogen supply during spikelet differentiation affected grain number markedly. Nitrogen supply during grain filling had a small but significant effect on the rate of grain filling and an effect on the rate of nitrogen entry to the grain, causing a 1.3-fold change in percentage grain nitrogen. Increasing the nitrogen supply produced larger plants, but the distribution of nitrogen and dry weight among plant parts were similar and the harvest indices for dry weight (0.46) and nitrogen (0.66) were the same over all nitrogen treatments. We found no evidence that shoot size per se controlled grain number or rate of grain growth; rather, fertilizer management during spikelet differentiation had most effect on yield of XL66.

Feeding high energy supplements to pasture-fed dairy cows. Effects of stage of lactation and level of supplement

Abstract: Five experiments were done in which stall-fed dairy cows were provided with a basal ration of pasture (6-7 kg DM) which was supplemented with varying amounts of a pelleted, high energy supplement (0-10 kg DM). Forty-seven cows at various stages of lactation were fed in this manner for up to 5 weeks. Responses to feeding the supplement depended on the stage of lactation at which the supplement was fed, and the amount of the supplement consumed. Marginal responses in milk production fell from 1.6 to 0.7 kg milk per kg supplement as lactation progressed, and as the level of feeding increased. Although responses in milk fat yield also decreased as lactation advanced, there was also a reduction in milk fat production when more than about 6 kg DM of supplement were fed. This was due to a severe depression in the fat content of the milk, which was found to be associated with intakes of diets with less than 250 g kg DM-1 neutral detergent fibre; diets with less than this level of fibre resulted in ratios of lipogenic to glucogenic volatile fatty acids in the rumen below 4:1. This occurred when the supplement constituted 0.4-0.5 of the diet on a dry matter basis. In addition, rumen ammonia levels were low when large amounts of supplement were fed. With all rumen characteristics, stage of lactation had no influence on values.

Relationship between net blotch (Drechslera teres) and losses in grain yield of barley in Western Australia

Abstract: Losses in the yield of cv. Dampier due to net blotch (Drechslera teres (Sacc.) Shoem.) were examined in six environments in Western Australia. Based on comparison between least diseased and most diseased treatments, there was an overall yield reduction of 21% (P < 0.05). Three models (Critical Point, Area Under Curve and Multiple Point) were used to study the relationship between net blotch infection and percentage yield loss. All models gave similar results. Because of its simplicity, the Critical Point Model based on mean net blotch infection on the top three leaves at GS 75 was chosen. The percentage yield loss in cv. Dampier was defined to be 37% of the mean diseased area on leaves 1 (flag), 2 and 3 at GS 75. This relationship is very similar to that developed earlier for scald, and a common equation for both scald and net blotch was suggested.

Salt tolerance in the genus Lolium (ryegrass) during germination and growth

Abstract: Two studies were undertaken, one to evaluate the degree of genotypic variation for salt tolerance within the Lolium (ryegrass) genus, and the other to compare the responses of three representative ryegrass species (Wimmera (L. rigidum), Italian (L. muttiforum) and perennial (L. perenne) ryegrass) with those of two known salt-tolerant grasses, tall wheat grass (Elytrigia pontica) and saltmarsh grass (Puccinellia ciliafa). Both germination and growth responses to increasing concentrations of NaCl were assessed under controlled environment conditions: seeds were germinated in petri dishes, and plants were grown in pots containing coarse river sand. In the first study, significant intra- and inter-specific variation for salt tolerance was demonstrated, particularly during germination. However, there was no apparent adaptation for salt tolerance in field collected accessions from saline sites. In the second study, all species were shown to be relatively insensitive to NaCl up to 200 mol m-3 during germination, but higher concentrations were tolerated only by saltmarsh grass, tall wheat grass and Italian ryegrass. Only the latter two grasses maintained their high tolerance during vegetative growth, whereas the ryegrasses were moderately tolerant. It was clear from both studies that relative salt tolerance ranking differed for germination and growth phases. Shoot concentrations of Na, Cl and K did not relate to the degree of salt tolerance.

Inheritance of resistance to Fusarium oxysporum f. sp. lycopersici races 2 and 3 in Lycopersicon pennellii

Abstract: An accession of Lycopersicon pennellii, PI414773, was resistant to race 2 isolate 18947 and race 3 isolate 14844 of Fusarium oxysporum f. sp. lycopersici. Tomato cultivar Contender, which is homozygous for gene 1-2, was resistant to race 2 but susceptible to race 3 of the pathogen. Cultivar Rouge de Marmande was susceptible to both race 2 and race 3. The inheritance of resistances to race 2 and race 3 in PI414773 was investigated in test crosses involving parents Contender, Rouge de Marmande and PI414773. Segregation of the F2 of the crosses Rouge de Marmande x PI414773 and Contender x PI414773 revealed that resistance to race 2 in PI414773 was controlled by two independent dominant genes, one of which is allelic with gene I-2. Segregations in F2, backcrosses and inbred backcrosses derived from Contender x PI414773 indicated that a single dominant gene conferred resistance to race 3. The symbol I-3 was proposed for this gene.

Leaf emergence rates of wheat in a mediterranean environment

Abstract: Rates of leaf appearance on the main stem were measured for various wheat varieties for five to ten sowing dates in three field experiments in Western Australia.Rate of leaf appearance was constant in relation to thermal time for any given variety and sowing date, and ranged from 0.0064 to 0.0132 leaves (¦C day)-1. Most of this variation could be accounted for as a response to sowing date or rate of change of daylength, although the response was complicated by interactions with variety and year.Because successive measurements were made on the same plants, it was possible to estimate directly the effects of temperature on the rate of leaf emergence. In the three years, mean rates of leaf emergence were 0.008, 0.008 and 0.011 leaves day-1 ¦C-1 with base temperatures (temperatures at zero rate) of 0.08, -1.2 and 0.4¦C respectively. Contrary to expectation, rate of leaf emergence decreased as temperatures increased in late sowings due probably to depression of leaf emergence as daytime temperatures exceeded 25¦C.For Gamenya, the only variety common to the three years, the rate of leaf emergence (RLE) on the main stem was related to the rate of change of daylength (-DL, min day-1 negative when daylength shortening) by the equationRLE = 0.00949 + 0.000988 (-DL).For crops emerging in late June (-DL approximately zero) in southern Australia, this implies a constant thermal time for leaf appearance of 105¦C day leaf-1.

Inoculation methods for assessing resistance in wheat to crown rot caused by Fusarium gramineum Group 1

Abstract: A range of inocululatron methods for assessing resistance in wheat to crown rot caused by Fusarium graminearum Group 1 was evaluated in the glasshouse and in the field. When grain was colonized with the pathogen, ground and applied with the seed at planting or spread around young plants as an aqueous suspension, high levels of crown rot were produced, but resistance (usually measured as per cent diseased plants or tillers) was still expressed. Similar results were achieved with induced field inoculum obtained by inoculating an area of wheat to obtain a high incidence of disease and incorporating the stubble into the soil. Natural field inoculum and inoculation of seed with spores produced lower levels of disease, although differentiation of resistant and susceptible cultivars was still possible. Other methods, suitable only for plants in pots and often for more specific purposes (for example, for inoculation at different stages of plant growth) were also studied. Resistance was best expressed where inoculum was applied onto or into soil, rather than directly onto or into plants. Currently, the resistance of all potential cultivars for release in Queensland is assessed in the field by sowing seed dusted with benomyl into furrows along which ground, colonized grain is distributed. Crown rot severity is then determined at maturity.

Barley yellow dwarf viruses in, and aphids on, grasses (including cereals) in Tasmania

Abstract: Samples of 2077 grasses and cereal plants representative of the Poaceae found in Tasmania were collected from a wide range of habitats throughout the State. Each sample was examined for infestation with aphids and then checked for infection with viruses causing barley yellow dwarf by both aphid transmission and serological tests. Aphid species found among the samples were Hyalopterus pruni, Rhopalosiphum maidis, R. padi and Sitobion fragariae. R. padi transmitted a vector non-specific type of barley yellow dwarf (PAV) and a vector specific type (RPV), either alone or together, while S. fragariae transmitted PAV alone and occasionally RPV when present in plants together with PAV. The other aphid species did not transmit. A total of 189 samples contained virus. Incidence was greatest in samples from the Bambusoideae subfamily (31%) and least in the Arundinoideae (4%). There was no difference in the level of infection between the native and introduced species that were represented. The Arundinoideae and Panicoideae were predominantly infected with RPV types, while the Pooideae, with the exception of Dactylis glomerata and Poa pratensis, were predominantly infected with PAV types. Many more infected plants contained both PAV and RPV (11.9%) than would have been expected had the two types of virus infected independently (2.5%). No infected plants were found among samples from 25 of the 56 species tested, and some of these may prove useful in breeding for resistance to barley yellow dwarf viruses.

Uptake and distribution of chloride, sodium and potassium ions and growth of salt-treated pistachio plants

Abstract: Plant growth rates and rates of uptake and root to shoot transport of chloride and sodium were compared between seedlings of the rootstock Pistacia atlantica Desf. and a scion cultivar P. Vera L. cv. Kerman treated with 30 mM NaCl for 63 days. Uptake and distribution of chloride, sodium and potassium ions were then investigated in P. atlantica and in another rootstock P. terebinthus L. subjected to periods of increasing salinity, commencing with 30 mM chloride and 18 mM sodium, and then increasing sequentially by these amounts every 3 weeks to reach a maximum of 150 mM chloride and 90 mM sodium. Shoot growth rates of P. Vera and P. atlantica were not affected by treatment with 30 mM NaCl. Rates of uptake and root to shoot transport of chloride were similar between the two species. However, the rates of uptake and root to shoot transport of sodium by P. atlantica were approximately 2-fold and 4-fold higher, respectively, than in P. vera. The chloride and sodium accumulated in the shoots of both species was diluted by growth, with the result that there was no marked increase in leaf and stem chloride and sodium concentrations in either species with time. After 63 days of salt-treatment, mean leaf chloride concentrations were less in P. atlantica, which had a higher relative growth rate and a higher shoot to root ratio than P. vera. Mean leaf sodium concentrations were higher in P. atlantica, reflecting the greater rate of root to shoot transport of sodium by this species. Sequentially increasing salinities up to a maximum of 150 mM chloride and 90 mM sodium had no significant effect on the dry matter production of P. atlantica and P. terebinthus. Laminae chloride concentrations of both species increased as the level of salinity was increased. Sodium concentrations in laminae of P. terebinthus showed a small but significant increase during treatment with the two highest salinity levels. Chloride concentrations on a tissue water basis were highest in laminae and petioles of salt-treated plants, whereas sodium concentrations were highest in roots, especially the proximal root, indicating retention of sodium in the lower part of the plant.

Environmental response of spring wheat in the south-western Australian cereal belt

Abstract: The performance of the spring wheat cultivar Gamenya, the leading cultivar in Western Australia since 1968, was studied to identify key aspects of its response to the environment under typically dry conditions on two contrasting soil types: a heavy clay loam and a light loamy sand overlying clay in the Merredin region. In the rain-fed treatments the total water use was similar on both soils and was of the order of 240 mm. On the heavy-textured soil at high nitrogen, the foliage canopy developed more rapidly than on the light soil, resulting in earlier soil water depletion and haying off. Water use efficiencies of about 10 kg grain ha- 1 per mm of water were similar to those reported for winter rainfall areas in south-eastern Australia. This suggests a greater degree of buffering against spring drought than is indicated by the high ratio of pre-anthesis to post-anthesis water use (3-4.7:l) relative to values of 2-2.7:l in other parts of the Aus- tralian wheatbelt. Data on the partitioning of dry matter indicated that this buffering of the harsh spring conditions at Merredin may be due to a greater contribution of assimilates from pre-anthesis storage, to grain filling. In dry environments, further critical evaluation is needed of the role of stored assimilates in grain formation. Faster canopy closure on the heavy soil resulted from a higher density of shoots and possibly larger leaves. This led to the suggestion that on heavier, more fertile soils, an ideotype with restricted tillering, may be higher yielding. By the end of the season ear bearing shoot densities and total water use were the same on both soil types, thus masking earlier important differences.

Poor early growth of wheat under direct drilling

Abstract: Poor early growth of wheat under direct drilling on a hardsetting duplex soil was studied in the light of a range of soil physical and biological properties. Two systems of direct drilling were included in the study: one with a short fallow maintained by herbicide (chemical fallow), and another in which a fallow period was absent and herbicide was applied 1 week before sowing (nil fallow). Plant measurements indicated that the poor early growth observed under both direct drilled systems, as compared to that under conventional cultivation, was not due to poor germination or poor emergence. Rather, it was shown to be a consequence of reduced growth after establishment. Weight per plant measured 64 days after sowing for the conventional, chemical and nil fallow treatments was found to be in the ratio of 3.2: 1.8 : 1.0, respectively. Soil physical measurements during the 9 weeks from sowing indicated that moisture availability was unlikely to be an important factor affecting the observed growth difference for the particular season. Much higher bulk density (1.66 versus 1.35 Mg/m3 at 50-100 mm) and vane shear strength values were found in the undisturbed soil between the drill rows in the top 100 mm of the two direct drilled treatments. Vane shear strength measured in the top 50 mm layer of the direct drilled plots was up to 2.9 times higher between the drill rows than in the drill rows. The poor vegetative growth on the chemical fallow plots was probably caused by restricted root growth in the denser and stronger 0-100 mm depth of undisturbed soil. The poor early vegetative and root growth of wheat in the nil fallow could not be fully explained by the soil physical properties, but indicated the presence of other root inhibitory factors. Our results suggest that one such factor is the presence of inhibitory Eacteria on the roots.

Leaf acid phosphatase isozymes in the diagnosis of phosphorus status in field-grown wheat

Abstract: This study examined the inorganic and total phosphorus in wheat plant tops, along with the phosphatase activity and the phosphatase isozymes occurring in the youngest fully expanded leaves, from two field experiments done in 1983 and I984 at two sites in South Australia. Twelve levels of phosphorus were used in the first year, and split plots in the second year allowed the effects of current and/or residual phosphorus treatments to be determined.The inorganic or total phosphorus concentration, or content per plant, could be related to plant and grain yield, but values relative to phosphorus deficiency varied between different stages of growth and between sites. Relationships with inorganic phosphorus were no better than those with total phosphorus.Leaf acid phosphatase assays were a better measure, providing similar values relative to plant deficiency between sites, between seasons and irrespective of whether current or residual phosphorus was the source, but the values varied with plant age.The phosphatase zymograms identified an isozyme which appeared when plants were deficient in phosphorus. It did not appear when they were adequately supplied. The isozyme appeared at all stages of growth to anthesis, and from late tillering through to heading was related to grain yield at both sites, in both seasons and whether freshly applied or residual phosphorus was the source of supply. For diagnostic purposes, specific sets of standards would be required for the phosphorus and phosphatase assays. They would not be required for the phosphatase zymograms.

Studies with the Australian Cashmere Goat. I. Growth and digestion in male and female goats given pelleted diets varying in protein content and energy level

Abstract: Some aspects of growth and digestion were studied in Australian cashmere goats in two experiments. In the first experiment, weaner goats (initial LW 13.4 kg) were given three ground and pelleted diets (11.3, 16.0, and 20.9% crude protein) at two levels of intake. Growth rates were highest in males fed the high protein (HP) diet ad libitum (149 g day-1) and lowest in females consuming the low protein (LP) diet at restricted intakes (30 g day-1). Increasing the protein content of the diet resulted in significantly greater liveweight gains, although the improved growth could be largely attributed to increased intake rather than to enhanced feed efficiency. Males grew faster, retained more nitrogen and used feed with greater efficiency than did females. A second experiment with fistulated goats (mean liveweight 16.4 kg) fed the LP and HP diets from experiment 1 showed that organic matter (OM) digestion was greater in goats fed the LP diet (67.9% v. 65.3%). In contrast, the proportion of OM digestion which occurred in the stomach was greater for goats fed the HP diet (76.7 v. 57.4%). For both diets all of the cellulose and hemicellulose digestion took place in the rumen; however, substantial amounts of starch escaped rumen digestion. Large losses of nitrogen across the rumen (4.9 g day-1) in goats given the Hp diet resulted in reduced flows (11.1 g day-1) of non-ammonia nitrogen (NAN) to the small intestine, compared with the LP diet (12.7 g day-1). Digestion of NAN in the intestines was greater in animals consuming the LP diet, possibly reflecting the greater intestinal contribution made by non-microbial NAN. For both diets the ratio of protein to energy available (11.0 and 10.2 g protein MJ-1 ME for LP and HP diets respectively) was estimated to be in excess of maximum tissue requirements for growth.

The effect of boron supply on the growth and seed production of subterranean clover (Trifolium subterraneum L.)

Abstract: There has been little research on the boron (B) status of subterranean clover, despite strong indications of deficiency of B in southern Australia where clover decline has been reported. This paper describes glasshouse experiments to vary the level of B supply to clover grown on soils low in B. On a soil farmed in a cereal clover rotation, herbage yields of clover increased by 25% with applied B, but seed yields, negligible without B, increased 21-fold. On two other acid soils, from pastures, there were also large responses to B in seed yield (1.5- and 5.1-fold respectively); liming increased the responses (8- and 55.2-fold). However, herbage production was less responsive to B (25% and 1.7-fold with liming); on the unlimed soils, application of B depressed yield (- 1 and -21%). This is attributed to there being enough B to sustain herbage growth, but inadequate for seed formation. These results show that herbage yield, conventionally employed in the past, is not a satisfactory index of B status for total performance in subterranean clover. The response to B in seed yield was associated with increases in: numbers of seed set (75% to 22.6-fold, depending on the particular combination of soil and liming); size of seed (10% to 1.2-fold); proportion of buried seed (20%-70%). It is suggested that these favour establishment and persistence of clover and that clover decline may well involve deficiency of B. It was shown that concentration of B in the plant does not necessarily relate predictably to yield of herbage and that reduction in seed yield may not be heralded by foliar symptoms, since seed requirement exceeds that of herbage.

Factors affecting the hydrogen cyanide potential of white clover (Trifolium repens L.)

Abstract: Pot experiments were used to determine the effects of age, light, temperature, mineral nutrition and wilting on the HCN potential (HCNp ) of white clover (Trifolium repens L.). HCNp, adjusted for pre-expenmental HCNp, was reduced by higher light intensity (505 v. 220 mg HCN kg-1 DM), by increased temperature (408 v. 317 mg HCN kg-1 DM) and by phosphorus application (382 v. 343 mg HCN kg-1 DM). These effects were largely explained by the hypothesis that HCNp diminished as the size and vigour of the plant increased, and the use of dry matter production as a covariate on HCNp removed the significant effects of light, temperature and phosphorus. In two experiments wilting plants prior to harvest increased HCNp by 15 and 24%, and reduced dry matter yield by 9 and 13%. HCNp declined curvilinearly as the white clover aged. The conditions shown to favour high HCNp, namely, immaturity, moisture stress, low light intensity, cool temperature, and inadequate P supply, are those which occur periodically in the late autumn and early spring of temperate climates. Sheep in late pregnancy at this time, could, if white clover comprises a substantial proportion of their diet, experience thiocyanate absorption as a consequence of HCN detoxication and hence increase the risk of goitri to the lamb.

Responses to nitrogen and maize supplements by young cattle offered a low-quality pasture hay

Abstract: Twenty-seven Hereford steers (227¦3 kg) were offered ad libitum low-quality grass pasture hay containing 4.3 g N/kg DM. These steers were offered one of three maize supplements (nil, 570 g/day crushed maize or 680 g/day whole maize) alone or with one of two nitrogen (N) supplements (1 12 g/day urea: 250 g/day molasses, or 800 g/day pelleted protein meals). The crushed maize, whole maize and protein meal supplements were calculated to be isoenergetic on a metabolisable energy basis, and the urea and protein meal supplements were isonitrogenous.Both urea and protein meal supplements increased the intakes of hay and total digestible organic matter (DOMI), but there was a significant interaction between maize and N supplements such that maize increased hay and DOM intakes when offered alone. Unsupplemented steers ate only 1.98 kg OM of hay/day, whereas N supplemented steers ate 3.96-4.40 kg OM/day, and those supplemented with crushed and whole maize alone ate 2.45 and 2.85 kg OM/day respectively. The intakes of hay by the urea and protein meal supplemented groups were not significantly different.Both N and maize supplements had positive effects on liveweight change (P < 0.01), with N having the largest effect. Steers supplemented with protein meal gained 210 g/day more than those offered urea (P < 0.05), although DOMI was only 110 g/day more, indicating an effect of protein on the efficiency of utilisation of absorbed nutrients.N supplements increased rumen ammonia concentrations from 10¦3.0 mg NH3-N/l in unsupplemented steers to 169¦ 19.3 and 105¦ 19.0 mg NH3-N/l in steers offered urea and protein meal respectively; there was a significant interaction between the form of N supplement and form of maize supplement (P < 0.05). Total volatile fatty acid concentrations in the rumen (65¦ 1.9 mM) did not differ significantly between supplements.Glucose entry rate was positively related to liveweight change and was increased by both the N supplements and whole maize. Glucose entry rate, adjusted for DOMI, was higher in protein meal supplemented steers than those receiving urea or no N supplement (P < 0.01), and these steers had the highest growth rate.Urea pool size, and synthesis rate in the body, were greater in steers given the urea and protein meal supplements (P < 0.05), but there were no significant differences in these measurements between urea and protein meal supplements.

Seasonal Variation in the Infectivity of VA Mycorrhizal Fungi in Annual Pastures in a Mediterranean Environment

Abstract: The seasonal variation in the rate and extent of formation of mycorrhizas in pasture soils from two sites in south-west Australia was examined. Undisturbed soil cores were taken on eight occasions throughout the year, sown with Trifolium subterraneum L. and maintained in a glasshouse. At each collection time the extent of formation of mycorrhizas was measured 3 and 6 weeks after sowing. There was no seasonal variation in the extent of mycorrhizas formed in undisturbed soil cores at one site, hut at the other site the extent of mycorrhizas decreased over time. The rate of formation of mycorrhizas was most rapid when cores were collected immediately after the opening rains of the season. Similar species of fungi were present at both sites; however, the rate and extent of infection formed by each species differed between the sites. At both sites the infectivity of A. laevis and fine endophyte decreased throughout the winter months, but the infectivity of GIomus spp. did not change. Neither the total spore number nor an estimate of the number of infective propagules reflected the infectivity of the total population of VA mycorrhizal fungi measured simultaneously at the two sites.

Indigofera species with agronomic potential in the tropics. Rat toxicity studies

Abstract: Lack of information on the feeding value and on the presence of deleterious substances in many species belonging to the genus Indigofera has limited the potential use of these species as feed and fodder legumes. To obtain such information, leaves and seeds of 46 accessions representing 19 species of Indigofera that had shown some agronomic value were incorporated into a semi-synthetic diet at 5% w/w (seed) or 20% w/w (forage). The diets were fed to groups of young rats for 4 weeks, and dry matter intakes and growth rates relative to control diets were measured. Selected organs were examined for any histological changes. Seed and forage samples were analysed for indospicine, a hepatotoxin, and for the presence of another potentially deleterious substance, 3-nitropropanoic acid. Thirteen of the accessions representing 8 species were readily eaten and did not depress growth rates relative to control feeds, and another 13 representing 10 species gave acceptable growth rates. Liveweight gains were less affected by forage diets than by those containing seeds. With the exception of those in rats fed on diets containing I. spicata and I. nigritana, the organs of all other rats were histologically normal. It is unlikely that the concentration of 3-nitropropanoic acid (0.5-3.4 mg g-1 dry matter) in any feed was high enough to cause any of the observed toxic signs. Indospicine was present in only 4 of the 23 species tested, including all accessions of I. spicata, and the concentration of indospicine was a good indicator of the toxicity of these feeds. It is concluded that accessions that had produced growth rates comparable to those of controls may be recommended as non-toxic feeds suitable for further testing.

Effects of direct drilling on the phosphorus uptake and fertilizer requirements of wheat

Abstract: The effect of direct drilling on the phosphorus (P) relations of ~vheatw as examined in seven field experiments over three years. Compared with conventional cultivation of the soil, direct drilling concentrated available phosphorus nearer the soil surface and resulted in higher strength and lower root length in surface soil (0-10 cm). Tissue-P concentration and dry weight of young plants (< 10 weeks) were consistently lower after direct drilling. It appeared therefore that direct drilling limited the uptake of soil phosphorus. An unknown factor also reduced plant dry weight per unit of P taken up in some experiments, whilst high rates of P fertilizer generally failed to give equal P concentration or dry weight in early growth. It is suggested that the young plants were unable to exploit fully the banded fertilizer because of insufficient adaptation of roots to the concentrated source of P and that this effect is a greater disadvantage for a direct-drilled crop. Direct drilling gave lower grain yields in four experiments when no fertilizer was applied, but where rates of P fertilizer were high, the two tillage treatments produced equal'pields. In these four experiments direct-drilled crops needed more fertilizer to attain 90% of the maximum yield. Crops in cultivated soil had the higher dry weight at anthesis and therefore the higher potential yield at equal rates of P fertilizer (in two years), but they failed to realize their potential at high rates of fertilizer because their greater vegetative growth led to increased water stress after flowering.