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Predicting the emergence of annual pasture legumes on cereal farms

E.D. Carter and R.G. Porter

Department of Plant Science, Waite Agricultural Research Institute, The University of Adelaide, Glen Osmond SA 5064

Soil core sampling of a stubble paddock in autumn can be utilized to determine the total seed reserves of annual pasture legumes, which can provide an indication of potential density of regenerating clover or medic following opening rains (1). A more accurate estimate can be made by employing methods to determine the soft seed component of the total seed reserve, which can then be used as a guide when assessing pasture renovation requirements (2). Two techniques available to farmers for estimating potential clover or medic emergence are described in this paper.


Potential emergence of clovers and annual medics regenerating in stubble paddocks following a cereal crop was estimated using two techniques in the period 4 March to 24 April 1991, in the cereal districts of Eyre Region and Central Region. The techniques used were as follows: (i) germination/emergence (plants/m2) of medic, subterranean clover and balansa clover in situ in stubble paddocks following application of water to steel rings; and (ii) germination/emergence (plants/m2) of medic and subterranean clover from soil core samples in containers.

In the first method, steel cylinders (diam. 284 mm) were driven into the soil to a depth of approximately 50 mm. Five litres of water were initially added to the cylinders, with subsequent waterings of two litres every two days to ensure complete and rapid emergence of readily germinable seed. The cylinders were covered with a white polypropylene bag to inhibit evaporation and prevent interference by grazing animals. In the second method, 4 core samples (100 mm diam. x 50 mm deep) were taken in close proximity to the steel cylinders. Half of these cores were transferred to pots and watered to field capacity to allow germination and emergence, simulating the procedure of a commercialised pasture legume seed soil test kit from Agchem Pty Ltd. The remaining cores were sieved (0.5 mm for balansa clover, 0.7 mm for medics and 1.0 mm sieve for subterranean clovers) to determine total seed reserves, and the sieved soil used for nitrogen analyses. Soil core samples were collected and transported from stubble paddocks to the Waite Institute. Additional soil core samples were sieved to determine the total seed reserve of sampled paddocks.

Results and discussion

Table 1. Regression equations showing inter-relations of seed reserves, pot emergence (PR), ring emergence following watering (AR), natural regeneration (NR) of annual legumes, and percentage nitrogen content (N) of the soil.

Data show clearly that in situ ring emergence gives a good prediction of natural regeneration. Usefulness of using legume seed reserves as an indicator of soil N percentage looks promising but needs further development.


Carter, E.D. 1982. 2nd Aust. Agronomy Conf., Wagga Wagga. p. 180.

Carter, E.D., Le Leu, K.M. and Baldwin, G.B., 1989. 5th Aust. Agron. Conf., Perth. p. 438.

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