Submitted to: Crop Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 9/30/1999
Publication Date: N/A
Interpretive Summary: Significant amounts of a birdsfoot trefoil seed crop can be lost at harvest time if the pods shatter before harvest. This research determined how seed shattering is related to irrigation practices and climatic conditions at the time of seed harvest. Increasing amounts of applied irrigation water increased the percentage of the potential seed yield that would shatter by harvest time. This finding strengthens the argument that birdsfoot trefoil grown for seed in western Oregon should not be irrigated.
Technical Abstract: Seed shattering is a major problem in birdsfoot trefoil (Lotus corniculatus L.) seed production. The objectives of this research were to (i) quantify the effects of soil-water availability on seed shatter and (ii) determine optimal harvest time based on a heat unit method to minimize seed shatter losses under western Oregon climatic conditions. Irrigation treatments varying in water depletion percentage and replenishment amount were applied in 1994, 1995, and 1996 on a Woodburn silt loam soil (fine-silty, mixed, mesic Aquultic Argixeroll) near Corvallis, Oregon. The total amount of shattered seeds was correlated with total harvested seed yield. Manipulation of the reproductive development pattern by different irrigation treatments did not affect the times of peak seed shattering events. The crop water stress index (CWSI) was inversely related to the percentage of total seeds shattered at harvest time. Increasing amounts of applied water increased the percentage of the potential seed yield that would shatter by harvest time. Seed shatter losses fluctuated during the late reproductive development period but were not influenced by the irrigation treatments. Fluctuations were also observed for average temperature, relative humidity, and vapor pressure deficit, but did not predict the times of multiple peak seed shatter events. A total of 109 HU using a 10 deg C base temperature (approximately 11 d) accumulated from the time of initial pod dehiscence until rapid seed shattering initially occurred. The average seed yield losses due to shattering from pod dehiscence was 3 to 5.3 kh/ha/day.