Published online by Cambridge University Press: 12 June 2017
Red clover (Trifolium pratense L.) was direct seeded into a grass sod after spraying with dalapon (2,2-dichloropropanoic acid), glyphosate [N-(phosphonomethyl) glycine], or paraquat (1,1′-dimethyl-4,4′-bipyridinium ion) at rates of 5.6, 2.2, and 0.6 kg ai/ha respectively. Dalapon applied a few days prior to planting did not improve red clover stands in comparison to seeding in unsprayed sod. Applying glyphosate a few days prior to seeding in spring and summer invariably increased red clover stands, but paraquat was effective in only one of four spring or summer applications. Glyphosate applied the fall preceding a spring or summer seeding produced red clover stands superior to those after all spring treatments. Where glyphosate or paraquat was applied, water content of the upper 20 cm of the soil profile was greater during the first 10 days after treatment, relative to unsprayed plots or those treated with dalapon. By 30 days after application, the glyphosate-treated sods used less soil water than those treated with paraquat. Applications of glyphosate and paraquat greatly suppressed water utilization by oats (Avena sativa L.) in the greenhouse, based on water potential of the potting soil. Dalapon had little effect on water use by oat seedlings in the greenhouse.