Boron Deficiency in Oil Crops

Boron deficiency in canola

Canola (rape seed oil), like all its relatives in the Brassica family, has a very high boron requirement and is severely affected by boron deficiency. Canola seed production is critically dependent on boron—so much so that grain yields have been doubled when 2 lbs of boron per acre were applied to canola fields that showed no visual abnormalities.

Canola needs more boron through all growth stages—vegetative and flowering—than most other crops. Ensuring that canola has adequate boron will:

• Stimulate root growth and early establishment
• Enhance vegetative growth and speed maturity
• Increase branching and flowering
• Increase flower retention and pollen germination
• Enhance nitrogen utilization to increase oil percentage
• Increase the number of pods that set and fill

Although boron deficiency can markedly affect vegetative growth, it is more usual to find that yields are reduced by the deficiency even when the plants show no obvious symptoms. This is probably due to the fact that boron is required for pollination and because a slight deficiency can result in poor seed set, even though pods may be formed. Brown necrotic areas which form in the pith of the stem may be one of the earliest signs of boron deficiency.

When the deficiency is severe the new leaves will be very deformed; they may have cracked petioles and be bent back. Stem elongation will be restricted, the plants will be stunted, and ultimately the growing point may die. Branching may be excessive.

Boron deficiency in coconut

Leaf malformations caused by boron deficiency were first seen in the 1960s. They are shown by the youngest leaves and are more or less identical with the ones found in oil palms.

The symptoms, in increasing order of severity, are:

1. Fusion of terminal pinnae on the frond
2. “Hook” or “bayonet leaf,” in which the pinnae are bent into a double or single hook near the tip
3. Development of the fronds with very short pinnae either on one or both sides of the rachis
4. In the most severe cases, frond development without any pinnae

The first two symptoms are the most common. Occasionally, the apical growing point dies.

The first sign of boron deficiency on 1-year-old coconuts is the development of small chlorotic spots on the young leaves. These spots are symmetrically orientated in relation to the main veins on the leaf. These boron-deficiency symptoms on very young palms bear a striking resemblance to those on young oil palms.

Boron deficiency in Indian mustard

Boron deficiency causes young Indian mustard leaves to become deformed and curled. They are usually rough, thick, and leathery. The growing points die and axillary shoots develop, which themselves become moribund and die. In severe cases, flower buds shed prematurely and the flowers that form are likely malformed. In less severe cases, seed set is restricted.

Boron deficiency in flax linseed

The young leaves are chlorotic and, in cases of severe boron deficiency, the growing points ultimately die. Shoots will develop from many nodes. Growth is generally reduced and the stems may be:

• Thick
• Twisted
• Possibly fasciated

The tips of the shoots turn yellow, wilt, and die.

In old plants, the top part may be affected while the lower part remains healthy. Seed and straw yield is reduced and the fiber may be poor quality. Boron deficient flax appears more susceptible to Fusarium than healthy flax.

Roots are dark and short when boron deficiency is severe.

Boron deficiency in oil palm

Boron is the most common nutrient deficiency in oil palms. Boron’s primary role in oil palm is to act as a key component in several vital processes such as cell division, root development, cell wall formation, sugar transport, and calcium uptake.

Adequate boron is necessary for:

• Preventing “fishbone leaf” or “hooked leaf tip”
• Elimination of white stripe occurrence in leaves
• Preventing seedless fruitlet
• Adequate fresh fruit bunch formation
• Enhanced root growth

Boron deficiency symptoms for oil palm

Several symptoms of various leaf malformations are associated with boron deficiency. “Hook leaf” or "hooked leaf tip," which consists of a single or double hook on the pinnae, and transverse corrugations on the pinnae are usually the first symptoms to appear.

Fasciation, a flattened fan-like growth pattern, and the inability of pinnae to expand are associated with more severe boron deficiency in oil palms. The leaf tissue is fragile and the leaflets break easily, resulting in the condition known as leaflet shatter. With “blind leaf,” another symptom of boron deficiency, the pinnae develop incompletely as a tuft of bristles at the terminal end of the frond. A very severe boron deficiency results in “fishbone leaf,” identified by extremely small, thin pinnae. The breakdown of the growing point results in a dry heart rot as a final characteristic symptom.

On young seedlings, there are a few signs of boron deficiency. The dark green lamina is sprinkled with white dots and streaks, which become more pronounced on older leaves. There is a tendency for seedlings to show juvenile tendencies with the entire bifurcate leaf remaining undeveloped.

Boron deficiency in olives

Native to the Mediterranean region, tropical and central Asia, and various parts of Africa, olives require a long, hot growing season to properly ripen the fruit, no late spring frosts to kill the blossoms, and sufficient winter chill to insure fruit set. Olives are also grown commercially in California, Australia, and South Africa.

Olives will grow and produce fruit even on extraordinarily poor, stony soils, yet they respond to fertilizers.

Boron is a crucial trace element for olive trees. Fertilizing olive trees with adequate boron is necessary for:

• Flower formation
• Fruit set
• Quality olive oil
• Stable olive oil

Boron deficiency makes leaves fall and branches die in the upper parts of the tree. Secondary shoots develop at the base of the dieback, and the number of suckers in the lower part of the trunk increases.

The leaves show a distinct apical browning which can extend up to two-thirds of the leaf while the rest of the leaf remains a normal green color. Subsequently, the leaves may become completely yellow and later turn a leathery brown from the apex. In cases of mild boron deficiency, some fruit may ripen normally but most will drop prematurely or become deformed and corky. As the boron deficiency becomes more severe, the olive tree will become increasingly less productive and may ultimately die.

Boron deficiency in peanuts

Boron is critical to peanut quality. While boron fertilization may only occasionally improve peanut yields, it almost always is necessary for the prevention of “hollow heart” and other concealed disorders that severely reduce crop value.

Peanuts need a constant supply of boron during all stages of growth, but especially from flowering to harvest. Fertilizing with boron will help peanuts:

• Improve root nodule development for more nitrogen fixation and protein production
• Produce and retain more flowers and pegs
• Enhance calcium utilization
• Move sugars and protein from leaves to nuts
• Prevent “hollow heart”

Symptoms of boron deficiency are particularly evident in the nuts and are not frequently found on the foliage. While the effects on yield may be slight, a boron deficiency can markedly reduce the quality of the crop and the yield of marketable peanuts. The main symptom is a hollow darkening of an off-color area in the center of the cotyledon. Depending on the severity of boron deficiency, the depression may vary from being shallow and slightly colored to being deep and dark brown. Cracks may also develop on the pods.

The first sign of boron deficiency on the typically dark green leaves is the development of water-soaked areas, which give the leaves a mottled appearance. Prolific secondary branching occurs on short woody stems after dieback of terminal growing points.

When boron deficiency is less severe, flowers aren't followed by any fruit development, possibly as a result of pollen tubes failing to grow properly. When boron deficiency is extremely severe, flowers don't develop.

How much boron is enough?

• Peanuts are typically grown in light, sandy, well-drained soils, which are inherently low in organic matter, including boron
• Since boron is also readily leached from these soils, small annual boron applications are recommended to ensure an adequate crop supply during each growing season

Your boron fertilizer options

• Granubor^® is an ideal material for dry-blend fertilizers applied broadcast preplant or surface banded.
• Fertibor^® works best in fertilizer suspensions for preplant broadcast or band sprayed over the row.
• Solubor^® allows you the most flexibility for applying boron; it can be dissolved alone in water or in liquid fertilizers and/or pesticides, then applied to the soil or directly onto the foliage.*

Peanut fertilization

University research and field experience has led to the general peanut recommendation of 0.5 lb of actual boron per acre per year. Currently, the preferred practice is to split the fertilizer application by applying 0.25 lb of boron before the early bloom stage (tank mixed with leafspot fungicide or in the irrigation water) followed in two to four weeks at early bloom with another 0.25 lb. This ensures that boron is available to the peanut during flowering and fruiting, its time of maximum need.

As an alternative, 0.5 lb of actual boron per acre can be incorporated with other pre-plant, broadcast fertilizers or herbicides. Rates of boron fertilization should be based on soil tests and/or plant analyses, along with field histories, yield goals, varieties, and application methods.

Irrigated fields, or fields that have a history of serious "hollow heart," and/or fields planted to a high-yielding, large nut variety may benefit from split soil and foliar applications totaling up to 1.0 lb of actual boron per acre per year.

* Foliar sprays should not exceed 0.5 lb/acre boron per application.

Boron deficiency in soybeans

Boron is essential for all plant growth. Soybeans, like all legumes, have a high boron requirement. Boron is necessary for:

• Stimulation of root growth
• Increased soybean root nodulation development for nitrogen fixation
• Increased branching and flowering
• Increased bloom retention
• Increased number of pods
• Better seed development and grain yield

Soybeans are considered non-responsive to boron. And, soybeans appear to be sensitive to boron toxicity, especially when the boron is applied to the leaves. However, yield reductions do not necessarily accompany leaf spotting and marginal necrosis caused by excessive boron accumulation.

What does boron deficiency in soybeans look like?

As with many plants, the earliest sign of boron deficiency in soybeans occurs in the roots. The root tips die and new roots are initiated giving a rosette appearance.

Likewise, the death of the shoot growing point is followed by prolific development of lateral shoots with brittle petioles.

Boron deficiency in sunflower

Boron deficiency symptoms first appear on the youngest leaves which become progressively smaller and malformed. The stem is short due to lack of extension of the cells in the internode.

Distortion of flower heads is commonly seen and seed set on the head is very uneven—sections of the head may show no seed set at all. This symptom is associated with the boron requirement of the pollen tube.

When the deficiency is very severe, the growing point dies and no flowers will form.

Boron deficiency in tung

Symptoms of boron deficiency in tung first appear on the petioles of the young developing leaves as dark green rings, which later become ridges. The young leaves are light green and glossy and the interveinal tissue expands more rapidly than the veins giving the leaves a “puffy” appearance. The leaf veins may crack and become suberized, internodes are short, and terminal and lateral growth stops.