Minecraft wiki entry for Dried_Kelp_Block, associated text: Dried kelp blocks have a 50% chance of increasing the compost level in a composter by 1. Composting a dried kelp block instead of 9 dried kelps is less efficient. For example, 100 dried kelp blocks would yield 7 1⁄7 bone meal on average. Crafting them into 900 dried kelp before composting would instead yield 384⁄7 bone meals on average.