Seed development and the influence of severity and date of defoliation and plant population upon seed yields in 'Grasslands Maku' lotus (Lotus pedunculatus Cav.)

Abstract

Studies of Maku lotus seed production were investigated over two seasons on a fertile silt loam to sandy loam soil complex (pH 6.1, Olsen P 24) at Lincoln College, Canterbury, New Zealand (43º 38'S).

Seed development investigations showed that the optimum time to commence harvesting was two to four days after seed maturity, when the seeds had 35% moisture content, the pods were light brown in colour and three to four per cent pod shatter had occurred. Pollination to seed maturity (maximum 1,000 seed dry weight; 0.70 g 1982, 0.71 g 1983) took 27 days in 1982 and 35 days in 1983. High daily temperatures and vapour pressure deficits caused rapid seed ripening in 1982 and increased pod shatter from 4%, 31 days after pollination, to 82%, 43 days after pollination. Cooler weather in 1983 resulted in slower seed ripening and reduced pod shatter to only 13%, 47 days after pollination.

Cutting to ground level after spring growth commenced significantly reduced Maku lotus seed yields. Maximum seed yields were from uncut treatments, 47 g m⁻² (1982) and 49 g m⁻² (1983). Cutting to ground level (a) before bud appearance (September 29th, 1982 and October 20th, 1982) reduced seed yields (28 g m⁻² and 14 g m⁻²), and (b) after bud appearance (from mid-November to mid-December 1981 and on November 11th 1982) produced negligible yields. In 1982/83 topping before bud appearance produced seed yields (40 and 41 g m⁻²) which were not significantly different from uncut treatments (49 g m⁻²). Topping after bud appearance significantly reduced seed yields (26 g m⁻²) compared with the uncut treatment. The results indicate that Maku lotus should not be cut after spring growth commences, if maximum seed yields are to be achieved.

In the first year of establishment, plant populations of 22 and 33 plants metre⁻² in 0.45 m and 0.30 m inter-rows, produced significantly higher seed yields (86 and 88 g m⁻²) than populations of 66 and 133 plants metre⁻² in 0.15 m inter-rows (61 and 63 g m⁻² ). The evidence suggests that in second and subsequent years, Maku lotus plant populations of 22 plants metre⁻² or less in 0.45 m inter-rows will produce maximum seed yields.