Trends in wheat yields and soil organic carbon in the Permanent Rotation Trial at the Waite Agricultural Research Institute, South Australia

The Permanent Rotation Trial at the Waite Agricultural Research Institute in South Australia was established on a red-brown earth in 1925, with predominately cereal-long fallow rotations on 34 adjacent plots. The trial was upgraded in 1948 to include a greater proportion of pasture leys in the rotations and currently contains 11 treatments. The trial is unreplicated; however, each phase of a sequence is represented each year. Seven of the original rotations have remained in an unbroken sequence since 1925: continuous wheat (W), wheat-fallow (WF), wheat-peas (WPe), wheat-pasture-fallow (WPaF), wheatoats- fallow (WOF), wheat-barley-peas (WBPe), wheat-oats-pasture-fallow (WOPaF). For the 11 rotations, soil organic carbon (SOC) in the top 10 cm declined from 2.75% in 1925 to a mean value of 1.56% in 1993. One plot, which had reverted to permanent pasture in 1950, showed the smallest decline with an SOC content of 2.46% in 1993. The greatest declines in SOC were in the 4 original rotations that included fallow phases in the sequence (mean value of 1.22%). In the WF rotation the SOC content had declined from 2.75 to 1.04% during 68 years of cropping. Associated yield decreases showed that the treatment could not sustain production. Soil organic C declined linearly with increasing frequency of fallows and decreasing frequency of pasture in the rotations. Average grain yields (1925-93) in the 7 original sequences ranged from 2.64 t/ha in WOPaF to 0.89 t/ha in the continuous W plot. The linear decline in yields for WBPe, WPaF, WPe, and WOF treatments indicate a convergence in the 1990s under current management, with an average yield of 1.54 t/ha in 1993 and average SOC in the top 10 cm of 1.32%. We hypothesise that the gradual increase in grain yields from the continuous W plot since the 1960s is the result of a gradual build-up of light fraction organic material, which assists in the maintainence of structure and nutrient availability.

Structural amelioration of a South Australian red-brown earth using calcium and organic amendments

The ability of wheat straw, gypsum and agricultural lime to ameliorate the unstable structural condition of a degraded red-brown earth located at the Waite Agricultural Research Institute, South Australia, was investigated in a field experiment lasting 5 years. Wheat straw was added at rates of 0, 5 and 10 t ha-1 y-1, and gypsum and agricultural lime were added at rates of 3.4 and 2.0 t ha-1 y-1 respectively. Most of the measurements were taken on samples collected after three and four consecutive years of treatment applications, but some were taken one year after the fifth and final application of the treatments. The amount of water-stable macroaggregation in the top 10 cm increased with increasing rate of wheat straw application. Addition of agricultural lime incorporated with straw temporarily increased macroaggregate stability to a greater extent than was observed with either amendment alone. The proportion of the soil surface occupied by macropores was also increased significantly by addition of agricultural lime, and this was attributed to a stimulation of biological activity in the soil due to the increased soil pH. Density fractionation of the soil suggested the turnover of the added wheat straw in the lime-treated soil was greater than in the gypsum-treated and control soils. Addition of gypsum decreased the content of mechanically dispersible clay by modifying the electrolyte concentration and composition, but was unable to completely resist the dispersive tendencies created by the decomposing organic residues. The high rates of wheat straw incorporated in the top 10 cm caused significant dispersion in the top 20 cm, which was thought to have mobilized clay particles causing them to move downward, resulting in pore blockage and the consequent lowering of hydraulic conductivity in the zone immediately below.

The growth and yield of uniculm and tillered barley over a range of sowing rates

The growth and yield of two lines of uniculm barley, WID-103 and WID-105, were compared over a range of sowing rates (50-400 kg/ha) with the commercial varieties Galleon and Schooner. The experiments were conducted at Strathalbyn, S.A., in 1986, 1987 and 1988 and at the Waite Agricultural Research Institute in 1987. A third tillered variety, Clipper, was included in the comparison in 1988. Over the three years plant populations measured early in the season ranged from 39/m2 to 709/m2, and grain yields from 97 to 41 1 g/m2. Dry matter production at ear emergence increased with greater plant density, and both the tillered varieties and the uniculm lines showed similar responses to higher sowing rates. At maturity, dry matter production of the tillered barleys was greater than or equal to that of the uniculms and the harvest indices (HIs) of the two types were similar. Consequently, grain yields of the tillered types were greater than or equal to the yields of the uniculms. Over the four experiments the tillered varieties had a 6% higher yield. The number of ears/m2 was the yield component most affected by plant density in both the tillered and uniculm barleys. The uniculm lines had more spikelets/ear, but tended to set fewer grains/spikelet and produce smaller kernels. The experiments failed to demonstrate any advantage of the uniculm habit to the grain yield of barley. These results differ from previous experiments that showed that a uniculm line, WID-101, had a higher yield than the tillered variety Clipper. It is suggested that the uniculm habit per se was not the cause of this higher yield, but its higher HI resulted in it outyielding Clipper. Current varieties, however, have HIs similar to the uniculm lines and yield equally to or more than the uniculm barleys examined. To further improve the grain yield of uniculm barley, greater dry matter production is necessary as the HIs of these lines are already high.

The Movement of Fluids and Substances in the Testis

Department of Animal Sciences, Waite Agricultural Research Institute, University of Adelaide, Glen Osmond, S.A. 5064