Fig. 4. Probability of frost-seeding success (P), as measured by the frequency of sites for which the value of increased May forage yields exceeded the cost of seed, as a function of seeding rate (SR). Regressions were: Perennial ryegrass, P = 0.951 - 0.144ln(SR), R² = 0.72, P = 0.07; Orchardgrass, P = 0.722 + 3.4 x 10^-5SR - 7.9 x 10^-7SR², R² = 0.99, P < 0.01; Reed canarygrass, P = 0.391 - 0.062ln(SR), R² = 0.75, P = 0.06; and Smooth bromegrass, P = 1.787 - 0.268ln(SR), R² = 0.98, P < 0.01