High Rainfall Sites Research Articles

Differential tolerance of Trifolium subterraneum L. (subterranean clover) cultivars to broadleaf herbicides. 2. Seed yield and quality

The effect of broadleaf herbicides on seed set by Trifolium subterraneum (subterranean clover) cultivars was examined at 2 sites (Wagga Wagga and Canowindra) over 2 years. Five commonly used herbicide treatments (bromoxynil, MCPA, 2,4-DB, MCPA + terbutryn, MCPA + diuron) were applied at 2 rates to 7 cultivars of subterranean clover. Significant site x cultivar x herbicide interactions were observed. Seed yields were either unaffected or depressed by up to 66% at the higher rainfall site (Canowindra), whereas at the lower rainfall site (Wagga Wagga) some herbicide x cultivar combinations showed increases in seed yield up to 115%. The increase in seed yield was greater at the lower herbicide rate. The variation in seed yield with herbicide treatment was largely a result of a change (P<0.001) in the number of seeds set (R = 0.94 at Wagga Wagga; R = 0.85 at Canowindra). Seed size was also correlated (P<0.001) with seed yield at both sites but explained less of the variation (R = 0.23 at Wagga Wagga; R = 0.47 at Canowindra). The reduction in herbage yield as a result of herbicide application was a poor indicator of the subsequent seed yield response at both sites. Cultivar Trikkala was consistently most tolerant to the herbicide treatments, showing either no change in seed yield at the wetter site or large increases in seed yield at the lower rainfall site. In contrast, the seed yield of Dalkeith was depressed by 2,4-DB at both sites in both years by 39-66%. Increases in seed yield, which were most pronounced in cultivars of midseason maturity (Trikkala, Junee, Seaton Park) and least in later maturing cultivars (Karridale, Clare) and in the very early flowering Dalkeith, were attributed in part to a water-saving effect of the herbicide treatments. Cultivar maturity ranking was negatively correlated (P<0.001) with seed yield (R=-0.73 at Wagga Wagga; R=-0.45 at Canowindra). The germination percentage of seed produced by the cultivars was unaffected by herbicide treatment, although the number of abnormal radicles formed by germinating seed was higher in the 2,4-DB and MCPA treatments.

Influences of Trees on Savanna Productivity: Tests of Shade, Nutrients, and Tree‐Grass Competition

To determine why herbaceous productivity in tropical and subtropical savannas is often significantly higher under crowns of isolated trees than in adjacent grass—lands, experimental plots were established in three concentric zones, crown, tree—root, and grassland, surrounding isolated trees of Acacia tortilis in low—rainfall and high—rainfall savannas in Tsavo National Park, Kenya. Plots were fertilized (to determine the importance of nutrient enrichment by trees), shaded (to determine the importance of crown shade), fertilized and shaded (to identify fertilizer x shade interactions), or trenched (tree roots entering plots were severed to determine the importance of belowground competition between overstory trees and understory herbaceous plants). In addition, vertical root distributions of trees and herbaceous species were determined, and root systems of A. tortilis saplings were excavated. At both sites fertilization significantly increased herbaceous productivity in tree—root and grassland zones, but not in canopy zones; artificial shade had no effect on productivity at the low—rainfall site but increased productivity in the tree—root zone at the high—rainfall site; and severing tree roots had no effect on herbaceous productivity at the low—rainfall site, but increased productivity in the crown and tree—root zones at the high—rainfall site. Roots of herbaceous and woody species co—occurred within the same soil horizons, but tree roots extended farther into grasslands at the low—rainfall site than at the high—rainfall site. These studies suggest that savanna trees completed more intensely with understory plants at wetters sites, where their roots terminated in or near crown zones, than at drier sites, where their roots extended farther into open grassland. Nutrients added by trees to crown zones in the form of tree litter and animal droppings increased understory productivity by fertilizing nutrient—limited soils. Shade contributed more to regrowth after severe defoliation than to growth under more normal conditions.

Productivity and nitrogen fertilizer requirements of barley in rotation systems in rainfed mediterranean conditions

The productivity of barley was examined, when grown after vetch or fallow or in continuous barley systems, at two locations in Cyprus (250 and 350 mm mean annual rainfall sites), for eight years. Barley was supplied with 0, 30, 60 or 90 kg N ha-1 fertilizer in sub-plots. Barley in the vetch-barley and fallow-barley systems was more productive than in continuous barley systems. Nitrogen fertilizer applied to continuous barley was not sufficient to compensate for the rotation effect that vetch (at both locations) and fallow (at the 250 mm site) had on the subsequent grain yield of barley. At both sites, the optimum N fertilizer rate for grain yield of barley was zero and 30 kg N ha-1 when grown after vetch and fallow, respectively, while after continuous barley systems it was 45 and 60 kg N ha-1 for the low and high rainfall sites, respectively. In comparison to a continuous barley system, the fertilizer replacement value of vetch for the subsequent barley was 60 kg N ha-1, and that of fallow 30 kg N ha-1. Nitrogen and water storage were the major factors contributing to the total rotation effect on barley yield after vetch and fallow, even though other unidentified factors were also involved.

Sulfonylurea herbicides applied to acidic sandy soils: movement, persistence and activity within the growing season

Chlorsulfuron and triasulfuron were applied to the surface of acidic, sandy loam at a low rainfall site in 1989 (129 mm June-October) and a high rainfall site in 1990 (217 mm July-August). Four environments were obtained by early and late application times and lime addition in 1989 and by a wetter site in 1990. The pH of the surface 10 cm was 4.9 in 1989, 5.8 in 1990 and 6.5 after the addition of limestone in 1989. The plots were left fallow or sown, prior to herbicide applications, to wheat (cv. Kulin). Hourly averages of rainfall, soil and air temperature were recorded. The temperature range was 2.7�C to 23.2�C. The soil profiles were sampled on 5 to 7 occasions and herbicide residues were determined by a laboratory bioassay (sensitivity >0.4 8g kg-1 soil). Chlorsulfuron and triasulfuron were detected to 300 mm in the wetter environment but neither herbicide was as mobile in the profile as water. More herbicide moved to the lower layers of the profile in the higher pH environment. The half-lives for residues ranged from 12 to 28 days. Shoot biomass of wheat seedlings was suppressed by both herbicides but grain yields were unaffected. The residues failed to prevent reinvasion of the wheat plots by weeds, notably Arctotheca calendula.

Rainfall interception by trees of Pinus radiata, and Eucalyptus viminalis, in a 1300 mm rainfall area of southeastern New South Wales: I. Gross losses and their variability

AbstractInterception loss, I, was determined by continuous concurrent measurements of the canopy precipitation balances of a mature seed orchard tree of Pinus radiata, and a dominant tree of Eucalyptus viminalis at a mountainous high rainfall site (900 m a.s.l.) in Tallaganda State Forest of the Upper Shoalhaven Catchment. Approximate canopy storage capacity (Sc) of the pine was 54 l, and that of the eucalypt was 11·3 l. Gross pine I was 26·5 per cent and eucalypt I was 8·3 per cent of total incident rainfall over a period of 18 months, from June 1975 to December 1976. The exponential model that provided the best fit to overall data relating I to gross rainfall (Pg) was of good precision for the pine (r2 = 0·73) but rather poor precision for the eucalypt (r2 = 0·27). A consistent pattern in interception data of the two canopy types suggested that variation in I was related to change in pervasive conditions influencing rates of evaporation from wet canopies during rainfall. Multiple regression analyses confirmed that factors such as rainfall intensity and windspeed explained some of the variation in eucalypt I but little in pine I.Negative eucalypt I and corresponding low values of pine I over a wide range of Pg (up to 20 mm) suggest that capture of wind‐borne precipitation (cloud, mist, or fog) had also complicated the canopy precipitation balances.

Effects of summer grazing and fertiliser on the clover content of hill country swards in the Gisborne region

Preliminary results are presented from an investigation to identify reasons for the low clover content of hill country pastures in the Gisborne-East Coast region. Four experiments were established near Gisbome. Treatments included: fertiliser versus no fertiliser; summer grazing versus no summer grazing; and clover cultivars (transpanted into swards). Summer rainfall had the major influence on the clover content of swards. With a reliable high summer rainfall the clover content averaged 16% of herbage. By contrast, with less reliable and lower summer rainfall, the clover content averaged 4-5% and subterranean clover was more important, Summer spelling of pasture, which allowed rank grass growth, reduced both white and subterranean clover content of swards. Fertiliser inputs increased the clover content of swards. Performance of cultivars was affected by grazing, differences between cultivars being greatest with summer grazing. The small-leaved cultivars of white clover ('Grasslands Tahora' and 'Whatawhata') initially performed better than larger-leaved cultivars at the high summer rainfall site, but failed to sustain any advantage. 'Tallarook' subterranean clover increased the clover content of swards with summer grazing. Keywords white clover, subterranean clover, East Coast, hill country, fertiliser, grazing management

Nutrient content of bulk precipitation in south-central Java, Indonesia

AbstractThe chemical composition of bulk precipitation was studied for a period totalling 18 months between 1975 and 1978 at a high rainfall site in central Java. The following elements were determined: calcium, magnesium, sodium, potassium, nitrate-nitrogen, chlorine, phosphate-phosphorus, silicon, aluminium, iron, manganese and pH. Ammoniacal nitrogen, total nitrogen and sulphate-sulphur were determined, during four weeks in May 1983. Concentrations of all elements rose dramatically during the exceptionally severe dry season of 1977 which may have caused accession rates for some nutrients to be overestimated (i.e. compared to a year with ‘normal’ rainfall) by about 10%. Results are explained in terms of prevailing wind directions and proximity to, or absence of, particular solute sources, such as the ocean, volcanoes or eroding lands.Most elements exhibited intermediate concentrations when compared with data for other humid tropical locations; sodium and perhaps nitrogen were on the low side and pH on the high side of the spectrum. Annual accession rates at the study site were considerable by pan-tropical standards, mainly as a result of high rainfall totals. Comparing accession rates with 25-year-average nutrient immobilization rates in stemwood of local plantations ofPinus merkusiiJungh. et de Vr. andAgathis dammaraWarb. showed atmospheric inputs of magnesium and potassium to be high enough (theoretically) to account for losses of these elements in stemwood removal. Corresponding figures for nitrogen were 90% (Pinus) and 50% (Agathis), and for calcium and phosphorus 60 and 40% respectively (both species).

7Be deposition in a high-rainfall area of New Zealand

Concentrations of natural 7Be in air and rainwater were monitored for one year at Hokitika, New Zealand. The mean airborne concentration was 3.1±1.3 mBq m−3, the mean Hokitika, New Zealand. The mean airborne concentration was 3.1±1.3 mBq m−3, the mean concentration in rainwater was 2600±1200 Bq m−3, and the mean total deposition was estimated to be 130±99 Bq m−2 wk−1. Most of the 7Be was wet deposited and the washout ratio was independent of precipitation amount. A significant linear relationship exists between the weekly wet deposition flux and weekly precipitation at this high-rainfall site.

Genetic diversity in Old Subterranean Clover (Trifolium subterraneum L.) Populations in Western Australia. I. Pastures sown initially to the Dwalganup strain

Subterranean clover burrs were collected during summer from 28 sites, 10 of which were in the <500 mm annual rainfall zone. All sites had been sown to the Dwalganup strain, 30-50 years ago. Spaced plants were grown from seed from burr subsamples of each population. Several morphological characters, flowering dates, and oestrogenic isoflavones in late spring leaf samples were determined. At maturity, burr samples were collected from each plant, and the isozyme patterns in seeds were determined for eight enzyme systems using starch gel electrophoresis. Populations from the lower rainfall (< 500 mm) sites usually consisted of one or two strains - Dwalganup with or without Geraldton - and variant (or 'unknown') genotypes were very rare or absent. Populations from the higher rainfall (> 500 mm) sites, on the other hand, comprised about 50% of a few known strains - mostly Dwalganup and/or Dinninup - the remaining 50% consisting of numerous variant genotypes. Infrequent outcrossing between the Dwalganup and Mt Barker strains is the likely major source of this variation. Possible explanations for the lack of variant genotypes in the lower rainfall zone are discussed.

Environmental isotope hydrology of salinized experimental catchments

Deuterium, oxygen-18, tritium and chloride concentrations were used in three salinized experimental catchments to gain insight into the mechanism of solute concentration and flow processes in the saturated and unsaturated zones. The three experimental catchments were studied because of their location in different rainfall regions, their status with respect to clearing of native vegetation and with respect to secondary salinization. Two uncleared catchments have average annual rainfalls of approximately 820 and 1220 mm, respectively. The third cleared catchment has an annual rainfall of 650–750 mm. This catchment was in an advanced state of secondary salinization and displayed large areas of saline groundwater discharge with halite encrustation at the ground surface. The stable isotope compositions of the solution phase in solute bulge profiles in the unsaturated zone showed a close agreement with the amount-weighted mean isotopic composition of rainfall and only surficial evidence of isotopic enrichment due to evaporation. Evaporation from the soil surface plays a minor role as a mechanism of solute concentration in the unsaturated zone. The dominant process of solute concentration in the unsaturated zone was ion exclusion during uptake of water by tree roots which was evidently a solute but not isotope fractionating process. Tritium analyses of unsaturated zone water and grondwater indicated movement of recent recharge to 7–10 m depth at the low rainfall site but over the full depth of the 15 m unsaturated zone at the higher rainfall site. The variability in δ 18O and δ 2H values of groundwaters was used in association with chloride concentrations to provide information on mixing characteristics of groundwaters within the catchments.

Ecology of a Grazing Ecosystem: The Serengeti

Primary productivity and herbivory were studied in the Serengeti National Park, Tanzania, and Masai Mara Game Reserve, Kenya, during the annual cycle of 1974—1975, and wet—dry season transitions in 1976—1979. Basic state variables measured were aboveground plant biomass inside permanent and temporary fences, and outside fences. Productivity was calculated as the sum of positive plant biomass increments. Control productivity (cPn) was calculated from biomass dynamics inside permanent fences. Temporary fences were moved in concert with grazing by the region's abundant ungulates to estimate actual aboveground primary productivity (aPn). Primary productivity was highly stochastic with productive periods poorly synchronized even among nearby sites. Short—term productivities could be extremely high, exceeding 30 g°m—2°d—1. Grazing animals adjusted their densities in relation to grassland productivity. The average proportion of annual aPn that was consumed by herbivores was 0.66, with a minimum of 0.15 and a maximum of 0.94. Green forage was available everywhere late in the wet season in May but was available only at high rainfall sites in the northwest late in the dry season in November. By the end of the dry season, the residual plant biomass outside fences averaged only 8% of cPn. Nomadic grazers moved seasonally in response to grassland productivity. The growing season ranged from 76 d in low rainfall areas to virtually continuous in high rainfall areas. Annual cPn was linearly related to rainfall and averaged 357 g°m—2°yr—1 over the year and 1.89 g°m—2°d—1 during the growing season. Actual aPn was substantially greater than cPn at most sites, averaging 664 g°m—2°yr—1. Growing season aPn averaged 3.78 g°m—2°d—1. Grazing stimulated net primary productivity at most locations, with the maximum stimulation at intermediate grazing intensities. Stimulation was dependent upon soil moisture status at the time of grazing. Rain had a diminishing effect on primary productivity as the wet season progressed and plant biomass accumulated. Part of the stimulation of grassland productivity by grazing was due to maintenance of the vegetation in an immature, rapidly growing state similar to that at the beginning of the rainy season. Since grazers overrode rainfall—determined productivity patterns, aPn was more closely related to grazing intensity than to ranfall. Grazing was heavier on grasslands that were intrinsically more productive. Rate of energy flow per unit of plant biomass was much higher in grazed vegetation. Grazers ate green leaves almost exclusively during the wet season, but species composition of the diets of different grazers differed markedly. Diets of nomadic grazers were very different in the wet and dry seasons. Vegetation dried out rapidly at the onset of the dry season and dry plant tissues made up a substantial proportion of ungulate dry season diets. However, green forage commonly was more abundant in diets than in the vegetation. Grazing increased both forage quality and its rate of production. Zebras supplemented a high—bulk diet by eating the seeds of awnless grasses. The foraging patterns of different grazers were differentiated by several vegetation properties, including productivity, structure, and species composition, in a manner suggesting resource partitioning. The relationship between the stability of vegetation functional properties and community species diversity was positive in five of seven tests. Greater species diversity was associated with greater biomass stability through the seasons, greater resistance to grazing by a single species of ungulate in both the wet and dry seasons, and greater resilience after grazing. Species diversity was not associated with greater resistance to grazing by several ungulate species or to plant species extinction. Specific properties of trophic web members were identified that produced greater functional stability in more diverse communities. Fire does not appear to have important effects upon the functional properties of the grasslands except for a weak stimulation of productivity in the wet season immediately following dry season burning. Fire did have an important effect upon structural properties of the vegetation that would tend to regulate ungulate feeding. The ecology of neither the plants nor the animals in the Serengeti ecosystem can be understood in isolation; many traits of both suggest coevolution among trophic web members. The functional dynamics of the trophic web suggest that the acceleration of energy and nutrient flow rates due to intense herbivory has resulted in the development of an entire consumer food web due to additive fluxes rather than mere quasi—parasitic fluxes from plants to animals.

The capeweed content of pastures in south-west Western Australia

The capeweed (Arctotheca calendula) content of pastures in the agricultural areas of Western Australia was estimated from coloured aerial photographs taken during flowering. Linear regressions were obtained between a visual score for capeweed content based on colour and the actual capeweed content of calibration sites. Surveys in 1972, 1973 and 1975 showed that 1973 was a year of high capeweed content in all areas compared with 1972 and 1975. The content was higher in lower-rainfall wheatbelt areas, where it averaged about 50% of pasture dry matter in 1973, than in the high-rainfall grazing areas, where the average was 37%. Fluctuations from year to year were followed on fixed sites between 1973 and 1977. The high rainfall sites varied more from year to year in capeweed content than did the low-rainfall sites. A detailed survey of one farm was made between 1972 and 1976 and this confirmed the indications from the other broadscale surveys that 1973 and 1976 were years that favoured capeweed. They were years when germination was followed by a 4-5 week dry period. Soil type and position in the landscape were also shown to influence the capeweed content of pastures.

Effect of Summer Moisture Stress on the Capacity of Tansy Ragwort (Senecio jacobaea) to Compensate for Defoliation by Cinnabar Moth (Tyria jacobaeae)

SUMMARY (1) Tansy ragwort plants were grown under different irrigation regimes to assess the effect of summer moisture stress on their capacity to compensate for defoliation by larvae of the cinnabar moth. Three measures of compensation capacity increased with increasing frequency of irrigation: the amount of growth produced following defoliation, the number of nodes which produced this growth, and the number of flower heads (capitula) produced following defoliation. Thus moisture availability limited plant compensation under these experimental conditions. (2) Compensation capacity was positively correlated with moisture availability in (a) comparisons of populations at a high summer rainfall site and a low summer rainfall site and (b) comparisons of populations during wet and dry years. Thus moisture availability appeared to limit plant compensation under natural as well as experimental conditions. (3) These results indicate that the full potential of the cinnabar moth as a biological control agent of tansy ragwort will be apparent in years with below average summer rainfall. In wet areas the introduction of additional biological control agents should be considered. Investigation of the influences of abiotic conditions on the interactions between plants and their herbivores may be necessary in other studies concerned with predicting the outcome of this interaction.

Rapid changes in simple mixtures of Townsville stylo (Stylosanthes humilis) lines differing in flowering time and growth habit

The ecological adaptation of Townsville stylo (Stylosanthes humilis) lines was studied by following changes in the composition of mixtures of the lines. At Weipa, a high rainfall site in north Queensland, the composition of a mixture of four maturity types changed rapidly in favour of the later flowering lines, and the earliest line was almost eliminated by the end of the second year. In binary mixtures at 'Lansdown' near Townsville, defoliation every six weeks favoured erect lines but the proportion of prostrate lines was almost doubled at the three week cutting frequency. Changes in mixture composition could not be related to the dry matter yield or pod yield of the monocultures at either site. The capacity of late flowering lines to increase rapidly in populations growing in high rainfall areas, as demonstrated at the Weipa site, could pose problems for the commercial seed production of earlier flowering lines in such areas.

A comparison of twenty-seven introduced grasses in two dry-tropical environments in northern Queensland

In a grazed sward trial to compare dry matter production from 25 grass accessions fertilized with 250 kg ha-1 urea annually over a period of four years at 'Lansdown', the highest yielding grasses were Cenchrus ciliaris (buffel grass) cvv. Nunbank and Biloela. Chloris gayana (Rhodes grass) accession 16059, Panicum maximum (green panic) cv. Petrie and C. gayana cv. Callide in that order. Several species failed to persist and some accessions of Chloris, Paspalum and Melinis were virtually non-existent by the end of the second season. In another experiment comparing dry matter production under grazing of 23 accessions sown with a standard legume mixture at two sites ('Lansdown' and 'Fanning River') over periods of five and four years respectively, the highest yields were obtained from Urochloa mosambicensis 6559, C. ciliaris cv. Tarewinnabar and accession 18019 at both sites. Urochloa was top yielder in the higher rainfall site at 'Lansdown' and the two buffel grasses were best at the drier site 'Fanning River'. Of the 23 accessions sown, only 12 at 'Lansdown' and only 7 at 'Fanning River' were persisting strongly when the experiment was completed. Grasses common to both experiments at 'Lansdown' were higher in nitrogen when grown with associated legumes than when grown alone and fertilized with urea. Grass nitrogen levels were low enough to reduce intake by cattle of nearly all accessions throughout the growing season under the urea fertilizer system and phosphorus levels in the grass were generally below that considered adequate for animal nutrition in the legume plots; however, the legumes would probably supply sufficient to meet the animal's requirements for at least part of the year. At 'Fanning River' the accessions were generally lower in nitrogen and phosphorus than at 'Lansdown'.