The persistence under grazing of 9 late maturing subterranean clover cultivars was monitored for 7 seasons at two long growing-season sites in south-west Western Australia. At both sites, plots of the new cultivars, Denmark Goulburn and Leura, maintained significantly higher varietal purity and both total clover and sown clover seedling densities than the older cultivars, Mt Barker, Karridale, Woogenellup, Junee, Larisa and Green Range. The higher seedling regeneration abilities of Denmark and Goulburn, in particular, provide a means of reducing the autumn-winter feed gap common in the long growing season areas of Western Australia.
In 1987 four trials were established in the long growing season zone of Western Australia as part of a national evaluation program of late maturing breeding lines of subterranean clover (Trifolium subterraneum L.). Initially 9 breeding lines, all introductions from Sardinia, were compared with 6 commercial cultivars. Data collected during the first 3 seasons from these trials was used to recommend the release of Denmark and Goulburn as new cultivars for the long growing season areas of Western Australia. Leura was also selected as a new cultivar for use in eastern Australia. Trial results from the first 3 seasons are presented in Nichols and Nicholas (1). These indicated that over a 3 year period, the new cultivars regenerated much more densely than the older cultivars. Plots of the 3 new and the 6 older cultivars were subsequently monitored at two of these sites for a further 4 seasons to measure longer term persistence. Regeneration results for year 7 from these trials are reported here.
Trials were sown in May, 1987, at Mt Barker Research Station and on a farm 5 km north of Manjimup. Plots measured 2 m x 5 m with 4 replicates of each variety. Other site details and measurements taken for the first 3 years can be found in Nichols and Nicholas (1). From December, 1989 onwards, trials were grazed by sheep in common with surrounding paddocks. In January, 1993, seed bank reserves were sampled. From this seed 100 seedlings derived from each plot were germinated in the glasshouse and their identities compared with control cultivar seedlings. No attempt was made to identify subterranean clover types not originally sown in each plot. In early May, 1993, subterranean clover seedling regeneration counts were taken at both sites, using five 25 dm2 quadrats per plot.
Mean total subterranean clover regeneration density was significantly higher at Manjimup than Mt Barker (Table 1). Over both sites plots of Denmark and Goulburn were significantly denser than all other cultivars, apart from Leura. Mean purity was similar at both sites, although a highly significant site x cultivar interaction was found (Table 1). Denmark plots maintained the highest purity, with more than 97% of Denmark seedlings at each site, but did not differ from Goulburn and Leura plots. Karridale was the only other cultivar not significantly different from Leura and Goulburn. Denmark and Goulburn also had significantly greater seedling densities of the sown subterranean clover type (Table 1) than all other cultivars apart from Leura.
These results indicate that the greater persistence of the new cultivars of Sardinian origin, Denmark, Goulburn and to a lesser extent, Leura, found over the first 3 years of these trials (1), continued for at least 7 seasons. The higher maintenance of plot purity of the new cultivars also indicates greater competitiveness than the older ones against background or invading types. This has particular implication for farmers sowing into paddocks with resident oestrogenic subterranean clover. Nichols and Francis (2) suggest several reasons why subterranean clovers of Sardinian origin are well adapted to southern Australian farming conditions. These include a dense, leafy, relatively prostrate growth habit, enabling them to withstand heavy grazing, and a high seed setting capacity.
a * = significant at 0.05%, ** = significant at 0.01%, *** = significant at 0.001%, n.s. = not significant
Use of Denmark and Goulburn subterranean clovers in the long growing season regions of Western Australia is particularly benefiting farmers by producing higher seedling densities, translating into higher autumn clover herbage production and reducing the autumn-winter feed gap. Further work is ongoing to combine the persistence of Sardinian germplasm with improved resistance to diseases and red legged earthmite.
Both the International Wool Secretariat and the Grains Research and Development Corporation provided funds towards this work.
The effect of hybrids, soil types and applied phosphorus on the growth and tissue composition of pyrethrum (Tanacetum cinerariifolium L)
A glasshouse experiment compared the shoot mineral composition and shoot, root and flower growth response to applied phosphorus (P) fertiliser (0, 50 and 100 mg P/kg soil) of three new pyrethrum hybrids (Cross-5, Cross-10 and Cross-3×11) with a standard hybrid (Cross-3) when grown on four soils (low and high-P ferrosols and vertosols). The yield of Cross-3×11 and Cross-10 on low-P ferrosol was 2.5 fold and that of Cross-5 1.3 fold greater than Cross-3. On the high-P ferrosol Cross-3×11 and Cross-10 gave 25% and Cross-5 19% higher dry matter yields than Cross-3. On the vertosols all hybrids gave similar yields. Application of P increased the yield by 10-200%. The P and potassium (K) concentrations in the shoot were correlated with the concentrations of these nutrients in the soil and were not affected by hybrids. Application of P increased soil Colwell P and P in shoot, root and flower. The study concluded that the new hybrids were superior in P utilisation on low-P ferrosols to the previous standard Cross-3 hybrid.
Pyrethrum (Tanacetum cinerariifolium L.) is a small perennial plant of the Asteraceae family cultivated for the extraction of a mixture of insecticides (Pyrethrins) from its dried achenes and has been commercially grown in Tasmania since 1981. Pyrethrins have low mammalian and fish toxicity and rapid break down rate, and to date no insects are known to have immunity to them (1). Pyrethrins are mainly used for the control of household, food storage and medical and veterinary important pests.
Previous field studies in Tasmania investigated the effects of fertiliser P on hybrid Cross-3 (CIG-3), grown on a vertosol and a ferrosol (3). This hybrid Cross-3 is currently used as one of the parents in production of new hybrids. The two major soil types commonly employed in Tasmania for pyrethrum production are high P-fixing ferrosols and non P-fixing vertosols. Field observations indicate that some hybrids grown on ferrosols may perform well under low nutrient status, while others may thrive when an abundance of nutrients was available.
The objective of this experiment was to compare the yield response and changes in the mineral composition of three new pyrethrum hybrids with the standard hybrid (Cross-3) grown on two different soil types, each at low and high P level and different levels of applied P.
A glasshouse pot experiment was conducted as a completely randomised block with 3 replicates during September 1993 to November 1994. Three kg soil (oven dry basis) was weighed, mixed with P fertiliser and placed into 4-L pots. The soils used were from top 150 mm of two ferrosols and two vertosols from north western and southern Tasmania respectively. One of each soil types was low and the other was high in the available P as measured by Colwell and Donnelly (2) (Table 1). One pyrethrum seedling at 6-leaf stage was transplanted into each pot. The new hybrids (Cross-3×11, Cross-5, and Cross-10) were compared with the standard hybrid Cross-3. The pots were watered to 80% of field capacity routinely throughout the experiment when moisture levels had fallen to 50% of field capacity. Phosphorus was applied as diammonium phosphate (DAP, 20% N, 18% P) at 0, 50 and 100 mg P/kg soil. All pots were adjusted for the applied N immediately after planting and supplied with 100 mg K/pot and 150 mg N/pot monthly through irrigation water.
At harvest, flowers, shoots and root material were separated, dried at 60°C and weighed. Sub-samples of plant dry components were ground and analysed for P, K, calcium (Ca), magnesium (Mg), sodium (Na), sulfur (S), zinc (Zn), boron (B), iron (Fe), and manganese (Mn). Soil samples were taken before the start and at the conclusion of experiment (bulked for the hybrids) for Colwell extractable P and K.
Table 1. Soil Colwell P and K concentration before the start and after harvest of the pyrethrum that had received different levels of P (mg /kg).
The dry matter yield of flowers, shoots and roots were significantly (P 0.02) influenced by hybrid, soil type and applied P. There were strong correlation between the DM yield of flowers and shoots (R2=0.72), roots (R2=0.63) and whole plants (R2=0.81). Similarly, in a field study on a ferrosol in northwestern Tasmania (5) a strong relationship (R2=0.7) was observed between yield of flower and the yield of whole plant. The dry matter yield of whole plant (yield) is discussed here.
On low-P ferrosol, all three new hybrids out-yielded the standard hybrid (P<0.01). The yield of Cross-3×11 and Cross-10 on low-P ferrosol was 2.5 fold and that of Cross-5 1.3 fold greater (P<0.01) than Cross-3. On high-P ferrosol, the yields of Cross-3×11 and Cross-10 were 25% and Cross-5 19% higher (P<0.01) than that of Cross-3 (Figure 1). On vertosols all hybrids gave similar yield with both low and high-P soils, except for the yield of Cross-3×11 on high-P vertosol that was 12% higher than Cross-3 (Figure 1).
Ozanne et al. (3) reviewed plant factors affecting P utilisation by plants. The difference in the efficiency of species in uptake of P was attributed to the morphology of root and root hair, weight, length and distribution of roots in the soil and the ability of plant to establish symbiotic associations with mycorrhizae. The reason for the low efficiency of Cross-3 hybrid in utilisation of P from low-P ferrosol could not be determined in this study. Further work is necessary to explain the differences. As Cross-3 is one of the parents of the new hybrids, it seems that its low P utilisation characteristic has not been fully transferred to the new hybrids.
Phosphorus application significantly (P<0.001) increased the yield regardless of hybrid, soil type and soil P level. On low-P ferrosol, without applied P, the yields of new hybrids were similar and were 67% higher than Cross-3. With application of 50 mg P/kg the yields of Cross-3×11, Cross-10 and Cross-5 were 2.9, 2.1 and 1.1 fold that of Cross-3. With 100 mg P/kg, the trend was similar for the hybrids, but yield increases were only slightly larger than that with 50 mg P/kg rate. On high-P ferrosol application of P increased the yield by less than 10% and there was little or no difference between the 50 and 100 mg/kg rates.
On either low- or high-P vertosols, there was little or no difference in yield response to P between hybrids. Yield responses to 50 mg P/kg ranged between 10 and 30% and little or no yield increases were observed when applied P was increased to 100 mg/kg.
Plant species or hybrids vary in their ability to use soil or applied P to produce their maximum yield. Ozanne et al. 1980 in a field experiment, comparing two crop and two annual pasture species, found a range of nearly fourfold in the level of applied P required for the maximum yield. In the current study the differences in response to applied P between hybrids was only observed on the ferrosols. This may indicate that soil P fixation had influenced the uptake rather than the hybrid differences.
Figure 1. Effect of soil type on dry matter yield of root (black segment), shoot (grey segment) and flower (white segment) of pyrethrum hybrids. Bars on the columns represent the LSD.0.05 for the effect of hybrid on whole plan dry matter.
Figure 2. Effect of application of phosphorus at 0 (grey), 50 (white) and 100 (black column) on dry matter yield of pyrethrum hybrids grown on four different soils. Bars on the columns represent the LSD.0.05 for the effect of phosphorus and that above the columns represents the LSD.0.05 for the interaction of phosphorus and soil type.
Colwell P after the experiment was similar or slightly lower than at the start, but application of P increased (P=0.02) Colwell P) above that without applied P (Table 1). The Colwell K was reduced by up to 65% (Table 1) in the treatments with high DM yield, including those with applied P, showing that applied K have not been sufficient and the soil K reserves have been accessed by plants.
Mineral composition of plant tissues was influenced by soil type (P 0.02) and in most cases and especially for the shoot (Table 2) it reflected the soil available nutrients. There was little or no difference between the composition of hybrids. The mean mineral composition of tissues (Table 2) indicated a significant (P 0.05) difference in concentration of most elements in shoots, roots and flowers.
Application of P increased P concentration in shoots, roots and flowers, but had no effect on other elements in the root and flower. With application of P, the shoot concentration of Ca and Mg increased and that of K decreased and the concentration of other nutrients was not affected. Shoot P and K were moderately correlated with soil P (R2=0.5) and soil K (R2=0.6).
The low K concentration in the shoots could have been due to an insufficient supply of K to satisfy the high K demands resulted by higher dry matter production in response to the application of P. The increase in Ca and Mg concentration may have been the result of K deficiency.
Table 2. Effect of soil type on mineral composition of pyrethrum shoot and the average composition of shoot, root and flower.
The new pyrethrum hybrids that are currently commercially grown in Tasmania were clearly superior in the yield production to standard hybrid Cross-3 when grown on ferrosols, the major soil type used for pyrethrum cultivation in Tasmania. However, on the vertosol the yields of all hybrids were similar. The hybrids in order of efficiency of utilising P from ferrosols were Cross-3×11> Cross-10 >Cross-5>Cross-3. These findings suggest that the forms of P in the soil and the ability of hybrids to utilise those forms of P governed the hybrids differential soil P utilisation.
I would like to thank the Botanical Resources Australia and the Horticultural Research and Development Corporation for their funding of the work. I would like also thank Barry Rowe and Peter Gillard for their comments.