Typewritten copy Includes bibliographical references

Excessive growth by red clover, Trifolium pratense L., grown for seed interferes with maximum seed production and harvest in Oregon's Willamette Valley. This study was conducted during 1986 and 1987 on red clover cv. Kenland to determine if plant height and dry matter production could be inhibited and seed yields improved with the plant growth regulators (PGRs) uniconazol (XE-1019) and paclobutrazol (Parlay). The effects of different soil-applied and foliar-applied PGRs and application rates on plant height, crop biomass, and yield components of red clover were measured at Corvallis, OR on Woodburn silt-loam (fine-silty mixed mesic Aquultic Argixerolls) soil. Soil-applied PGRs were also managed under single and multiple irrigation regimes in 1986. Under a single irrigation regime in 1986, canopy height was reduced by 32% when XE-1019 was applied at 1.12 kg ai/ha and was reduced by 13% when Parlay was applied at 1.68 kg ai/ha. Averaged over the two-year period, straw yield was reduced 40% with XE-1019 (1.12 kg ai/ha) and by 12% with Parlay (1.68 kg ai/ha). Seed yield was increased by 11% with the lower XE-1019 rate (0.14 kg ai/ha) and was increased by 14% with the higher Parlay rate (1.68 kg ai/ha). Soil-applied PGR treatments reduced canopy height by 25% with XE-1019 (1.12 kg ai/ha) and was reduced by 11% with Parlay (1.68 kg ai/ha) under multiple irrigation in 1986. Straw yield was reduced by 30% with XE-1019 (0.84 kg ai/ha), but Parlay had no effect on straw yield. In addition, seed yield was increased by 8% with XE-1019 (0.56 kg ai/ha) and by 18% with Parlay (1.68 kg ai/ha). Foliar-applied XE-1019 (1.12 kg ai/ha) reduced canopy height by 13% in 1986 and by 25% in 1987, whereas foliar-applied Parlay (1.12 kg ai/ha) reduced canopy height by 9% in 1986 and by 19% in 1987. In 1986, seed yield increases averaged 16% across all 3CE-1019 treatments (0.07 to 1.12 kg ai/ha) and was increased an average of 21% across all Parlay treatments (0.28 to 1.68 kg ai/ha). However, 1987 was drier and warmer than 1986, consequently, foliar-applied XE-1019 reduced seed yields by an average of 23% and Parlay reduced seed yields by an average of 21%. Total dry weight and straw weight were unaffected by foliar-applied PGR treatment in both years. Use of XE-1019 and Parlay in field crop production has the potential to reduce dry matter production and improve seed recovery, but results vary from year to year. These PGRs have the potential to improve seed yields and may be effective in improving harvest conditions by reducing vegetative biomass. / Graduation date: 1995

Sweet clover plants become more susceptible to low temperatures as they advance in age. They are most resistant when in the crook stage. Plants resulting from unhulled seed are more vigorous and resistant to low temperatures than are plants resulting from scarified seed. Plants from unhulled seed produce larger bay yields and more profits than do similar plants resulting from scarified seed. Soils containing a medium percentage of moisture afford more optimum conditions for plant growth than do soils of extremely low or high moisture content. There is an indication, but not conclusive, that the physiological activity of seedlings from scarified seed is slightly more rapid than is the ease of imhulled seedlings. Alternate freezing and thawing of impermeable sweet clover seed, or treating with concentrated sulphuric acid, does not increase, to any significant degree, the percentage of germination. It seems that the subjection of seed to a moist condition is just as effective as any attempt to increase germination by artificial means. / M.S.

Unhulled white sweet clover seeds return larger yields of bay and greater profits than do similar scarified seeds. Seedlings resulting from unhulled seeds are more resistant to low temperatures than seedlings coming from scarified seeds. Sweet clover seedlings are most resistant to cold when in very early stages of development. They become more susceptible with advance in age. High soil moisture exerts a protective influence on seedlings which are in a susceptible stage of growth at the time of exposure to low temperatures. There is some evidence, although not conclusive, that seedlings coming from scarified seeds are more active physiologically than those coming from unhulled seeds. / M.S.