Many technologies are converging which allow growers to manage spatial variability. The question is largely one of economics. The techniques and technology required to identify field variation include soil surveys, yield monitors, positioning systems, soil sampling, sensors, computers and equipment with the capability of applying variable rates of agricultural inputs. Season variation is much more difficult to assess and manage because it involves predicting the weather and extrapolating these effects on crop production. Other interactions, such as diseases, insects, and other pests, can influence season variation.
Variability is measured by evaluating discrete sites in a field over time.
Yield monitors along with global positioning systems do a very good job of measuring field variability. Yield maps help assess the amount of variability and help to define a management area from which various input levels can be recommended. Field yield maps over many growing seasons will estimate season variability. Below is the data for four sites in a six-acre field over the last ten seasons. Each site measured 30 feet by 35 feet and had been cropped continuously to corn since 1983.