Analysis of temporal changes in cultivars of Poa pratensis subjected to football-type wear

Thirty cultivars of Poa pratensis were assessed for shoot density before wear, ground cover at the end of wear and reflectance ratio on 16 dates during wear. Analysis of the reflectance ratio × time interaction by split-plot analysis was shown to be invalid, but an analysis of polynomial orthogonal contrasts over time revealed significant interactions amongst cultivars. A trapezoidal method was used to calculate the area under the reflectance ratio against time graph to generate a single value of reflectance ratio during wear for each cultivar. Following the correction of this value for the influence of P. annua contamination, the trapezoidal area from the reflectance ratio measurements was significantly correlated with ground cover of P. pratensis (r = 0.73) at the end of wear, but not with shoot density before wear (r = 0.06).