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Effects of depth of sowing medic seeds on emergence of seedlings

E.D. Carter and S. Challis

Agronomy Department, Waite Agricultural Research Institute The University of Adelaide, Glen Osmond, South Australia 5064

Tillage for cereal crops in wheat belt rotations buries clover and medic seeds produced in the pasture years. Observations suggest that deep burial of seed in the tillage program and lack of precision in depth of sowing cause low densities of pasture legumes both in Australia and overseas (1). This paper summarizes data on emergence of four medic species from three depths of sowing in sand and loam.

Methods

Seeds of Medicago scutellata cv. Robinson, M. rugosa cv. Paragosa, M. truncatula cv. Jemalong and M. littoralis cv. Harbinger were each sieved to give three seed sizes. Surface soil (0-15cm) of mallee sand from near Mallala and a red brown earth loam from the Waite Institute were sieved to remove debris and weighed into 15cm square, black plastic, free-draining pots which were located in a glasshouse. Twenty five seeds per pot were shown at 1,3 or 5cm depth and watered with rainwater. There were six replicates. After 14 days the plants were harvested.

Results and Discussion

Table 1. Percentage emergence+ and seedling dry weight of four medic species sown at three depths in both sand and loam. (Mean of three seed sizes.)

As depth of sowing increased, emergence and seedling dry weight decreased: this was more obvious in the loam than the sand (Table 1). Emergence from the large seeds was less than that from seeds of medium size at 1cm and 3cm depth, especially in the loam (Table 2).

Table 2. Percentage emergence+ from different seed sizes. (Mean of 4 species.)

This research has shown that emergence of medic seedlingsranges from 99% to 0% depending on cultivar, seed size, depth of sowing and soil texture. It highlights the need to avoid deep burial of medic seed by ploughing (2) and to avoid sowing the smaller-seeded medics below 1cm in loans.

1. Carter, E.D. 1974. A report prepared for CIMMYT, Mexico, and MARA, Algeria. Waite Agric. Res.Inst., South Aust. 54p. plus appendices.

2. Quigley, P.E., Carter,E.D. and Knowles, R.C. 1987. Proc.4th Aust.Agron.Conf., Melbourne.pp.

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