Why is yield not always a good indicator of soil fertility?

Yield is not always a reliable indicator of soil fertility because it can be influenced by a multitude of factors that are not directly related to the soil's nutrient capacity. For instance, weather conditions, pest infestations, disease outbreaks, planting techniques, and even market demand can drastically alter yield levels from year to year or from one field to another. Consequently, a high yield in a specific season does not necessarily mean that the soil is fertile; it may be a result of optimal growth conditions or effective pest management, while a lower yield could result from adverse weather despite having fertile soil. Therefore, assessing soil fertility effectively requires a comprehensive analysis that goes beyond just the yield figures, taking into account these various external influences.