In Germany, athletic fields need a high water infiltration rate since soccer is played during the winter when the soil is saturated. In the summer, moisture is deficient so a high water-holding capacity is needed. The various layers used to construct the field should accommodate these two extremes.
Fertilization of a compact, stony, subsoil underlying a drainage layer and a surface rooting layer with calcium cyanamide increased turfgrass growth, improved appearance, and increased drought resistance with the effects continuing into the third year. A layer of peat, perlite, and vermiculite on the subsoil also improved turfgrass appearance and increased drought resistance.
Drainage layers constructed of lava or pumice had a higher water-holding capacity than gravel and therefore delayed the onset of wilt. Turfgrasses wilted 3 days later on lava and 8 days later on pumice as compared to gravel.
The composition of the surface rooting layer, based on the new German Norm DIN 18 035-4, should be as follows. Not more than 8% fine soil (0.02 mm), less than 4% organic matter (weight percentages), a water-holding capacity between 35 and 40% by volume, and an infiltration rate of more than 0.0015 cm/second.
If Hygromull (BASF, West Germany) is used in place of one-third of the peat in a high peat mix (40% by volume), the surface layer will be firmer and the Hygromull will supply additional nitrogen. An increase of the water-holding capacity of a surface layer without an effect on the infiltration rate is possible by substituting lava sand, pumice sand, or perlite for quartz sand.
The infiltration rate of a mixture containing well-decomposed peat was much lower than for a mixture using undecomposed fibrous peat. A high infiltration rate resulted in the improved quality of the turf, especially when inferior varieties of Poa pratensis were used. Additional index words: Calcium cyanamide, Fertilization, Hygromull, Peat, Perlite, Pumice, Sand, Water infiltration rate, Water-holding capacity.