Nutrient Management Research Database

This short newsletter covers the following topics:

• Diagnosing nutrient deficiencies
• Applying fertilizer
• Handling and application of olive mill waste products.

Nutrient Deficiencies

Of the 16 essential plant nutrients, only nitrogen (N), potassium (K), and boron (B) are the only likely to require supplemental applications. Further, K and B deficiencies are quite rare. 

Two methods for identifying nutrient deficiencies are commonly used in olives: 1) tissue analysis and 2) visual inspection. 

For tissue analysis, about 100 fully developed leaves should be gathered in July from the middle of non-fruit bearing current year shoots. You can find a list of local reputable labs by contacting your local cooperative extension agent.  

Visual inspection can be useful to identify deficiencies, though it requires training to become familiar with the symptoms of particular nutrient deficiencies. 

Check out the source to see the descriptions of N, K, and B deficiencies in full along with a key for interpreting tissue analysis results. 

Fertilizer Applications

Generally speaking, most olive growers will only need to apply N fertilizers. Mature olive trees require between 40-100 lbs N/ac yearly. 

Organic fertilizers are able to supply nutrients at a slow, continous pace. However, predicting he amount of nutrients present that will become plant available can be challenging. Legume cover crops are another potential organic fertilizer source, as they can supply about 25-30 lbs N/ac if properly managed.

Potassium can be found in composts and manures. Potassium sulfate applications at a rate of 500-1000 lbs/ac are generally applied in December or January. Efficient fertilizer rates can be achieved by applying K as a concentrated band just inside the drip line, as soil can tie up K and limit plant availability.

Boron deficiency can be corrected by applying 25-50 lbs of 14-20% B material per acre. A single broadcast application inside the drip line can be effective for several years. 

Olive Mill Waste

Since olive waste generally has a high C:N ratio (approximately 30:1), it requires supplemental N to compost properly. A ratio of 1 part chicken/dairy manure to 3 parts olive pomace will ensure slow composting. 

Applying moderate amounts of olive mill waste during the dry season helps limit environmental issues associated with soil run off containing high amounts of dissolved carbon.

Foliar Application

Foliar applications are unlikely to be successful unless nutrients are severely deficient are applied with other amendments already being applied.

The fertilizer rates noted here are for mature trees, to adjust the rates for younger trees use the canopy coverage. For example, a three year old tree with only 10% canopy coverage should receive 10% of the fertilizer.