Seed production and seedling establishment in rhizomatous clovers

Abstract

Seed production was measured from four seed lines of rhizomatous clovers, Caucasian clover (T. ambiguum) cultivars Alpine (diploid) and Monaro (hexaploid), and zigzag clover (T. medium) seed lines Porters Pass and Kentucky in 1987/88 (first year), 1988/89 (second year) and 1989/90 (third year). Flowering patterns and seed yields were studied in all three seasons. Seed yield components were studied in the second year. In the three year old plants the effect of six closing times on seed yields, seed yield components and dry matter yields were investigated in the third year.

The experimental design in 1987/88 and 1988/89 was a randomised block design with two replicates, and a split-plot design was used in 1989/90. The eight plots, each measuring 3.75 X 10m, had five rows of plants at 1m and 0.5m inter- and intra row spacing respectively. In 1989/90, each plot was divided into six sub-plots to accommodate six closing treatments. The soil in the trial area was Templeton Silt Loam with 31% (w/w) field capacity. In 1988/89 and 1989/90, 20mm and 40mm of water was applied through irrigation on 20 December and 15-16 December respectively. No irrigation was applied after post-harvest. In 1989/90, superphosphate was applied on 3 October 1989 at the rate of 200 kg/ha. Crops were sprayed with herbicides on 14 February 1989 and 26 June 1989. During the 1989/90 flowering period plants were sprayed twice with the insecticide 'Marvarik' on 21 December and 19 January.

Climatic conditions over the 1987/88, 1988/89 and 1989/90 experimental periods (Sept-Feb) fluctuated considerably. The 1988/89 period was much warmer and drier than the other two periods.

On average Alpine Caucasian clover flowered six days earlier than Monaro. This could be due to difference in their ploidy levels. In zigzag clover, there was little variation in flowering pattern between Porters Pass and Kentucky over the three seasons. Alpine Caucasian clover was about two weeks and three weeks earlier in flowering than zigzag clovers in the second and third year respectively. Timing of flowering and its duration varied from one season to another. In the second year, all seed lines flowered earlier than the other two seasons. This was probably due to the high temperatures and dry conditions that prevailed during flowering period; flowering rate was also enhanced and flowering periods were shorter compared with the other two seasons. In the first two years, zigzag clovers had a low seed yield. The study of seed yield components in the second year showed that this was caused by fewer seeds produced per head. About 57% of seed-pods were without seeds. In addition about 42% of total seeds present were destroyed by chalcids in the second year. The average seed yield in zigzag clovers increased threefold, from 80kg in the second year to 250kg/ha in the third year. This was attributed mainly to chalcid control (reduced to 33%) and better management practices such as fertilisation, irrigation and weed control. More favourable climatic conditions may have also helped.

Except in the first year when plants were small, Caucasian clovers produced good seed yields. Monaro produced the highest seed yield of 398 kg/ha in the second year of production.

In the third year, seed yield in Caucasian clovers was significantly increased by vegetative closing. In Alpine and Monaro, seed yield increased from 160 to 228 kg/ha and 398 to 560 kg/ha respectively compared to uncut plants. In zigzag clover, however, seed yields were similar in uncut and vegetative cut plants. Porters Pass and Kentucky had the highest seed yields of 210 kg and 304 kg/ha respectively from vegetative cut. Closings at flowering stages greatly reduced all seed yield components, causing a large reduction in seed yield of all seed lines.

Dry matter yields were measured in the third year at the time of closings, seed-harvest and four months after harvest. Most of the dry matter yield was produced in spring/early-summer. Zigzag clovers produced more dry matter than Caucasian clovers. All seedlines produced more dry matter with later closing treatments than the vegetative cut closing time.

The highest total dry matter yield of 8.9t/ha was produced by Porters Pass from uncut plants. Post-harvest yield was very low, which was mainly due to slow regrowth after harvest and lack of rain in summer and autumn.

A laboratory germination test of scarified and non-scarified seeds of rhizomatous clovers was carried out to determine the advantage of mechanical seed scarification. The average germination percentage was increased from about 8% to 70% by seed scarification.

In autumn 1989 (22 March), seed was sown into Templeton silt loam and seedling growth was studied. The highest seedling emergence was only 52% in Monaro. About half of the emerged seedlings were killed by frost lift during winter. Seedling growth measured over autumn, winter and early spring was very slow and all four seedlines had a similar pattern of growth. Early seedling root growth was more rapid than top growth. Two months after sowing, the mean root to leaf petiole length ratio of four seedlines was 2.4:1, but five months later it declined to 1.4:1. This indicates that the slow top growth in rhizomatous clovers at the initial establishment stage was probably due to higher under-ground activity which was more apparent in Alpine Caucasian clover.