When you apply organic fertilizers, there's no need to dig them deep into the soil. Plants's feeder roots are mostly near the soil surface, and low oxygen levels deep in the soil would retard microbial growth, slowing nutrient release from organic fertilizers. Make an exception to that no-dig rule if a soil test shows that phosphorus levels are low. This nutrient moves very slowly, so the only way to spread it quickly through the root zone is to mix it into the top 6 to 12 inches of soil. Always wear a dust mask when you apply bonemeal, guano, or any other type of fertilizer that's dusty.
All dusts are potential lung irritants.
How Much to Apply The actual amount to apply will vary, depending on the results of a soil test and the rate of nutrient release from a particular fertilizer. Kinds of Organic Fertilizers In catalogs and garden centers, you can find many different kinds of organic fertilizers. Other kinds are either custom blends, or materials that are available in limited quantities or only regionally. These fertilizers can be considered renewable resources, but you should take into account the resources that may have been needed to grow as well as process or transport them. Some, such as beet pulp and cottonseed meal, are by-products of other industries.