Most often fertility will not be a cause of yield variability, but it is information we need to know. Data on pH, organic matter, CEC, phosphorus, and potassium can be very helpful. Look for areas where lower yields may be from areas that have high fertility. Compaction Operating equipment on a wet soil can compact the soil, destroy its structure, and reduce crop yield. A compacted soil layer will generally have poor structure, and most of the voids in this layer will have been eliminated.
Voids are open spaces between soil particles filled with air, water, or a combination of both.
Soil water will tend to accumulate above the compacted layer because movement of water through the compacted area is severely restricted. Root growth is also restricted, which reduces tolerance to dry weather. Compacted areas may be hard to define on a yield map, but keep in mind areas of heavy traffic and equipment operation in wet conditions. Naturally Occurring Variables 1. Weather Weather is the largest factor affecting crop yield.