Seed production of Lotus tenuis (Fabaceae), a forage legume: effects of row spacing, seeding date, and plant defoliation

Abstract

Indeterminate flowering, pod dehiscence, and seed shattering are some the most important factors that limit seed yield in some Lotus species. The objective of this study was to determine strategies to maximise Lotus tenuis seed yield by evaluating: (i) the effects of row spacing (17.5 and 35.0 cm) and seeding date (autumn 2007, autumn 2008, and spring 2008) on vegetative biomass and reproductive components, and (ii) plant defoliation at the beginning of flowering to make the time of seed ripening more uniform. Plant density was held constant at 20 plants/m2. The beginning of flowering was later in plants seeded in spring than in those seeded in autumn. Defoliation retarded peak flowering through destruction of reproductive organs. Vegetative and reproductive biomasses were not significantly different between row spacings or defoliation conditions. Vegetative biomass, seed yield, pod dehiscence, and shattered seed varied between seeding dates in different years, and within the same year between seeding seasons. Harvest seed yield was greater for autumn 2007 than for spring 2008 and autumn 2008 seeding (181.67 ± 9.76, 71.41 ± 4.16, and 41.73 ± 3.39 g/m2, respectively). Lost seed (shattered seed) was greater for spring 2008 than for autumn 2008 and autumn 2007 (76.04 ± 5.29, 71.43 ± 3.31, and 16.11 ± 2.61 g/m2, respectively). Under defoliation conditions, harvest seed yield and lost seed were 92.59 ± 3.07 and 2.07 ± 0.63 g/m2, respectively. Potential seed yield was highly correlated with avoveground vegetative biomass (R2 = 0.758; P < 0.0001), no. of umbels with pods/m2 (R2 = 0.859; P < 0.0001), and pod biomass/m2 (R2 = 0.949; P < 0.0001). Thousand-seed weight was not significantly different between row spacings, but was greater with spring seeding and lower if the crop was defoliated. Air temperature and relative humidity during reproduction affected seed shattering and, consequently, seed yield. The results are discussed in relation to the management of L. tenuis seed crops and the importance of row spacing, seeding date, and plant defoliation for seed production.