Sometimes the PH of the urine produced is a big factor. If a urine is more alkaline is has a tendency to burn the grass. High meat diets create acidity that helps this problem. However female dogs and hormones do affect this to cause the grass to yellow.
There are some products out there to change acidity, one is called Grass SAver, and it uses Methionine, which is an amino acid. This Methionine is also what the vet uses to "overacidify" when treating Male cats for FLUTD. They would use high amounts to do this.
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