Four adsorption equations were fitted to phosphate isotherm data for 38 soils from northern New South Wales. The two-surface Langmuir equation provided the best fit to the data. The Freundlich equation, however, was almost as effective, provided that an estimate of native adsorbed phosphate was included. It required fewer adsorption points because the transformed data produced a straight line. A regression constant, a, from the Freundlich equation although underestimating adsorption capacity, calculated from the Langmuir II equation, was highly correlated with this parameter (r = 0.984) and a buffering index (r = 0.986), calculated from the Langmuir I equation. The other Freundlich regression constant, n, was significantly correlated (P <1%) with the intensive parameters of adsorption from the one- and two-surface Langmuir equations. Since only two adsorption points are required for fitting the Freundlich equation and the parameters are easier to derive, it is suggested that this equation may be more suitable for commercial soil-testing laboratories than the Langmuir one- and two-surface equations for routine determination of phosphate adsorption characteristics of soils.

The infiltration behaviour and physical properties of a hardsetting sandy loam soil at Cowra, N.S.W., following 2 years of different tillage treatments are reported. Soil that had not been cultivated for 25 years was also investigated at an adjacent pasture site. Infiltration of simulated rainfall at the end of the wheat-growing season gave moisture profiles that were quite different for cultivated, direct drilled and pasture soils. The moisture profile for the cultivated soil suggested the presence of an impeded layer which retarded the movement of infiltrated rain to the subsoil. Porosity measurements confirmed the presence of a layer with significantly fewer macropores (> 300 �m diameter) at the 50-100 mm depth in the cultivated soil, when compared with the direct drilled soil. The old pasture soil had significantly higher porosity (> 300 �m diameter) in the top 100 mm. Aggregate stabilities and organic carbon contents were measured in narrow increments to 150 mm depth for the three different soils, and revealed that a surface 25 mm layer of high organic carbon and highly stable macro-aggregates was present in the pasture and direct drilled soils but absent in the cultivated soil. The unstable surface layer in the conventionally cultivated soil was a consequence of the mixing and inverting action of cultivation and was not due to a net loss of organic carbon from the profile. The organic carbon content of the pasture soil was not significantly different from the direct drilled soil below 50 mm; however, it was significantly lower than the conventionally cultivated soil between 50 and 150 mm depth. These results indicate a need to adopt tillage practices that can preserve the top 25 mm layer of such fragile soils.

Land preparation for canola (oilseed rape; Brassica napus L.) by conventional cultivation can involve a number of workings, resulting in soil degradation and reduced crop growth. Minimum-tillage systems may help overcome these problems, but the placement of fertiliser at sowing must avoid chemical injury to germinating seed. The responses of canola cultivars to tillage and fertiliser placement were studied for 2 seasons at high (Breakfast Creek, 1997; Harden, 1998) and low (Ardlethan, 1997–98) rainfall sites. The tillage treatments were conventional cultivation, one-pass, and no-till (direct drill). The fertiliser treatments were 200 kg/ha 'starter' fertiliser (a�compound fertiliser supplying 30 kg N, 26 kg P and 22 kg S/ha) either placed with the seed, or broadcast, or banded to the side and 3 cm below the seed. In 1997 the canola was sown after wheat, and in 1998 after pasture. Plant establishment of all cultivars was reduced by 40–65% when fertiliser was placed with the seed; tillage treatment did not alter this response. Placing fertiliser with the seed reduced dry matter/m2 by up to 40% in plants at flowering, but by physiological maturity, there were no differences in dry matter/m2 due to fertiliser placement. Analysis of the combined seed yields for both years showed that although plants in the with-seed placement compensated by producing more seed/plant, this compensation was sufficient only at Breakfast Creek for yields to be comparable to those of the other fertiliser placements. Tillage had little effect on seed yields. In 1997, no-till yielded more than one-pass at Ardlethan, but in 1998 at Ardlethan no-till yielded less than the other tillage systems. Fertiliser placement and tillage had no effect on seed oil concentration and meal protein content. Cone penetrometer measurements (1998) showed no differences in soil strength between tillage treatments at Ardlethan; while at Harden, one-pass had less soil strength than the other tillage treatments. Crop water extraction was not affected by tillage at any site. It is concluded that a conservation-farming system involving no-till or one-pass tillage, and separation of seed and fertiliser has the potential for producing high yielding canola crops, reducing the risk of soil degradation, as well as saving time and land-preparation costs.

Cold tolerant isolates of Gaeumannomyces graminis var. graminis (Ggg) and Phialophora sp. (lobed hyphopodia), which produced at least comparable growth rates at 58C to those of pathogenic G. graminis var. tritici (Ggt), were shown to control take-all disease in wheat effectively in 2 years of field experiments in New South Wales, Australia. The addition of oat inoculum of these fungi at the rate of 60 kg/ha to the seeding furrow significantly (P 4 0 . 05) reduced disease and increased grain yields by 33-45% compared to the Ggt alone treatment. The use of 30 kg/ha of oat inoculum also significantly (P 4 0 . 05) reduced disease and increased grain yields by 21-44%. These high levels of take-all control were obtained consistently from four field experiments on three different soil types with different pHs. A treatment inoculated with Ggg alone showed no disease symptoms and produced grain yields similar to that of untreated wheat. This fungus is, therefore, non-pathogenic to wheat. At high rates of inoculation of Ggg and Phialophora sp. (lobed hyphopodia), 65-80% of tillering wheat plants (GS 32) had root systems colonized by these fungi. In contrast, two Pseudomonas spp. and an isolate each of Ggg and Phialophora sp. (lobed hyphopodia), which did not grow at 58C, were ineffective in controlling take-all. Take-all assessments during heading (GS 61-83) were highly correlated (R 2 =0 . 6047, P40 . 0005) with the relative yield increase or decrease of inoculated treatments compared to the Ggt alone treatment. The use of a Ggg isolate (90/3B) and a Phialophora sp. (lobed hyphopodia) isolate (KY) for take-all control has been patented. These fungi are being developed for commercial use.

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