Boron Application in Olive Trees.
AT FLOWERING
At this time of year it is imperative to apply foliar applications of Boron and Calcium. A lack of Boron and Calcium may lead to decreased fruit set, & fruit quality.
The application of Boron and Calcium can never be overstressed. It is a requirement for your trees. Soil & Leaf Analysis will determine your soil and trees avaliable boron levels. Low Boron levels identified would then need to be addressed to maximise yeild and quality.
BORON IN SOILS
Soil organic matter is the major reserve of boron (B) in most soils. It is released as the soils organic matter decomposes, its availability fluctuating according to soil microbial activity.
In the soil solution, boron is present in a non-ionic form [B(OH)3], and is not attracted to soil colloids. It is one of the most mobile nutrients in the soil, and can be rapidly leached once released from soil minerals and organic matter. Soils in high rainfall areas are often low in boron.
BORON IN PLANTS
Boron is taken up by plants as undissociated boric acid [H3BO3 or B(OH)3]. It plays a role in cell wall development, and is important in pollination, fruit development and the translocation of sugars. An adequate supply of boron is important at flowering. Fruit quality is affected in olives if boron is deficient.
Within plants, boron is relatively immobile. It is not readily relocated from old to young plant tissue. Plants are therefore dependent on continuous uptake of boron during the growing season. In this respect, its behaviour in plants is very similar to calcium (both are immobile) and deficiency symptoms can be confused.
DEFICIENCY SYMPTOMS
Boron deficiency occurs more commonly in dry weather. Microbial activity in the soil is reduced, and the movement of boron in the soil solution to plant roots is restricted.
Olive trees are susceptible to boron deficiency. Consequently, boron is commonly recommended in routine fertilizer applications for high return croping.
Because boron is relatively immobile in plants, deficiency begins at the growing points.
Symptoms include :-
Chlorosis (yellowing) and death of the growing points.
Distortion, thickening and cracking of stems. The stems may be hollow or brittle.
The formation of rosettes, growth of auxiliary buds (side shooting), bushy growth and multiple branching.
The thickening, twisting and failure of roots to spread out or develop properly. In some cases the roots may show excessive branching.
The dropping of buds or blossom. Fruits and seed may also be affected. Brown sunken areas may develop in fruit.
The range between deficient and toxic levels of boron is very narrow.
TOXICITY SYMPTOMS
In the early stages, the symptoms of boron toxicity are normally expressed as marginal and tip chlorosis of the older leaves. Moderate to severe toxicity produces progressive leaf necrosis beginning at the tip or margins and gradually covering the whole leaf, resulting in premature leaf drop. One of the most common causes is over-fertilization with or poor placement of boron fertilizer.
BORON FERILIZERS
Borax, (11% B)
Is a fine crystalline product for dry application by hand to the soil, or application in solution to the soil or foliage. Borax is not as common as it was in the past.
Granubor, (15 % B) and
Borate Granular, (14.3 % B)
These are granulated fertilizers which makes them more suitable for dry application by machine to the soil. They can be used on their own or in blends with other fertilizers. Granubor and Borate Granular no not dissolve are unsuitable for foliar application.
Solubor, (20.5 % B) - A fine soluble powder for application in solution through a boom-spray to the soil or
foliage. Application rate 1 to 1.5 grams per litre, apply spray till runoff is achieved. Solubor is more soluble than Borax, especially in cold water, and is the recommended choice for foliar applications or ground applications in solution.
AgroDex Boron, (10%) Is a high analysis Boron solution, designed to rapidly correct boron deficiencies in both soil and foliar applications in all crops. AgroDex Minerals are derived from the most potent materials available and undergo a complex process allowing enhanced foliar and root zone uptake. AgroDex Boron is formulated with a blend of growth factors and organic acids, which assists with assimilating Boron in the plant.
Application rate: 1 to 2L/Ha. Can be applied as a Foliarspray, Fertigated or Irrigated.
APPLICATION
Because of its mobility in the soil and susceptibility to leaching, annual, or more frequent applications of boron
are recommended in most situations. Frequent applications at low rates also minimise the risk of toxicity.
In tree crops, the boron should be spread or sprayed over the root zone, i.e. under the whole canopy and
just beyond the area of the tree canopy, but no closer than 30 cm to the trunk. Toxicity may occur if it is
applied unevenly, i.e. it is concentrated in small areas.
In horticulture, e.g. tree and vegetable crops, foliar sprays, e.g. of Solubor, are often used to supply boron
instead of applying boron fertilizers to the soil.
A study on olive trees has looked at different application rates of Boron and Calcium and the effects on fruit set.
The rate of 100ppm of Boron and 2% Calcium was applied at full bloom and the 2nd application at 15 days later. Trees were sprayed with nutrient solution till run off.
EFFECTS ON FRUIT SET
Trees in this study showed a higher fruit set. Results also confirm the role of boron and calcium nutrients in improving fruit set of olive flowers.
From the overall data, the two studied nutrients effectively increased fertilization either through controlling pollen germination on the stigma or growth of pollen tube through the style. Therefore, subsequent increase in fruit set percentage was observed.