Definition - What does Amendment mean?
In horticulture, an amendment is any organic or inorganic additive that improves soil conditions. There are many instances where a soil amendment may be required and it is a common practice in gardening.
MaximumYield explains Amendment
Plants require certain soil conditions in order to grow and thrive, but not all soils in the garden have these conditions. That’s why a gardener needs to add a soil amendment.
Compost and manure are commonly used soil amendments, as they are rich with organic matter and nutrients.
Soil amendments are also used to raise or lower the pH of soil. Lime is a commonly used amendment for acid soils and gypsum or pine straw will lower the pH for a more acidic soil.
There are also instances where the soil may be lacking in micronutrients, so amendments that contain those might be added.
Knowing the exact conditions the plant requires in order to grow well is essential in deciding just what type of soil amendment is needed.
There are also cases where the soil can actually be too rich or too high in organic matter for plants. For example, plants like butteryfly weed thrive in extremely poor soil conditions, so the soil amendment in this case would be sand or gravel.