What do we call man-made substances used in farming to enhance crop growth?

The term used to describe man-made substances that are specifically designed to enhance crop growth is "artificial chemicals." These substances are formulated to provide essential nutrients, support plant health, and optimize agricultural productivity. Artificial chemicals can include a variety of fertilizers and growth enhancers which are synthetically produced to improve soil quality or to directly supply plants with the nutrients they might be lacking.

Herbicides, on the other hand, are a specific type of pesticide used to kill unwanted plants or weeds, while pesticides generally refer to any chemicals used to control pests, including insects and diseases. Organic nutrients refer to natural substances derived from plant or animal matter that do not include synthetic components. Therefore, while all the other options are related to farming and may contribute indirectly to crop growth, "artificial chemicals" accurately describes the broad category of synthetic substances specifically used for enhancing plant growth.