Are compost and fertilizer the same?

Compost and fertilizer are not the same. But compost does have fertilizer value.

Wikipedia describes fertilizer as any material of natural or synthetic origin that is applied to soil or to plant tissues to supply one or more plant nutrients essential to the growth of plants.”

Compost’s nitrogen, phosphorus, and/or potassium (a.k.a. NPK) values are low compared to a synthetic fertilizer.  Some may add ingredients like urea to hike these macronutrient numbers.

That said, compost’s NPK value does have dollar value. The nutrients delivered by a compost product should be a factor in any input decisions involving synthetic fertilizer purchases.  Compost also adds a slew of micronutrients not typically found in common synthetics and improves nutrient uptake.

Compost feeds the soil. In turn, the soil takes care of the plants, offering a smorgasbord of nutrients, pest and disease resistance, and more.   But those nutrients are slow-release, feeding plants over time.  The benefits of a single compost application can stretch over multiple seasons.

Fertilizer’s sole purpose is feeding plants.  The primary function of most synthetic fertilizers is adding N, P, and/or K.  Application gives an immediate burst of nutrition.

Do you need fertilizer if you use compost?

For the home gardener, probably not, especially if that gardener is a long time compost user.

But for a commercial grower?  Maybe.  If the crop likes a punch of nitrogen (for example) at a certain point in the growth cycle, the addition of a synthetic fertilizer may be warranted.

However, the smart grower will carefully weigh the cost of any input against the expected return on investment. Sometimes, a lower yield will still net higher profits if input costs for synthetic fertilizers and pest control products are reduced or eliminated as a crop management expense.

Also, keep in mind that compost-amended soil reduces rainwater and irrigation runoff, which means more nutrients are retained in the soil.   This will impact synthetic fertilizer input requirement, as well.

Read it.  Amended attitude: a new commitment to soil health using compost, written by Gary Gittere and recently published by SportsTurf Magazine.


Human activity and development destroy topsoil.  When topsoil goes, so does the soil’s natural ability to withstand the ravages of wind and water.  The result is erosion, and the by-product is sedimentation.
The wash and settling of soil particles reduces storage capacity of reservoirs.  Sediment clogs drainage ditches and navigation channels.  It buries fertile bottomland in sand.
This damage can make flooding worse. The cost of supplying drinking water and using water for generating electricity rises.
The USDA says sediment is “the greatest pollutant of waters in the U.S. by volume.”  Sedimentation is a costly thing to fix.  Mitigating the impact of sedimentation in the U.S. alone is in the billions of dollars.
Of course, humans aren’t responsible for all sediment loss.  Natural forces also erode stream banks and change shorelines.  But people do more than their share.
By one estimate, as much as two-thirds of sediment loss may result from the activities of people.
Compost use cuts sedimentation
Compost use reduces the impacts of farming, logging, development and other land disturbance.  It can also temper nature’s contribution to the problem.
Compost formulated for erosion control absorbs both rain energy and water.  When compost blankets are used, the amount of soil retained approaches 100 percent.  Water runoff is reduced by as much as 50 percent.
The place to focus sediment control is not on a river bed or estuary floor after the damage has already been done.  The best strategy is to manage sediment at the source — land disturbance activities.
Let compost play a central role in sediment prevention or soil restoration strategies.