Olive Tree Nutrition

Olive Tree Nutrition

A comprehensive description of olive grove nutrient needs and testing can be found in Chapter 9 (Fertilisation), pp267-297, of the Olive Growing Manual (El Cultivo Del Olivo): https://australianolives.com.au/olive-growing-manual/

More specifically, sampling is addressed in 9.3 (soil in 9.3.1, leaf in 9.3.2) and fertiliser application in 9.6 (soil in 9.6.1, foliar in 9.6.2). Additionally, 9.4 is a useful guide in terms of putting a fertilisation plan together.

According to the UC Davis Olive Centre:

Olive trees need 16 essential elements to fulfil a cycle of growth. An olive orchard’s supplemental nutritional needs vary depending on soil fertility, orchard age, soil composition, nutrients in irrigation water, and cultivation practices.

Leaf nutrient levels vary normally throughout the growing season – some accumulate, some are relatively static, and some diminish. In addition, annual variations in nutrient levels can occur for other reasons, such as the crop load, water availability in the soil, crop management techniques, and interactions between nutrients.

Nutrient deficiencies observed in California olive orchards have been limited to nitrogen, and, rarely, potassium and boron. Nitrogen is the only nutrient supplement that might be needed on an annual basis. Investigate the cause of a mineral deficiency, because the solution is not always to simply provide fertilizer.

Determine orchard fertilization needs through annual leaf tissue analyses and visual deficiency symptoms. For annual leaf tissue analyses, collect at least 100 leaves from several trees in each homogenous area of an orchard from the middle of non-bearing, current-season shoots. Low nitrogen levels are visually indicated by poor shoot growth (less than 20 cm) and leaves with a light green-yellow shade, but must be verified by an objective, quantitative leaf tissue analysis.

Seek to achieve nutrient levels consistent with the following table:

Table. Critical nutrient levels from July (November in Australia) olive leaf tissue analysis from sub terminal leaflets of current year’s non-fruit bearing growth.

Element Deficient Sufficient Toxic
Nitrogen (%) 1.40 1.50 – 2.00
Phosphorus (%) 0.10 – 0.30
Potassium (%) 0.40 > 0.80
Calcium (%) > 1.0
Magnesium (%) > 0.10
Manganese (ppm) > 20
Zinc (ppm) unknown
Copper (ppm) > 4
Boron (ppm) 14 19 – 150 > 185
Sodium (%) > 0.20
Chlorine (%) > 0.50

Avoid applying fertilizers if leaf tissue nutrient levels are adequate. Excessive fertilization increases production costs, nutritional imbalances and environmental pollution.

Fertigation, the application of fertilizers dissolved in irrigation water, is the most efficient fertilizing method. Fertigation delivers nutrients to areas of greatest root activity and density, maximizing a tree’s nutrient absorption. Fertigation requires cleanliness and irrigation system maintenance, because some fertilizers can clog the system. Fertigation with some fertilizers can also increase soil salinity.

Organic fertilizers such as compost or cover crops have advantages in releasing nutrients slowly year-round, developing soil structure and aiding water infiltration, but also may require additional water (e.g. for a cover crop). Any fertilizer can leach nutrients during cold and rainy periods (when trees are not taking up nutrients) and allow nitrogen runoff into water resources.

Ed: Before embarking on a tree nutrition program OliveCare® suggests olive growers test soil pH (which impacts on nutrient availability) and also undertake a leaf analysis to identify critical deficiencies – leaf analysis is best taken in the summer months when the tree is actively growing. Also read Paul Vossen’s comments below on the impact of soil moisture and weed competition.

What is important is to take the leaf analysis at the same time each year so that the test results can be compared and trends identified.

Soil pH test kits can be ordered from Bunnings have a similar kit available Australia-wide at half the price and no postage – https://www.bunnings.com.au/manutec-garden-care-products-soil-ph-test-kit_p3016727 – right click to open hyperlink

Notes: low pH (acidic) soils can be treated with applications of lime.

High pH (alkaline) and sodic (high sodium) soils can be treated with gypsum followed by irrigation to leach the displaced sodium.

Leaf analysis tests are used to monitor the nutritional status of the trees, evaluate the effectiveness of fertiliser applications and to identify potential nutritional problems before they occur.

Soil and leaf nutrient analysis services are available from a number of laboratories including:

Interpreting test reports:

NSW DPI: How to interpret your soil test – right click to open hyperlink

APAL: Soil test interpretation guideright click to open hyperlink

SESL: Interpreting a plant analysisright click to open hyperlink

Haifa website:  There’s lots of useful information available on olive growing with a focus on tree nutrition: Crop Guide – Olives: https://www.haifa-group.com/olives-fertilizer

Ed: There are also lots of useful snippets of information around leaf testing and nutrition in an article on the continuing Olives NZ Focus Grove Project in the coming June edition of Olivegrower & Processor.

Paul Vossen on olive tree nutrition:

There is an interesting article on olive tree nutrition by Californian olive specialist Paul Vossen at: https://ucanr.edu/sites/SoCo/files/27175.pdf

In summary, Paul states that nutrition is less important than water for olive trees.  He says that olive trees are NOT big feeders, they are hardy and well adapted to poor and shallow soils, and tolerant to a wide range of soil pH conditions:

 “Deep fertile soils that would be important for above-standard growth and production for other orchard crops are actually a negative for olives. In these soils, olives tend to be excessively vigorous vegetatively, grow too tall, and produce little fruit. When excess shoot growth is pruned to keep olive trees smaller, they respond by sending out long, vigorous, non-fruitful shoots, in most cases. Olive trees trend to fruit better under conditions of low vigour including minimal nutrition without being deficient. They respond quite amazingly to adequate irrigation water with good growth, large fruit size, and much better yields without making any changes to their nutritional status. They also do much better with no weed competition.

Paul recommends leaf analysis to determine if there are any nutrient deficiencies – the most likely is Nitrogen (N).

“The important thing about nitrogen is to make periodic applications in accordance with leaf analysis and to achieve adequate shoot growth of between 20-50 cm. Nitrogen may not need to

be applied every year. It can carry-over in the soil for several years, especially in heavy clay. In sandy soils it tends to leach and can cause ground water and run-off pollution, so make sure not to apply too much at once – lighter frequent applications are better. Conventional nitrogen fertilizers such as urea, ammonium nitrate, ammonium phosphate, ammonium sulfate, potassium nitrate, or calcium nitrate also work. As a starting point, nitrogen is normally applied, at the following approximate rates (per tree or per ha based on large wide-spaced mature trees of 375 trees/ha).

For other tree spacing use the per ha rate.

  • 3 to 0.7 kg. of urea (46%) per tree – 100 to 250 kg. per ha
  • 4 to 0.9 kg. of ammonium nitrate (33%) per tree – 136 to 340 kg. per ha
  • 6 to 1.5 kg. of ammonium sulfate (21%) per tree – 216 to 540 kg. per ha
  • 7 to 1.8 kg. of CAN-17 (17%) per tree – 267 to 668 kg. per ha
  • 8 to 1.9 kg. of sodium nitrate (16%) per tree – 284 to 710 kg. per ha
  • 8 to 2.0 kg. of calcium nitrate per tree (15.5%) – 293 to 733 kg. per ha
  • 9 to 2.3 kg. of potassium nitrate per tree (13%) – 349 to 875 kg. per ha
  • 1 to 2.7 kg. of ammonium phosphate per tree (11%) – 412 to 1,033 kg. per ha

“For dry-farmed trees, nitrogen fertilizers should be put on just before a rain in mid to late winter. Under irrigated conditions, it can be applied periodically throughout the growing season and watered in. For drip irrigation it can be placed right under or through emitters.

Foliar Snake Oil: Paul has some critical words on the use of foliar fertilizers:

“Most of the time, what happens from most foliar sprays is that higher levels of nutrients occur in the leaf for a short time, usually just a few weeks. There is usually, however, no measurable effect on shot berries, fruit set, shoot growth, number of flowers, number of perfect flowers, fruit yield, or fruit size. Many comparison trials all over the world have looked at foliar nutrition in olives for many years. In most cases, foliar sprays also have no effect on alternate bearing. Foliar applied compost tea will not control or prevent peacock spot on olives nor has it been shown to have any other positive effect. This whole lack of effect is predicated on having adequate nutrition from the beginning, which again, is very easily and inexpensively achieved by ground application. So, unless there is a demonstrable benefit, foliar feeding is a useless expense of tractor, spray equipment, and labour.”