Spatio-temporal investigation of surface soil hardness on professional football field

The present study was conducted to identify the minimum number of sampling points to monitor surface hardness of the pitches through geostatistical methods and to determine spatial and temporal distribution of surface hardness in autumn, winter, spring, and summer periods. Initial samplings were performed from 126 points and with data reduction, the optimum number of sampling points was identified as 77. In upcoming sampling periods, surface hardness and soil temperature were directly measured in situ and disturbed soil samples taken from 77 points were subjected to moisture content, bulk density, and texture analyses (clay-C, silt-Si, and sand-S). In autumn period, surface hardness highly correlated with soil temperature and moisture content (r² = - 0.438 and - 0.344, p < 0.01). Surface hardness significantly correlated only with soil temperature in winter period and only with bulk density in summer period (respectively r² = - 0.366 and 0.234, p < 0.01). Average surface hardness values in autumn, winter, spring, and summer periods were respectively measured as 5.99, 6.55, 5.84, and 5.92%. Semivariograms generated for hardness were modeled with spherical model in all periods and a certain nugget effect was detected in all periods. Maximum likelihood distance for autumn, winter, spring, and summer periods was respectively measured as 65, 40, 45, and 46 m. It was concluded based on present findings that geostatistical methods could reliably be used to monitor surface hardness of football pitches and then proper and timely interventions could be made to sections not complying with FIFA standards.