Hydro-sedimentology of the Johnstone River estuary

This paper examines the physical consequences of increased catchment sediment yields on the sediment budget and the hydrodynamic setting of the South Johnstone River estuary in North Queensland. A combined study involving hydrological monitoring, assessment of sediment sources, estimation of riverine sediment budget and hydro-sedimentological numerical modelling for estuarine sediment transport is currently underway. Initial field and laboratory observations indicate that the sediment delivery from highly erosion-prone sugar cane cultivations in the tropical catchment has increased dramatically during the last 10 years. This has subsequently given rise to elevated flood levels in both the lower and upper catchment areas, as well as significant modifications to the river bed morphology.     

Sensitive bioassays for determining residues of sulfonylurea herbicides in soil and their availability to crop plants

Sulfonylurea herbicides are potent inhibitors of plant growth and are extremely active against a wide spectrum of weeds. They are used at very low rates (10–50 g ai/ha) and cause rapid inhibition of root and shoot growth of young plants. Routine chemical assays for detecting low levels of these compounds are difficult and there is need to develop sensitive bioassay methods for detecting their extremely low residue levels in the soil.This paper describes a simple pot bioassay method with a self watering system using turnip (Brassica rapa) seedlings as test plants for quantitative determination of sulfonylurea herbicides. Results are presented with six of these compounds whose activity was investigated in widely differing substrates. The potential availability to plants was calculated from the dose-response curves in different substrates. The dose-response relationship has been described by a specifically developed computer model. Details are also given of a direct seeded bioassay method with controlled watering system using several test species for detection of sulfonylurea herbicides. The potential uses and practical applications of both techniques are discussed.     

The selection of microbial communities by constant or fluctuating temperatures

Abstract The diversity of bacterial communities isolated from Antarctic lake sediment in chemostats under constant low temperature (8°C) or diurnally fluctuating temperature (1°C to 16°C) was examined. The median optimum temperature for growth of the freshwater bacteria isolated from the fluctuation chemostat was significantly lower ( P < 1%) than that for those from the constant temperature chemostat. The diversity of the enriched bacterial community isolated in the chemostat culture subjected to short-term temperature fluctuations was greater than that enriched under constant temperature. At least 4 different groups of bacteria, that occupied separate 'temperature niches', were isolated from the fluctuating chemostat compared to only one group isolated from the stable chemostat. Furthermore, a pseudomonad from the fluctuating chemostat was shown to out-compete another pseudomonad from the stable chemostat when both were subjected to the fluctuating temperature regime. However, the pseudomonad of constant (8°C) temperature origin out-competed that isolated under fluctuating conditions when subjected to a stable temperature regime.     

Gene expression during CAM induction under salt stress in Mesembryanthemum: cDNA library and increased levels of mRNA for phosphoenolpyruvate carboxylase and pyruvate orthosphosphate dikinase

Mesembryanthemum crystallinum responds to high salinity in the soil by shifting the mode of carbon assimilation from the C3 mode to Crassulacean acid metabolism (CAM). Several enzymes of carbon metabolism have increased apparent activities in the CAM mode, including phosphoenolpyruvate carboxylase (PEPcase) and pyruvate orthophosphate dikinase (PPDK). We have identified cDNA clones for PEPcase and PPDK by immunological screening of a cDNA library constructed in the protein expression vector lambda gt11. The clones were characterized by immunoblotting and RNA blotting techniques. RNA blotting showed that during CAM induction the steady-state level of mRNAs for both PEP case and PPDK increased.Abbreviations IPTG isopropyl thiogalactoside - PEP phosphoenolpyruvate - PEPcase phosphoenolpyruvate carboxylase - PPDK pyruvate orthophosphate dikinase - Xgal-5 bromo-4-chloro-3-indolyl-beta-D-galactopyranoside     

Effect of Within-field Variation in Soil Texture on Heterodera glycines and Soybean Yield

The influence of soil texture on Soybean yield in the presence of Heterodera glycines was investigated by comparing yields of susceptible cultivars with a resistant cultivar for 2 years. Soybean yield was negatively correlated with increasing sand content (P = 0.05). Yields of susceptible cultivars were suppressed with increasing sand content. Final nematode population densities were lowest in plots with greatest sand content. Soybean infection by SCN, as determined by the number of cysts 30 days after planting, was not consistently related to soil texture over 2 years. Initial nematode population density was positively related to soybean yield the first year and negatively related to soybean yield the second, probably a result of greater yield suppression by H. glycines in plots with greater sand content.     

Influence of pH,exchangeable aluminium and 0.02M CaCl2-extractable aluminium on the growth and nitrogen-fixing activity of white clover (Trifolium repens) in some New Zealand soils

The effects of soil acidity on the growth and N₂-fixing activity of white clover in seven acid topsoils and subsoils of New Zealand were investigated using a glasshouse experiment.The application of phosphate (Ca(H₂PO₄)₂) to the soils resulted in very large increases in white clover growth on all soils. The application of phosphate, as well as increasing P supply, also decreased 0.02M CaCl₂-extractable Al levels, but had little effect on exchangeable Al levels.Where adequate phosphate was applied, increasing rates of lime (CaCO₃) resulted in increased plant growth on most soils. N₂[C₂H₂]-fixing activity was increased by the first level of lime for one soil, but generally remained approximately constant or declined slightly at higher rates of lime. Up to the point of maximum yield, white clover top weight was more highly correlated with 0.02M CaCl₂-extractable soil Al than with exchangeable Al or pH. At pH values greater than 5.5, plant yield declined on some soils, apparently because of Zn deficiency. The data suggest that white clover is unlikely to be affected by Al toxicity at 0.02M CaCl₂-extractable Al levels of less than about 3.3 g g^–1. However, there were differences between soils in apparent plant tolerance to 0.02M CaCl₂-extractable Al, which appeared to be caused by differing C levels in the 0.02M CaCl₂ extracts.     

Yield and nitrogen uptake of rapessed (Brassica campestris L.) with ammonium and nitrate

Water culture, growth chamber, greenhouse and field experiments were conducted to compare the effect of NH₄−N and NO₃−N on yield and N uptake of rapeseed (Brassica campestris L.). In water culture, the yields of 28-day old rapeseed plants grown at 14 μg N ml⁻¹ were double with NO₃ compared to NH₄, but N uptake was little affected. There was no such effect when concentration was reduced to 3.5 or 7 μg N ml⁻¹. The yield and N uptake of 26-day old rapeseed grown on six soils (pH 4.6 to 6.5) in pots in a growth chamber were much greater with NO₃ than with NH₄, although N concentration was more in the NH₄- than the NO₃-grown plants. In a greenhouse experiment with rapeseed grown on 12 potted soils, the N uptake of applied N was greater with NO₃ than with NH₄ on all soils. Averages were 63% with NH₄ and 78% with NO₃. However, NH₄-fixation capacities of the soils were only weakly correlated with yield from the two sources of N (r=0.48) and the relation was similar with N uptake. In contrast to the behavior of water culture, growth chamber and greenhouse experiments, the 33 field experiments did not show consistent difference in seed yield with NH₄ and NO₃ applied at time of seeding. In nine field experiments where band application was used for Ca(NO₃)₂, (NH₄)₂ SO₄, NH₄ NO₃, yield tended to be greatest for (NH₄)₂SO₄. However, in 19 experiments on acid soils with and without lime, yields in most cases were similar with (NH₄)₂SO₄ and NH₄ NO₃. Nitrification inhibitors were added to spring banded NH₄-based fertilizers in five experiments, but the yields were not influenced. Scientific Paper No. 558, Lacombe Research Station, Agriculture Canada.     

Growth and development of maxipak wheat as affected by soil salinity and moisture levels

The effect of soil salinity and soil moisture on the growth and yield of maxipak wheat (Triticum aestivum L.) was studied in a lath-house experiment in whih, chloride-sulphate salt mixtures were used to artificially salinize a sandy loam soil from Al-Jadyriah Baghdad. Five soil salinity levels of ECe's equal to 1.7 (Control) 4.2, 5.8, 8.1, 9.4 and 11.0dSm^–1 were prepared and used at 3 levels of available soil moisture depletion, namely, 25, 50, and 75% as determined by weight. Both growth (vegetative) and yield components were studied throughout the growing season.Results showed that increasing the soil salinity from 1.7 to 11.0 dSm^–1, and decreasing the available soil water from 75 to 25% resulted in independent and significant decreases in Mazipak wheat growth and yield components at different stages of plant development. Root growth showed more sensitivity to both available soil water and soil salinity level than other components. It has been concluded that at soil salinity levels of more than 8.0 dSm^–1, available soil water became a limiting factor on wheat growth and the maintenance of 75% of available soil water during the growth period is recommended to obtain satisfactory grain yield.     

The profile distribution of total and extractable boron in cacao-growing soils in southwestern Nigeria

The profile distribution of total and extractable B was determined in 16 Nigerian cacao-growing soil profiles formed from different parent materials. Total B for all soils ranged from 8 to 54μgg⁻¹ with a mean of 24μgg⁻¹. The soils formed from sandstones in the rainforest zone contained higher amounts of total B than soils derived from basement complex. Boron extractable in hot water, in 0.1% CaCl₂, and in 1N NH₄OAc varied from 0.13 to 1.38, 0.44 to 1.20 0.03 to 0.56μgg⁻¹ respectively. The corresponding means were 0.66, 0.75 and 0.27μgg⁻¹ B. Soils on metamorphic rocks gave the highest values. All extractable B values were related to organic matter while only CaCl₂-extractable B correlated with total B. Generally total and extractable B values were higher in the top soils than in the subsoils.     

Size dependency of gametophytes decay inAthyrium brevifrons Nakai during spring desiccation

Gametophyte populations inAthyrium brevifrons were analysed with respect to population size and surviving area (%) of individual thalli in a transplant garden at Sapporo during 5–26 April 1983, to study the safe-microsite for gametophyte establishment in nature. Spores dispersed in August 1982 germinated and grew into thalli of various widths (<10 mm); 10.3% of the thalli matured by early October 1982. Maturation was attained by gametophytes of width 4–7 mm. The number of gametophytes gradually decreased with increasing width. By April 1983, 20.5% of total gametophytes were mature with a mode of 5–6 mm in width. The relative number of gametophytes with surviving area of 2–20% increased and that of 85–100% decreased in accordance with collection days delayed until after snow-melt. Surviving area (%) on gametophyte of all widths decreased with decreasing soil moisture contents. In particular, immature gametophytes of 2–4 mm width showed a significant correlation (P<0.01) between soil moisture content and relative number of gametophytes with 0–20% surviving area and mean surviving area (%) of every width of thalli. The spring desiccation might be a factor that reduces or limits gametophyte populations in nature.