A dog's nose is usually moist and cold. There are a number of reasons why a dog's nose may be dry or cracked, and not all of them are serious.
A dog's nose can become dry and cracked if he is dehydrated. Make sure the dog has easy access to a regular water source, especially if he spends time outside during hot months.
Your climate can lead to your dog having a dry, cracked nose. Very cold winters are especially damaging to sensitive tissues. Hot, dry summers can dry out the tissues or even cause sunburn on the nose, which can lead to cracking.
Some dogs are allergic to certain plastics used in their food dishes. One symptom of the allergy is a dry and cracked nose. You can remedy this by switching to a metal dog dish.
Dogs can get infections in their noses that lead to flakiness or crusty patches. Infections can both cause dry noses or running sores. Loss of pigmentation is another sign of an infection.
You can apply unscented lotion to a dog's dry or cracked nose. Put sunscreen on the nose of a dog that will be out in the sun for long periods of time. Consult your veterinarian if the dog's nose is dry or cracked continuously.