Pistachio Potassium deficiency
Estimating soil nutrient content
The major challenge with all soil analyzes is calibration of the soil test with crop performance.
Field kits: See the NRCS soil field guide Link There are a number of field kits for estimating soil nutrient content ranging from the very cheap to the expensive. See example kits Link
Laboratory methods. : The American Society of Agronomy have a series of excellent publications outlining laboratory methods for soil analysis Link
There are six macro-nutrients essential for plant growth
Nitrogen and Phosphorus are the most commonly deficient macro-nutrients. Potassium is also increasingly deficient - especially in heavily cropped areas.
Plant deficiency symptoms: Plant visual symptoms often are one of the best indicators of possible deficiency or excess (Link).
Soil pH: Soil pH can be a good indicator of the probability of a nutrient deficiency Link (requires flash)
Simple tests for identifying deficiencies: There are a number of simple tests for identifying possible plant nutrient deficiencies (Link)
Video Nutrient deficiencies in plants (from Univ Manitoba)