Influence of Tripping, Soil Moisture, Plant Spacing, and Lodging on Alfalfa Seed Production¹

Pollinating Bees (Hymenoptera: Apiformes) of U.S. Alfalfa Compared for Rates of Pod and Seed Set

“…Female M. rotundata tripped 83% of visited alfalfa ßowers in an extensive Þeld study of commercial seed alfalfa near Nyssa, OR (Kemp and Bosch, unpublished data), a value in close agreement with the present greenhouse study (78%). These differences could be the result of environmental conditions imposed by the greenhouse, particularly the warmer, moister air, which inßuences the tripping mechanism, as does soil moisture in which the alfalfa is grown (Tysdal 1946, Lesins 1950, Loper 1972. Bees ßying in the conÞnes of the greenhouse probably had curtailed foraging ßights as well, which could have altered their accumulation and transfer of pollen.…”

Recurrent Selection for High Self‐Fertility in Vernal Alfalfa (Medicago Sativa L.)

“…Gray (I925) found that wind tripped alfalfa blossoms, but Knowles (19^3) found no correlation between tripping and wind velocities. Tysdal (1946) found 7 percent of the flowers were tripped by rain.…”

“…However, both Tysdal (1946) and Knowles (19^3) considered rain unimportant as a practical tripping mechanism since crossing did not occur during rain. Stewart (1934) believed that alternating spells of cloudy and brircht weather with moderate wind and occasional showers were favorable for tripping, and Piper et al (1914) found bright sunshine induced tripping.…”

“…Certain field husbandry practices have been shown by Tysdal (1946) to affect seed production in alfalfa. Lowest seed production resulted when plants were thick and irrigated frequently.…”

Photosynthate Allocation to Floral Nectar: A Neglected Energy Investment

“…McGregor and Todd (1952, as cited in Shuell975) estimated a peak daily nectar production of 54-238 kg/ha for alfalfa. If this nectar averaged 40% sugar (Vansell 1942), 22-95 kg sugar (3.6-15.7 x 10 8 J) would be contained in the nearly 5 x 10 9 florets of a hectare (Tysdal 1946). However, peak nectar production in alfalfa would occur only over 1-2 d, and reduced rates of production would ensue during the rest of the days of blossoming (Shuel 1975, Southwick andSouthwick 1983).…”