Seed size matters in depth of seeding when growing

Seed size matters in depth of seeding when growing yellow lupins. Leigh Smith and Kedar Adhikari, Department of Agriculture and Food BACKGROUND Yellow lupins (L. luteus) are being researched as a higher protein lupin with excellent market prospects for aquaculture. Early research into the establishment of yellow lupins suggests that they do not emerge as successfully from depth as narrow-leafed lupins (NLL). A recent depth of seeding trial (Smith and Sweetingham 2007) supports this observation however it didn’t investigate if seed size was a factor in depth of seeding and emergence. Generally the yellow lupins have smaller seed compared to NLL. However, there are several lines within the yellow lupin breeding program that are equivalent to or larger in seed size than some NLL varieties.

AIMS To determine the effect of seed size and depth of seeding on the time of emergence and early plant vigour in yellow lupins.

METHOD Five yellow lupin, two narrow-leafed lupin and one wheat genotype with different seed size were used in the study (Table 1). The seeds were planted at three depths of seeding (1, 5 and 8 cm) in three fully randomized replicates. The wheat was used as a comparison to see if their smaller coleoptile made any difference in the rate of emergence compared to the larger cotyledon of lupins. The experiment was conducted in a glasshouse using 150 mm x 160 mm plastic pots filled with an equal amount of loamy soil and washed river sand with eight seeds per pot were sown at measured depths. No nutrients were added to the soil and the pots were watered to saturation. Emergence counts were nd carried out at 7, 11, 18 and 22 days after seeding. On 22 day after seeding all plants were cut to take a dry matter weight (biomass production (g)/pot) and biomass was calculated per plant (g/plant).

RESULTS Emergence Merrit at 1cm was the first to emerge on the fourth day. By day seven, there was 75% emergence on most of the lines sown at 1 cm. There was no emergence from other depths at this time except for the 60% of NLL at the 4 cm depth. On day eight 54 - 96% of all lines had emerged from 4 cm. However, the yellow lupin lines were only just breaking the surface at this depth. 94D019-3-6, the smallest seed size, yellow lupin had the best establishment within the yellow lupin group. It was 29% better than Wodjil and 19% better than the largest seeded yellow 96D004-4-9. 94D019-3-6 was equivalent in plant number to Merrit at both the 1 cm and 4 cm depth. At day eight nearly all lines had reached 100% emergence except for 96D004-4-9 at the 1 cm depth. Its bigger seed and thicker seed coat might have taken longer to imbibe. There was still no emergence from 7 cm depth and Wyalkatchem had only its coleoptile showing. By day nine, the two NLL lines started to emerge from 7 cm depth. Maximum emergence was reached by day nine of the varieties buried at 1 and 4 cm. On the eleventh day, 94D019-3-6 was showing faster emergence than the other yellow lupin lines at 7 cm depth. It had 43% better germination than Merrit from this depth.

All lines had reached maximum emergence eighteen days after sowing. As expected the depth of seeding was significantly different (P < 0.001, 5% lsd = 0.628) with establishment decreasing as depth increased. There was a reduction in establishment of up to 22% from 1 cm to 7 cm depth. But the larger seeded 96D004-4-9 was not affected. The smaller seeded lines were most impeded by greater depth. Table 1:

Various lupin species along with Wyalkatchem, a wheat genotype, and their seed size (100 seed weight g) used in the depth of seeding trial in glasshouse conditions at South Perth. Number of plants established at 18 days after seeding at different sowing depths

Species

Variety

100 seed weight (g)

Depth cm 1

4

7

3.7

7.7

7.3

4.3

10.5

8.0

8.0

6.3

11.1

7.7

7.3

6.7

Pootallong

12.1

8.0

5.7

5.3

L. luteus

94D016-7-9

12.8

8.0

7.3

5.0

L. angustifolius

Merrit

13.3

7.7

7.0

6.0

L. luteus

96D004-4-9

14.6

6.7

6.7

6.7

L. angustifolius

Coromup

16.2

8.0

7.7

8.0

T.aestivum

Wyalkatchem

L. luteus

94D019-3-6

L. luteus

Wodjil

L. luteus

Seedling biomass Although, Wyalkatchem had a reduction of 56% plant establishment between 1 cm – 7 cm (7.67 – 4.33 plants), there was only a 16% reduction in biomass. The analysis of biomass showed that variety and depth of seeding were significant (P < 0.001), but their interaction was not significant (P = 0.1605). The overall loss of dry shoot weight was 58% from 1 cm to 7cm depth of seeding. All genotypes suffered a loss in dry matter. There was more loss from 4 cm to 7 cm (25% to 70%) depths than 1 cm to 4 cm (1% to 30%). 1.6 1.4

Dry shoot weight (g/pot)

1.2 1 0.8 0.6 0.4 0.2

Coromup 96D004-4-9 Merrit 94D016-7-9 Pootalong Wodjil 94D019-3-6

0 1cm

4cm

7cm

Depth of seeding cm

Figure1:

The dry shoot weight (g/pot) from various lupin genotypes at different seeding depths at 22 days after seeding.

Although 96D004-4-9 had poorer plant establishment than Wodjil, its plant number was the same for all depths. Its dry shoot weight was up to 122% better than Wodjil, and outperformed Pootallong by 111% to 177% depending on the depth of seeding. This indicates that larger seed size of 96D004-4-9 contributed to bigger biomass production.

The smallest seed size (94D019-3-6) had a reduction in dry shoot weight for its relevant depth of seeding. However it was 103% to 142% better compared to Pootallong for their relevant depths, but it was not significantly different from the other four yellow lupin genotype.

CONCLUSION Seed size can influence emergence and seedling vigour. Emergence of larger seed genotypes was not affected by deeper sowing up to 7 cm, but the smaller seeded genotypes were reduced. These results suggest that seed size should be a consideration for breeding yellow lupins as growers have repeatedly had problems with plant establishment.

KEY WORDS L.luteus, L.angustifolius, depth of seeding, seed size, emergence

REFERENCES Smith L. and Sweetingham M. (2007) Effects of sowing depth on the emergence and vigour of different lupin species. Agribusiness Crop Update 2007, Lupin & Pulses section Project No.:

DAW104

Paper reviewed by:

Mark Sweetingham