The effect of altitude on grass growth in east Scotland.
S23 perennial ryegrass was grown for 4 years in boxes on levelled sites at 250-ft altitudinal intervals from 500 to 2250 ft alt. Floral development was delayed by 1.3 days and annual yield by about 2% for each 100 ft increase in altitude. The yield decrease per 100 ft altitude was 5% in spring, 1.8% in autumn, and was absent in summer when highest yields sometimes occurred at higher altitudes as moisture stresses developed at lower altitudes. The extent of the altitude response differed for the 2 soils used. The effect of altitude on growth in spring and early summer appeared to be quadratic and related to temperature, effects being most pronounced near 42°F and decreasing as temperatures approached optimum values. Where unduly exposed sites occurred at low elevations, growth was always reduced. [See also abs. 2815]-R.B.