Soil profiles can change over time. Advisors are seeing some weak areas in northern California orchards and checking your soil profiles first.
Cooperative Extension Farm Advisor Emeritus Joseph Connell says they have seen tree yellowing in northern California, and looking at the soil composition is a must do if an area of production begins to look unhealthy. Connell says this cannot show you a soil change, but it can help you dial in your water use and limit unwanted leaching.