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.