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Seed and herbage production and cyanogenic potential of white clover cultivars under irrigation at Neuarpurr, Victoria

S.G. Clark, J. Taylor and K.F. Smith

Department of Agriculture, Pastoral Research Institute, Private Bag 105, Hamilton VIC 3300

Summary. Forty-eight cultivars of white clover, Trifolium repens, were sown at Neuarpurr, western Victoria in 1988 to determine seed production potential. Seed yields in the first year were generally low, but five cultivars gave seed yields at least equal to Haifa. Seed yields in 1989 ranged from 488-1,291 kg/ha; only eight cultivars had yields significantly lower than Haifa. In spring 1988, 27 cultivars had growth scores equal to Haifa. In winter 1989, only seven cultivars had significantly less growth (P<0.05) than Haifa. The cyanogenic potential of the cultivars ranged from 13-1,398 g HCN/g DM in September 1989; all cultivars showed reduced levels when re-sampled in November.

Introduction

White clover is the most important pasture legume in the world. International trade in seed is estimated to be in excess of 5,000 tonnes annually and is worth $13 million.

Australian production of Haifa white clover seed increased dramatically in the mid 1980s when centre-pivot irrigation was widely adopted for seed production in SA (see Fig. 1). Prior to this the commercial yields were usually low (1). The price paid to the grower has fluctuated between $3 to $6 per kg in recent years. Virtually all seed produced is used in Australia and indications are that the domestic market is unlikely to require more Haifa seed. There is great potential therefore for Australian (and especially Victorian) white clover seed producers to export Haifa and to grow overseas cultivars for re-export.

Figure 1. Certified seed production of Haifa white clover in Australia, 1977-1990.

The Neuarpurr district of western Victoria is well placed for white clover seed production. It has an excellent supply of good quality artesian water and has no white clover seed contamination - a major problem in many countries. The aim of this experiment was to determine whether successful seed crops of overseas cultivars of white clover could be produced at Neuarpurr. In addition the opportunity was taken to assess a wide range of material for seasonal herbage production and cyanogenic potential. The presence of cyanide may contribute to pest resistance but low cyanide types are favoured under certain climatic or edaphic conditions (2).

Methods

An experiment was established to determine the seed yield, seasonal growth and cyanogenic potential of a range of white clover cultivars, under spray irrigation at Neuarpurr in north-west Victoria. Forty-eight white clover cultivars from 16 countries were sown on 15 May 1988. The sowing rate was 4 kg/ha and the plots were 5x1 m. The design was a randomised block with four replicates.

The experiment was sown into a cultivated seedbed with 200 kg/ha of a 1:1 superphosphate-lime mixture containing molybdenum (0.05%). Tribunil was applied to control capeweed, Arctotheca calendula, in the establishment year. An additional 250 kg/ha of superphosphate was applied in spring 1989. Weeds (mainly Ox-tongue, Picris echioides) were controlled with Sprayseed in June 1989. Sufficient beehives were located near the trial during flowering to allow for a high rate of pollination.

Seed production was measured by direct heading in January 1989 and January 1990. On the first occasion, material collected with a lawn mower was thrashed. On the second, three 15x15 cm quadrats per plot were cut with hand shears and thrashed.

Clover yield was visually assessed in spring 1988 and in winter 1989. Plots were rated on a 1 to 9 scale where 1 = poor and 9 = excellent herbage production.

The cyanogenic potential of the herbage (dried at 65C) was measured using the modified picric acid procedure developed at CS IRO, Armidale (Pickering, unpublished data). All cultivars in replicate 1 were measured in September 1989 with selected cultivars (covering the range of cyanide levels found on the first sampling date) re-analysed in November 1989.

Results and discussion

All results are presented in Table 1.

Seed yield

First year seed yields were low due to adverse climatic conditions which also saw commercial yields fall. It is likely the yields were reduced by the choice of harvesting technique. Only five cultivars gave seed yields at least equal to Haifa. In the second year, seed yields were in the range 488-1,291 kg/ha with all but eight cultivars yielding as much seed as Haifa. These results suggest that successful seed crops of overseas white clover cultivars can be grown at Neuarpurr for re-export.

Clover yield

In 1988, 27 cultivars had spring growth scores equal to Haifa while in winter 1989 all but seven cultivars produced as much herbage as Haifa.

Cyanogenic potential

Cyanide levels in one replicate in September, 1989 ranged from 13-1398 g HCN/g DM while in November, 1989 the cyanide levels for each cultivar had fallen consistently by a factor of 5 to 6 reflecting the increased maturity of the foliage and the increasing temperatures. This agrees with the findings of Vickery et al. (3) who showed that leaf maturity and high temperatures were among the factors leading to a decrease in cyanide content of white clover. A wide range of cyanide production potential was to be expected amongst the cultivars as HCN levels have been shown to be related to geographic origin (2).

The authors believe that the results reported here support the development of a white clover seed re-export industry based at Neuarpurr. Most of the overseas cultivars were capable of producing high seed yields especially in the second year when the harvesting technique was successful. Seed producers need to be aware of the differences in maturity type between the overseas cultivars and the Australian cv. Haifa and manage the crops accordingly by delaying the closing and harvesting times for the later maturing cultivars.

Table 1. Seed production, rated clover production and cyanogenic potential of 48 white clover cultivars at Neuarpurr, western Victoria (N=not assessed).

Acknowledgments

The technical support of F. Snell, W. Feely and N. James is gratefully acknowledged, along with the financial support of the Wool Research and Development Corporation.

References

1. Simons, I. 1981. In: Growing Sub or White Clover for Seed. (Ed. R. Hill) (South Australian Department of Agriculture). Agricultural Note Series 105. pp. 626-5.

2. Williams, W.M. 1987. In: White Clover. (Eds M.J. Baker and W.M. Williams) (CAB: International). pp. 299-321.

3. Vickery, P.J., Wheeler, J.L. and Mulcahy, C. 1987. Aust. J. Agric. Res. 38, 1053-1059.

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