Growth and elemental accumulation by canola on soil amended with coal fly ash

To explore the agronomic potential of an Australian coal fly ash, we conducted two glasshouse experiments in which we measured chlorophyll fluorescence, CO2 assimilation (A), transpiration, stomatal conductance, biomass accumulation, seed yield, and elemental uptake for canola (Brassica napus) grown on soil amended with an alkaline fly ash. In Experiment 1, application of up to 25 Mg/ha of fly ash increased A and plant weight early in the season before flowering and seed yield by up to 21%. However, at larger rates of ash application A, plant growth, chlorophyll concentration, and yield were all reduced. Increases in early vigor and seed yield were associated with enhanced uptake of phosphorus (P) by the plants treated with fly ash. Fly ash application did not influence accumulation of B, Cu, Mo, or Zn in the stems at any stage of plant growth or in the seed at harvest, except Mo concentration, which was elevated in the seed. Accumulation of these elements was mostly in the leaves, where concentrations of Cu and Mo increased with any amount of ash applied while that of B occurred only with ash applied at 625 Mg/ha. In Experiment 2, fly ash applied at 500 Mg/ha and mixed into the whole 30 cm soil core was detrimental to growth and yield of canola, compared with restricting mixing to 5 or 15 cm depth. In contrast, application of ash at 250 Mg/ha with increasing depth of mixing increased A and seed yield. We concluded that fly ash applied at not more than 25 Mg/ha and mixed into the top 10 to 15 cm of soil is sufficient to obtain yield benefits.

An exploratory evaluation of APSIM to simulate growth and yield processes for winter cereals in rotation systems in South Australia

The Agricultural Production Systems Simulator (APSIM) suite of models was used to predict dynamics in water and nitrogen in soil, as well as the growth and yield of sequential crops of wheat and barley in pasture–wheat–barley rotations, between 1995 and 1997 at Roseworthy, South Australia. The NWHEAT model satisfactorily predicted above-ground dry matter, leaf area index and grain yields for both crops in rotations with either grassy (Grass) or medic (Medic) pastures, including the lack of significant response of yield to nitrogen fertiliser applied to wheat at sowing. Simulation data for soil water, from SOILWAT2, was consistent with measured data. Simulation with SOILN2, however, largely underestimated soil nitrogen, due to excessive uptake by the simulated wheat during the season when nitrogen was abundant and water supply readily available. Thus, the soil nitrate had to be reset at sowing for the following barley crop; simulated soil nitrate agreed with the measured data in this season when this nutrient was low. For most variables of crop growth and soil water, the simulated data were mostly within 2 standard errors of the measured means. Prediction of grain protein was underestimated in all cases, including where nitrogen in the shoot was overestimated. This was possibly due to inadequate remobilisation of nitrogen from the straw and roots to the grain by the simulated crop. A satisfactory prediction of dry matter, grain yield and grain weight was obtained for wheat when the models were extended to other trials at Roseworthy (Lower North), Minnipa (Upper Eyre Peninsula) and Wunkar (Murray Mallee), based on limited soil data. Long-term simulations of wheat yields showed that, with early sowing in the Lower North, median wheat yield increased by 50 kg/ha for every kilogram of nitrogen applied at sowing, up to a maximum nitrogen rate of 50 kg/ha. In the drier districts of the Upper Eyre Peninsula and the Murray Mallee, nitrogen fertiliser of no more than 25 kg/ha, applied at sowing, was enough to achieve yield benefits in any given season. At these drier sites, crop failures occurred in 5% (Upper Eyre Peninsula) and 10% (Murray Mallee) of the seasons simulated. Median sowing dates from these simulations were 15 May for the Lower North, 30 May for the Upper Eyre Peninsula and 24 May for Murray Mallee. This suggested that sowing could be conducted at least a week earlier than currently practised in the 3 environments. This study demonstrated the capability of APSIM to predict growth and grain yield of wheat and barley, as well as the associated dynamics of soil water in the main cereal belts of South Australia.

Row spacing fails to modify soil evaporation and grain yield in spring wheat in a dry Mediterranean environment

The loss of moisture by evaporation from soil under crop canopies (Esc) has been recognized as a major cause of poor water use efficiency (WUE), and hence poor grain yield, in crops grown in environments with limited rainfall. Agronomic approaches to restrain Esc aim to reduce the transmission of solar radiation to the soil beneath the crop by improving ground cover by the crop canopy. However, the sparse canopies produced in these environments have a limited effect on evaporation during the energy dependent first stage (Es1); much of the evaporation is independent of energy at the soilsurface (Es2), and therefore less sensitive to the influence of the crop canopy. Manipulating plant arrangement, primarily by changing row spacing, may provide a simple approach for improving ground cover and restraining E,, without changing GAI, and thus improving WUE and grain yield. To explore the potential benefit of variable row spacing on Esc and grain yield in the dry (300 mm) Mediterranean environment of the eastern wheatbelt of Western Australia, spring wheat was grown in 0.09, 0.18, 0.27 and 0.36 m row spacings on coarse textured and fine textured soil types at Merredin in 1989. Esc was determined with an empirical model and measured with microlysimeters. Row spacing had no significant effect on the development of green area index (GAI), dry matter (DM) accumulation and evapotranspiration (ET) throughout the season. However, in mid-season, the proportion of ground covered by the canopy was higher and transmission of solar radiation was reduced in the 0.09 m row spacing compared with the 0.36 m row spacing. These effects did not restrain E,,, which was similar in all treatments. Esc was not restrained even when the plant density was doubled in the 0.09 m row spacing treatment. Esc during the season averaged 88 mm across all row spacings on both soils; this accounted for 56% and 48% of the mean seasonal ET on the coarse textured and fine textured soils respectively. Consequently, neither water use efficiency nor grain yield were affected by variation in row spacing; water use efficiency averaged 25 kg DM ha-1 mm-1 on both soil types. For dry Mediterranean environments of Western Australia, it was concluded on the basis of these results, and yield data from other row spacing trials in the same districts, that there are no significant yield benefits to be obtained by reducing the row spacing from the current spacing of 0.18 m.