Rapid methods for measuring the severity of water repellence were assessed in 101 sandy soils from South Australia. The molarity of aqueous ethanol droplets that were absorbed by the soil in 10 s, the time of water droplet entry and the infiltration rate of water from a small ring infiltrometer were compared with the soil-water contact angle and with each other. Relationships between the tests were fitted by linear, quadratic and cubic regressions and were highly significant (100r2 = 70-92). The relationships were used to provide ratings of repellence normally found in the field.Factors which affect the measurement of repellence in the field were examined. Abrasion of sand particles during light sieving had only small effects on repellence, but more vigorous abrasion through rotational movement of the sand reduced repellence markedly. Repellence decreased with increasing temperature. Simple corrections for temperature were calculated and presented in figures as isorating charts.The moisture content of the soil had large and variable effects on the repellence tests. At moisture contents between oven and air dry (pF 5.6) there was little effect on the ethanol droplet or infiltration rate tests. Measurements by the ethanol droplet test were not reliable at moisture contents greater than air dry. At soil water contents between air dry and wilting point (pF 4.2), the infiltration rate of water was either unchanged or decreased in different soils. It then increased rapidly and reached a constant value near field capacity (pF 2.5). The infiltration rate also decreased when the time of moistening of the soil before the tests were made was extended from 20 to 168 h. It is recommended that repellence tests be made on oven-or air-dry soils. The aqueous ethanol and water droplet, and infiltration rate of water tests are all suitable for rapid assessment of repellence in the field.

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Response of vegetative growth and grain yield of wheat Triticum aestivum cv. Condor to the control of cereal cyst nematode Heterodera avenae by nematicides applied with the seed, in the drill row was assessed in twenty field trials. These trials were conducted in 1978 on three soil types near Coonalpyn, South Australia. Aldicarb was used at all sites and fosthietan and terbufos at four sites. Significant grain yield increases to aldicarb were obtained at 12 sites while yields were increased by the three nematicides at three sites. Numbers of eggs of H. avenae were determined in soil taken in January 1978, and these counts showed that all sites were infested over the range 0.03-8.5 eggs/g soil. Plant assays of the soils assessed the reduction in the length of seminal root axes (range 0-45%) and the severity of the root knotting caused by H. avenae. The egg densities in the soil, reduction in the length of the seminal root axes and disease ratings in the plant assay were highly correlated with each other (r = 0.75; P< 0.001 to 0.91, P< 0.001). These variables were not significantly correlated with grain yield increase due to aldicarb on the two major wheat soils studied, although a correlation, explaining 32-42% of the increase, existed when all sites were considered. A mathematical model based on cropping history and an estimated annual hatch of eggs of H. avenae failed to show a relation between these variables and the yield increase from nematicide. H. avenae caused severe disease and yield loss on calcareous loams and red duplex soils but had only minimal effects at the sites on siliceous sands.

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A crop rotation experiment was conducted at Coonalpyn, South Australia from 1976 to 1979 on a deep, red duplex soil. The experiment compared the productivity of grain legumes and of volunteer and sown annual pastures, and assessed their effects on the mineral nitrogen supply for subsequent wheat and barley crops, and their capabilities for preventing the root diseases of wheat cereal cyst nematode (Heterodera avenae), bare patch (Rhizoctonia solani) and Haydie (Gaeumannomyces graminis). Satisfactory legume dominance of the annual pastures was achieved only in 1979, while the grain legumes grew well and produced more dry matter than the pastures in each season. Wheat and barley yields averaged (1977- 1979) 2.0 t/ha after volunteer and sown pastures, and 2.8 t/ha after grain legumes, with the greatest response in 1979. In that year, wheat produced 11 kg grain/mm of growing season rainfall after grain legumes, but only 6 kg after pastures. The numbers of lesions on the nodal roots caused by R. solani and on the seminal roots by G. graminis varied with the season but both were less after grain legumes than after pasture. Gaeumannomyces graminis had the greatest effect on grain yield and, with soil nitrate at seeding, explained up to 68% of the variation in yield in 1979.