Contents
- Tree morphology and more
- Flower and Pollination
- Cultivation description
- Planting Design, Training, Pruning
- Propagation
- Harvest and postharvest handling
- General phenology
- Fertilization
- Tissue analysis
Tree morphology and more
Tree - Small to medium sized tree with a spreading, open canopy, usually 4-5 meters in commercial orchards. The tree can live up to 50 years when irrigated and 20-25 in non-irrigated orchard.
Leaves are linear or slightly ovate, about 3-4 times longer than wide, with acute tips and finely serrate margins. Leaves are 7.5-12.5 cm in length, slightly smaller and less folded along the midrib than peach leaves.
Flowers are borne laterally on spurs or short lateral branches, or sometimes laterally on long shoots as in peach, particularly in younger trees. Flowering on basal spurs of 4-6 yr old wood gradually declines, since terminals fail to grow out when many flowers per spur set fruit; hence older limbs become unfruitful and are pruned out. Flower buds are identified as rounded shape while the vegetative ones have a sharp shape. The determination between the two is done during summer time.
Root - Big root system, one major root and secondary horizontal system that will stay shallow in heavy soil (60 cm) and deeper in light soils. The almond's roots have high sensitivity to water logging.
Fruit - A nut. The entire fruit including the hull is a drupe; however, the hull dries and splits prior to harvest, revealing what appears to be the pit of the fruit. Botanically, this pit with the kernel inside fits the definition of a nut (dry, indehiscent fruit with a hard shell). Fruiting begins at 3-4 years old trees, with maximal production in 6-10 years; almond trees can produce more than 50 years. Thinning is unnecessary, poor setting will be referred as 20%, average as 30-40% and very good as 60% (affected by internal nutrient balance); a high proportion of flowers must set fruit for normal cropping. Fruit setting will not occur in temperatures below 12 c°, high wind speed.
The fruit growth has two stages:
- Very intensive growth that follows the flower fertilization. Very intensive growth that follows the flower fertilization. Very intensive growth that follows the flower fertilization. (Starts 15-20 days after the peak of the flowering and continues eight more weeks).
- Stoppage of the outer part growing and intensive development of the seed.
Fruits can drop due to the following reasons:
- Insufficient chilling – disordered awakening and degenerate flowers.
- Frost damages.
- Bad weather which interrupts insect and bee pollination.
Flower and Pollination
Flowering time has a great importance, due to the incidence of three factors: pollination, rains and frosts. Flowering last an average of 25-28 days within a range of 15-40 days.
Almonds are self-incompatible and require cross-pollination. A few self-fertile cultivar are available, but are generally inferior in quality. Pollinators (honey bees) are absolutely essential, especially since the cool wet weather can occur at relatively early blooming period.
Pollinators are generally planted in separate rows so nuts can be shaken and harvested a row at a time without mixing different cultivars. Since pollination is so critical to fruit set and yield, in some cases two pollinators are used, one blooming slightly ahead (but overlapping) of the main cultivar, and one slightly after.
Indirectly almonds are affected by the bees' behavior, which is related to temperature, winds and rain. Optimum temperature of 25-26 c°, winds below 20 kmh with no rain. For pollination it is common to lay 5 beehives for every ha.
Cultivation description
General conditions
Temperatures - Fruit tree of warm zones. The almond is a true Mediterranean tree, requiring mild winters, and long, rain-less, hot summers with low humidity. Almonds have minimal requirements of chilling hours (200-600). Frost hardiness is -2.2C°, temperatures as low as –0.5 C° may kill young trees.
Rain - Rainfall is harmful any time during the growth and blooming periods. Rain decreases bee activity and therefore fruit set; during fruit development it causes fungal and bacterial diseases; prior to harvest it can cause brown rot or Rhizopus rot of fruits as shucks split. Almonds are highly tolerant to drought, with minimal water requirements (minimum 300 mm), but 600 mm is preferred for better production.
Frost – appears as inner darkening and followed by the fruit drop. The damage is more severe in the lower parts of the tree.
The dormant buds will be damaged only at –25 c°
The “pink” stage at –6 c°
The flowering is damaged at –2 c°
Young buds already beneath 0 c°
Soil - It prefers loose and sandy grounds. In high clayish soils it will be susceptible to soil born diseases. Almonds produce best on deep, loamy, well-drained soils, but will tolerate poor soils as long as the soil is not too wet, or poorly drained.
Salinity – the sensitivity threshold is 1.5 mS/cm, at 2.0 mS/cm 10% yield deterioration, at 2.8 mS/cm 25% yield deterioration and at 4 mS/cm a yield deterioration of 50% is occurring. Maximum chloride concentration possible is 350 ppm. Almonds are sensitive to excessive salts, especially of Na (leaf Na 0.30 % or more) and of Cl (leaf Cl 1.79 % or more).
pH – can grow in a wide range of soil solution pH 5.5 – 8.5.
Planting Design, Training, Pruning
Trees are planted in rectangular or hexagonal arrangements, with separate rows of pollinators and main cultivars, usually alternating with each other (US description). Solid rows of pollinators are used since trees are shake harvested, and this makes it easier to harvest without mixing cultivars. In some orchards, two different pollinators are used, generally one blooming slightly before and the other slightly after the main cultivar. The spacing must be wide enough to permit movement of harvesting equipment, or about 5.5 meters.
Trees are trained to an open center shape in the first year (USA). Young trees are headed at 1 m to allow adequate room for trunk shaker attachment. Three scaffolds are selected initially, about 7-14 cm apart from each other on the trunk, spaced equidistant when viewed from above. Various degrees of pruning are practiced after the first year, with minimal pruning allowing the most rapid production of bearing area. In subsequent years, scaffolds are trained to fill their allotted spaces in the tree.
At maturity, pruning consists of water-sprout removal, removal of dead and interfering branches, and limb thinning. Little pruning is needed since so many fruiting points are needed for cropping, and vigor is low in mature trees. Since fruiting spurs live about 5 years, fruiting wood should be renewed every 5 years, or, 20% of the canopy should be pruned back each year to allow new wood to grow and replace the old. In practice, trees can be pruned every other year with no loss of productivity. Under proper management, trees should have many 38-50 cm long 1-yr-old shoots. These shoots will branch, grow spurs, and become fruiting wood in subsequent years.
Propagation
Almonds are budded onto seedling rootstocks so that the integrity of the cultivar is kept intact. Propagation of trees from seed is possible, and practiced in some regions of the Mediterranean. However, tree uniformity is poor in seedling orchards since almonds are self-incompatible and heterozygous as a species. Almonds root poorly from cuttings.
- Peach seedling stock trees - are more vigorous and bear earlier than those on almond seedling stocks. Peaches are slightly more tolerant of crown gall, verticillium, oak root rot and Phytophthora than almond.
- Almond seedlings - are used as rootstocks in less-intensive orchards, where soils are calcareous and irrigation is not available. These trees may tolerate drought better than trees on peach.
- Peach x Almond hybrids - are recent introductions, these stocks having similar disease response as almond seedlings, but some have been produced with resistance to root-knot nematode and iron deficiency.
Harvest and postharvest handling
Maturity
The hull splits at maturity, and nuts physically separate from the tree at this point. Trees are harvested when hulls of fruit in the interior of the canopy are open, since these split last. The seed coat turns brown during the drying-out process of maturation. Delay in harvest increases risk of navel orange-worm infestation.
Harvest Method (USA)
Mechanical tree shakers harvest trees. Young trees may be damaged by shakers, so are harvested by hand knocking in the first few years. Hand knocking is used in production regions that lack mechanization or are too hilly to accommodate shakers. Nuts are then left to dry on the ground for 1-2 weeks, and then swept into windrows for harvesting. In situations where rain, higher humidity, or pest pressure necessitates, nuts are shaken and taken immediately to a processing facility. A mechanical harvester then picks up the windrowed nuts, blowing off extraneous leaves and debris.
Postharvest Handling
Fruits may be dried and hulled immediately, or stockpiled for fumigation against Navel Orange-worm after harvest. Nuts are dried by forcing hot air until their moisture content reaches 5-7%. Nuts are then de-hulled and shelled. The hulls are often sold for livestock feed. In-shell nuts can be stored in bins for weeks or months until final processing. Nuts are then shelled and sorted for size and appearance. Last, nuts are bleached for color improvement, then salted, roasted, and/or flavored.
General phenology
Dormancy - Almond is a deciduous tree. The trees are getting dormant during the autumn and defoliate its leaves. The dormancy period can arrive earlier if aphids attack the tree, water stress or low temperatures. Dormancy is preferred as the temperatures are going down and not before this to assure the trees will enjoy longer period of carbohydrates accumulation within their branches.
Early flowering – During the autumn if the right conditions are created (day length, temperature and soil moisture) part of the buds can wake up. This is an undesired situation because of the waste of some of the spring buds, waste of tree’s energy and the possibility of a disease transfer through leaves that do not defoliate during the winter.
Alternated bearing- Almonds have a certain alternated bearing, not as strong as olive.
Juvenility - last 2-4 years depends on treatment. Pruning is delaying the fertility and the tree will keep on vegetative growth.
Bitter and sweet almonds – the taste is related to expression of recessive genes that forms a glycoside called Amigdalin. The Amigdalin form HCN (toxic cyanide).
Fertilization
Mature bearing trees:
Nitrogen – In almond trees, nitrogen is needed to renew and invigorate fruiting wood. Also, it is needed for fruit growth and development. The greatest need for nitrogen occurs when the almond trees came into production. At this time, the demand for nitrogen is due to fruit development, foliage formation and tree storage in roots and branches. We must meet the tree demand for nitrogen, since a shortage of this element can reduce yields.
Most of the nitrogen applied to an almond orchard becomes part of the kernel, hull and shell. Therefore, the projected yield of the orchard can be used to estimate the need to replace nitrogen removed in the crop. Apply approximately 33 gr of nitrogen for each 326 gr of projected Kernel (meat) yield.
Over-fertilization can lead to excessive vegetative growth, which can create shading for fruiting wood. Furthermore, over-fertilization will increase production costs and will lead to water contamination.
Maximize Efficiency:
- Apply N only when leaves are present and the tree roots are active.
- Apply a uniform irrigation that is adequate to carry the N into but not past the root zone.
- At young nonbearing trees apply nitrogen as long as irrigation continues.
- Mature trees need most of the N in early spring, therefore, a late summer application of part of the N before an irrigation will provide the tree with N for early spring growth. The rest of the N needed should be applied during the spring.
- Fertigation is very efficient in N applications.
- Analyze leaves to fine tune N level to the orchard. Maintain the level in the adequate range. Application reaches 200-250 kg of N/ha. Post harvest application of 50 kg/ha is also recommended. 2.5 -3.0 % out of D.M in tissue analysis.
Potassium – Almond kernels contain 0.75% K (USDA data); and potassium represents more than 2% of the dry weight of almond hulls (Calixto, 1982). Among soil-derived nutrients, potassium and nitrogen are removed in the greatest quantities. Leaf analyses are usually performed on leaves sampled when nutrient concentration is relatively stable. However, analysis this late in the growing season allows the grower plenty of hindsight, but scant opportunity to correct deficiencies.
Application of 250 kg of K (elemental), 1.4% out of D.M in tissue analysis.
Haifa Suggestion for efficient K fertilization: Haifa Bonus™
Phosphorus – application will follow according to tissue analysis.
Foliar Nutrition - It is recommended to spray:
- 1% Poly-Feed™ 20-20-20 or 23-7-23 or 21-21-21 foliar nutrition in 3 cycles during fruit set. First spray should be applied after flower petal fall and two additional with an interval of 7-10 days between application. These foliar applications corrects transient nutrient deficiencies due to strong temporal demand for macronutrients and possible weak uptake by roots in the early spring time.
- 2%-4% Haifa Bonus 13-2-44 during kernels filling, two sprays with an interval of 7-10 days.
Boron - 2 kg/ha B when deficiency occurs. Boron deficiency may be a problem in any orchard on sandy soils and/or where irrigation water is low in B, causes the following problems:
- Low nut set
- Excessive nut drop
- Malformed nuts
- Undesirable vegetative growth
Foliar B should be applied al early post harvest, which is more effective than spring or dormant sprays. Sprays at hull split may also be effective, but have not been sufficiently tested. In California, B toxicity (leaf B 87 ppm or more) and deficiency both present problems.
Zinc - Zn deficiency is controlled with sprays of 19-29 g ZnSO4/l in the dormant period and by foliar sprays of 6 g ZnO/l applied in mid-season.
Young non-bearing trees:
Better to be followed by N and K at the same ratio for better uptake of nitrogen.
First year – 100 – 150 gr N/tree.
Second year – 200 – 300 gr N/tree.
Third year – 350 – 500 gr N/tree.
Tissue analysis
Macro elements
Microelements
