A study of the effects of plant spacing and irrigation on seed production and seed development in Siratro (Macroptilium atropurpureum) : a thesis presented in partial fulfilment of the requirements for the degree of Doctor of Philosophy in Seed Technology at Massey University, Palmerston North, New Zealand

Thumbnail Image
Open Access Location
Journal Title
Journal ISSN
Volume Title
Massey University
The Author
Since 1980 the Thai government has been interested and active in increasing livestock production by improving the productivity and quality of natural and sown grassland. The introduction of forage legumes, particularly Siratro (Macroptilium atropurpureum), is one of the ways in which this can and is being achieved. The present study was carried out in two parts - the first involving two field trials conducted in Thailand during the wet and the dry season, and the second involving a controlled climate study at Palmerston North (N.Z.). The aim of the field trials was to investigate the effects of plant spacing, and during the dry season the effect of irrigation on Siratro seed production. In the controlled climate study a more detailed investigation was undertaken of the effects of water stress on plant growth and development and subsequent effects on seed yield. Particular attention was also given to relevant aspects of seed development in the latter study. Irrigation during the dry season produced relatively small but significant increases in plant dry weight and LAI and led to a sig­nificant increase in seed yield by the final harvest 40 days after peak flowering. By comparison, plant spacing had a marked effect on plant components and seed yield showing a negative response on a per plant basis but a positive response on a per unit area basis with increasing plant density. During the longer growing period of the wet season experiment, plant growth was substantial and again showed the same significant responses to increasing plant density stated above. Maximum seed yield per hectare was achieved at very high plant population densities approxi­mately 15 x 15 cm spacings. The major contributions to seed yield in both trials were inflores­cence numbers and especially pod numbers, reflecting their sensitivity to water stress and plant competition. Numbers of seeds per pod and individual seed weight were relatively insensitive to those environ­ mental factors. The growth room study clearly showed that early and extended soil moisture stress can cause a severe reduction in plant weight, branch development, leaf number and LAI, leading to a significant reduction in seed yield. However, soil moisture stress imposed at peak flower­ing resulted in a significant increase in seed yield compared with adequate moisture to final harvest. This beneficial effect was again due mainly to the increase in the number of inflorescences and pods formed on the primary and particularly the secondary branches. Numbers of seeds per pod and individual seed weight were again un­affected by water stress. The development of Siratro seed followed two obvious phases viz the growth and food reserve.accumulation phase and the ripening phase. Water stress reduced the time from anthesis to seed maturity and increased the percentage of hard seed at harvest when imposed early at the mid- vegetative stage. Plant spacing and irrigation had little or no effect on seed quality characteristics of Siratro, as quality appeared to be more dependent on stage of maturity. High seed quality can be achieved by harvesting Siratro 20 - 30 days after peak flowering. The possibility of growing Siratro for seed production in Thailand is also discussed.
Forage plants, Legumes, Legumes as food