If your lawn looks like it has a brownish dead like appearance after cutting it with your Husqvarna/AYP riding tractor it is most likely due to dull blades. When the blades get worn out or dull they shred the ends of the grass instead of cutting it cleanly. The shredded tip can turn brown making it look like your grass is dying for several days. The green color will gradually come back to entire lawn as the grass grows.
To keep this from happening, sharpen or replace dull blades at least once a season, depending on how often the riding tractor is used.
The tag that has the model and serial number of your Husqvarna/AYP riding tractor can be found under the seat.
NOTE: if you need a part for the small engine in your Husqvarna/AYP lawn tractor, there will be a separate model/serial number for the engine. Here are the small engines that are available in your Husqvarna/AYP tractor. Visit the page of the engine you have to find out where the model/serial number is located for your small engine model: