Kelp diredctly from a beach contains large amounts os salt, which is not good for the soil.
In Ireland we have used this product, not only as a fertilizer , but, also as a food called " dulsk", and it is becomming qiute a gourmet food now. Very tasty, great for stews etc,.
Best to wash the kelp in fresh water, dry, and shred to as small a size as possible. Them add to compost as part of a conditioner over the winter months, and it should be ready for your patch in the following season. Full of trace elements etc, but the easy way to get the value from this product is to buy liquid seaweed from your local store.