In the Osage Hills of northern Oklahoma (south central USA) it is common practice to mow native grass meadows in autumn, but whether this is best management was unclear. This study, undertaken on the Adams Ranch (a 13,355 ha prairie range), compared two meadows mowed at different times of the year (summer or early autumn) to assess how composition, forage production and plant vigour are affected by mowing date.
Dominant grasses were big bluestem Andropogon gerardi, little bluestem A.scoparius, indiangrass Sorghastrum nutans and switchgrass Panicum virgatum. One meadow was traditionally mown annually around 1 July for hay. The other (6 ha) was mown annually in late August-early September.
In 1961 and 1962, the point intercept method was used to determine percent basal cover and species composition by area. Abundance was determined in 100 randomly located 30 x 30 cm quadrats per meadow.
Forage production was determined by clipping vegetation within 20 (29 x 61 cm) quadrats, drying and weighing. Vigour of important plant species was assessed by measurements of: maximum height, average height, leaf length, width and number.
In both years, the meadows were considered in excellent range condition, species composition was very similar and there was no correlation between mow date and basal density (both about 10 %).
Of 12 grasses recorded, little bluestem was most abundant (58.5-68.5 % composition). Big bluestem contributed higher percent composition in the July-mown meadow (average 43.5% over the study years) compared to the later mown meadow (10.9 %).Conversely indian grass was more common in the late-mown meadow (average 15.0 %) compared to the July mown meadow (5.5 %). Contributions of other grass species were similar between meadows.
In both years the July-mown meadow produced more forage (average 3,806 lb/acre dry weight) compared to the later mown meadow (2,141 lb/acre).
Mow date appeared to affect plant vigour in that grasses in the July-mown meadow had (statistically) significantly greater maximum height, average height and leaf length compared to the same species in other meadow.
Although the same forb species occurred in both meadows, their abundance was markedly different in each. The later mown meadow had a far greater number of forbs (240,887 vs. 89,522/acre), and its dominant species were uncommon in the July-mown meadow.