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Seed yield of two white clover (Trifolium repens L.) cultivars grown in different row spacings : A thesis submitted in partial fulfilment of the requirements for the Degree of Master at Lincoln University

Ross, Jessica
Fields of Research
ANZSRC::300403 Agronomy , ANZSRC::300406 Crop and pasture improvement (incl. selection and breeding)
This investigation compared the seed yield of two cultivars (‘Legacy’, ‘Quartz’) of white clover and related these to morphological development and light interceptance in different row spacings (30, 45, 60 cm) and light regimes (north and south). This experiment at AgResearch, Lincoln in Canterbury, New Zealand ran from 17th March 2021 until a final (mechanical) harvest on the 25th February 2022. The development of tagged stolons was monitored weekly. Light interception and ground cover were recorded weekly until canopy closure. In addition, three destructive harvests were taken to capture key morphological characteristics of stolon length and seed yield from stolon, hand (quadrat) and mechanical harvests. Above average rainfall immediately prior to harvest resulted in low yields, which was consistent with regional commercial white clover seed yields. ‘Legacy’ produced more seed (792 kg/ha) than ‘Quartz’ (552 kg/ha) when harvested by hand. However, ‘Quartz’ may have had a higher seed potential because it had more juvenile buds and flowers present at desiccation compared with ‘Legacy’. Later desiccation of ‘Quartz’ would enable further flower ripeness and seed yield and it is hypothesised it may then have had seed yields comparable or higher than ‘Legacy’. The ‘Quartz’ phyllochron was 17.5°Cd less than ‘Legacy’ and it had a faster node appearance and stolon extension rate with more branches produced. This resulted in more leaves and total stolon length at stolon harvest compared with ‘Legacy’. An increase in row spacing or the sunny side of rows (north) may have resulted in microclimates, with increased soil surface temperature and light quality. Altered morphological traits due to agronomic decisions (row side or spacing) did not translate into higher seed yield, probably due to poor pollination and the wet conditions during harvest. Higher dry matter and leaf nitrogen was produced by ‘Legacy’ while ‘Quartz’ had more morphological structures (branches) to increase intercepted PAR. The environment of wider rows enabled the expression of these morphological characteristics for ‘Quartz’ and delayed critical leaf area which was favourable for flower development due to light quality. ‘Legacy’ had fewer branches and may produce higher yields when sown in narrower rows that achieve critical leaf area quickly to optimise PAR interception that can be converted to seed yield. Surprisingly leaf size did not differ between cultivars on the two dates it was sampled. However ‘Quartz’ exhibited many traits associated with smaller leaved cultivars while ‘Legacy’ responded as a larger leaved cultivar. ‘Legacy’ achieved critical leaf area quickly in narrower rows suggesting this cultivar is suitable for grazing systems however this poses challenges for seed production due to greater biomass production and subsequent shading from leaves.
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