Perennial crops especially benefit from leaf analysis because trees and vines store nutrients in roots, trunks, branches, and leaves, therefore, not receiving all of its immediate nutrients from the soil. A clear picture of what the crop is experiencing – from weather and disease to soil and water – can be seen from a leaf analysis. In combination with soil and water analysis, leaf analysis is a powerful tool to managing your crop effectively and efficiently.
Generally, leaf analysis is done annually. For analysis of plants in southern California, leaves should be collected between August 15th and October 15th, or when a fully expanded leaf is present, which is when the leaf is approximately four months old. Leaves of this age have been found to most accurately reflect how the crop is assimilating nutrients. Young leaves can be high in potassium and nitrogen, but low in zinc and iron. On the other hand, more mature leaves can show high levels of zinc and iron but be low in potassium and nitrogen.
Leaf analysis is useful with helping growers manage nutrient input. It can aid in determining, if necessary, required fertilizer application types and rates and help diagnose problems that may result in poor crop yields. Results from leaf analysis can be compared with known standards to determine whether the tissues contain excessively high or low concentrations of critical macro and micro nutrient elements. The nutrient supply can then be adjusted to bring the levels of the mineral nutrients in the tissues back to within acceptable limits.
Healthy crops typically have high stem density and bright green leaves. Crops with leaves showing discoloration may be the sign of a nutrient deficiency. The appearance of apparent mineral deficiency symptoms may be the result of an actual deficiency or could be caused by several other conditions or combinations of conditions including:
- Insufficient or poor soil moisture distribution and/or topsoil erosion.
- Poor drainage and subsequent restriction of the root system.
- Insects, disease, fertilizer burn, weeds or compaction of the soil - all of which weaken the root system.
- Periods of cool weather during the growing season.
Injury from herbicides.
None of the above conditions should exist before making additional fertilizer applications.