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Comparative productivity of oilseeds and cereals

J.F. Angus and A.F. van Herwaarden

CSIRO Division of Plant Industry, Canberra, A.C.T., 2601

The only oilseed grown in significant quantity in southern Australia is canola. It is concentrated on the wetter fringe of the wheatbelt and expresses its potential only when sown early. Linseed and mustard may be adapted to growing in other regions and to later sowing but their oils are in low demand. Breeding programmes in the CSIRO Division of Plant Industry have led to development of a low linolenic acid linseed and a low erucic acid mustard. The productivities of linseed and mustard were compared with those of canola, wheat and oats at Barellan in the NSW Riverina.

Methods

The site was a red-brown earth on which a clover-based pasture had grown for the previous four years. The only known nutrient deficiency at the site, P, was overcome with superphosphate at the rate of 15kg P ha-1. The experiment was sown on 1/6/88. Measurements were made on soil water, light interception (on 28/9/88), seed and straw nitrogen, and oil content of seed. Productivity was calculated not only in terms of mass but also as primary productivity expressed as the glucose required to produce the above-ground tissue (1).

Results and discussion

The Table shows that wheat was the most successful crop in terms of yield, biomass, primary productivity and nitrogen uptake. The inferiority of oats was partly due to crown rust and barley yellow dwarf virus, but there were no apparent biotic limitations to the oilseeds. The low yields of canola and linseed were associated with low primary productivity rather than allocation of assimilates, as shown by the harvest index expressed on an energy basis. The primary productivity of mustard was greater than the other oilseeds but its harvest indices, based on both mass and energy, were relatively low. The crops used similar amounts of water, although linseed extracted less water at soil depths below 80 cm than the other crops. It is likely that the oilseeds, because of their poorer canopy cover, lost more water as soil evaporation than the cereals. Measurements during spring confirmed that the topsoil under the oilseeds was drier than under the cereals. Dry topsoil may have restricted nitrogen uptake by the oilseeds. The results, although confined to a single experiment, point to the need for research to increase the canopy cover in the oilseeds.

1. Penning de Vries, F.W.T. 1974. Neth. J. Agric. Sc. 22, 40-44. 525

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