Answer to Question 1
The number one problem with root zones for highly trafficked turfs is compaction. The primary design criterion is material that resists compaction. Sand is the material of choice. Fine sands make excellent root zone materials and should be selected for their uniformity of particle size. Sand by itself is not the only material used in root zones. Soil and/or organic matter, such as peat, is also added in small quantities to add water and nutrient-holding capacity to the final mix.
Answer to Question 2
The economic threshold level is the point at which the pest infestation requires immediate, intensive control to prevent unacceptable aesthetic changes. The key to the answer is that threshold is a measure of pest population or density. The damage threshold level is also a measure of pest population or density that initiates some change in aesthetic quality. This includes any change not just an unacceptable level. In practical terms, the damage threshold level is always reached before the economic threshold level. The turf manager should monitor a turf for changes above the damage threshold level. This gives he/she an early warning system for the economic threshold level.
A hypothetical hybrid zone.
During confrontations with others, the mane makes the lion look larger.
Tissues and Regions of the Root Tip
What makes tea so good
The San Andreas Fault Zone
"Practice makes perfect"