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Cereal grain yield response to pasture legume nitrogen

C.K. Revell

WA Department of Agriculture, Dryland Research Institute, PO Box 432, Merredin WA 6415

Pasture legume leys can contribute substantially to nitrogen (N) nutrition of cereal crops when grown in rotation. Burr medic, Medicago polymorpha L., in association with new strains of Rhizobium meliloti, has been shown to be well adapted to mildly acidic (pH 1:5 H20 > 6.0), medium textured soils in the 250-450 mm annual average rainfall zone of the Western Australian wheatbelt (1). Little information has been documented on the performance of burr medic in cereal-ley rotations or its value to subsequent cereal crops. This paper describes some selected results from a long-term rotation trial established near Merredin, WA.


Pastures were sown to burr medic cv. Santiago in 1988 and produced 5 t/ha dry matter. Cereal rotations commenced in 1989. In 1990, wheat grain yields from several histories were contrasted for continuous crop with varying rates of ammonium nitrate fertiliser (34% N) applied at seeding, first crop after two years pasture and second crop after one year pasture. Crops were sown to wheat cv. Spear on 15 May 1990 following a cultivation in March and April. Crops in cereal (C)/pasture (P) rotations were grown without added N fertiliser.

Results and discussion

In the continuous crop treatment, tiller number, dry matter (DM) at anthesis and grain yield showed a quadratic response to applied N. Maximum response was obtained at 40 kg N/ha. Grain protein on the other hand responded in a linear fashion, at a rate of 0.057%/kg N (or 17.5 kg N/ha for every 1% increase in protein). Grain yields in both cereal/pasture treatments were similar and were equivalent to continuous crop treatments receiving 20-40 kg N/ha. Grain protein levels, differed substantially and reflected the stage of rotation. First crop treatments had a protein level equivalent to continuous crop treatments receiving 50 kg N/ha, while second crop treatments showed a protein level equivalent to 20 kg N/ha. Comparative measurements of grain protein, in combination with grain yield, will provide a more accurate means of estimating the amount of legume N suppled to cereal crops.


This project is funded by the State Wheat Industry Research Committee of WA.


Howieson, J.G. and Ewing, M.A. 1986. Aust. J. Agric. Res. 37, 55-64.

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