A variety of factors can cause brown patches on lawn. Although one of the most common is dog urine, don’t go blaming Fido just yet. Firstly, make sure that your lawn is properly irrigated. That means that it should be getting enough water. Remember that enough means not too much but not too little either. This is very important. Too little water and the grass can dry up. Too much of it, and you can effectively drown your grass. Either way, you can end up with brown patches on the lawn. To test the water level, you can simply stick your finger in the ground and see how much moisture is there. If your first finger is damp when you pull it out, the water is just right. Any more or any less than damp means that you have a problem.
Also, brown patches on the lawn can be the work of fertilizers not being absorbed the way they should be. That means that fertilizer, especially synthetic one, is dissolving much slower and gathering at the roots of the lawn. This prevents grass from properly reaching the soil and getting the other nutrients it needs, causing it to wither and turn brown. You can check for this too by doing a test on a small patch of lawn and seeing how your regular fertilizing and watering routine affects it.