Agriportal

 The top four horticultural crops in Diyala, reportedly in order of importance, are grapes, pomegranates, citrus, and dates. The outline below mainly provides information on table grape best management practices. In a few instances, differences in the cultural requirements of table and wine grape are noted. The sections covering pomegranates, citrus and dates have yet to be developed.

I. Grapes

A. Site selection

Factors include cost, proximity to markets, labor supply, and availability of water

B. Select grape cultivars

1.      The planting of different table grape cultivars that mature at different times will allow the farmer to spread the harvest over several weeks.

2.      Where possible, select grape cultivar that is least susceptible to diseases. No grape cultivar, however, is entirely disease resistant.

3.      Halwani Lebanon and Kamali cultivars are said to be the most important seeded table grapes grown in Iraq. Other cultivars are grown in Iraq and should be considered.

C. Field layout and land preparation

1.      Map the field and plan the row direction and spacing. Good air circulation is important to reduce disease and the layout should be planned to make spraying and harvesting easy. Usually, vines are planted in rows oriented north and south to allow the most sun onto vines. If there is a slope, if possible set the rows across the slope to reduce soil erosion.

2.      If the field is not well drained or a high water table exists, consider installing tile or surface drainage, or both as required.

3.      Control weeds, particularly perennial ones.

4.      If possible, have a soil analysis done to determine the native fertility level (phosphorus, potassium, calcium, magnesium). Add the appropriate amounts of nutrients recommended by the soil testing service. Liming is needed if the soil pH is below 5.5; add lime to bring the soil pH to a range between 5.6 to 6.8) before planting. Acid-tolerant grape varieties can tolerate soil pH levels to about 5.0 (http://www.nysaes.cornell.edu/hort/faculty/pool/GrapePagesIndex.html).

5.      Add manure or other organic matter if available to improve the soil nutrient levels, tilt and structure. Consider planting and tilling in a green manure or cover crop prior to planting the vines.

6.      Thorough land preparation is essential before planting. Subsoil if a hardpan exists and if possible, plow to a depth of 25 to 30 cm, crumble the clods, and level low areas.

D. How to avoid soil erosion and poor soil structure?

1.      Annual cover crops - seed a cover crop such as Italian ryegrass in August and till it under the following May. Soil is protected during the winter which reduces erosion.

2.      Semi-permanent cover crops - seed perennial grasses and leave them for two or three seasons before tilling under. Some growers till alternate rows of cover crops each year. This method keeps soil covered for longer periods of time which reduces erosion still further.

3.      Permanent cover crops - seed perennial grasses. This effectively reduces soil erosion but will compete with the grapes. Pay particular attention to nutrients and weed control when using this alternative. Some growers use a sod cover in alternate alley ways and an annual cover crop like oilseed radish in the others.

E. Soil Structure and Compaction

1.      Grapes, like all crops, need a good root system to be productive. Soil with good structure provides a suitable area for growing roots. Grape roots can penetrate to depths of 3 to 4 m (10 to 12 feet) if the soil has good structure and is well-drained. Soil structure and compaction can be improved by attention to the following practices.

2.      Replace or build the level of organic matter in soil by using cover crops, manure or organic mulches. (Any organic, off-farm waste requires a permit from Ministry of the Environment.)

3.      Reduce the amount of cultivation or use permanent grass cover crops.

4.      Reduce the number of trips over a field. Combine jobs where possible.

5.      Stay off wet soils as much as possible.

6.      Reduce the weight of equipment.

7.      Use deep-rooted cover crops. Subsoil where necessary at the depth of a compacted layer. Subsoil every two or three years only on dry soils and alternate row middles if possible.

F. Planting date (May-June/Feb)

Early spring is the best time to plant grapevines. Fall planting is not recommended because plants are likely to be lost to frost heaving during the first winter. During the first year, the soil is prepared for planting, cultivars are selected and vines are planted, mulched, fertilized and kept free of weeds, insects and diseases. Prune off broken or dead portions of branches and roots. At the same time, prune top growth to a single cane. During the first year, tie the vines to a stake to keep them off the ground, prevent damage and make spraying more effective. If the first season is dry, supplemental watering may be necessary to keep the vines growing. It is important to get as much first-year growth as possible.

G. Plant configuration (spacing) and depth of planting (Y. type trellis, 3.5 x 1.5 m)

1.      The general recommendation is to plant vines at the same depth as they were in the nursery. A planting depth of 120 cm in Iran produced the best yields of Thompson seedless grapes under rain-fed conditions.

2.      Headland space should allow for equipment to move and turn at the ends of the fields.

3.      Access aisle allowance is determined by the row length and equipment used. Shorter rows make transport from the middle of the field less of a problem.

4.      Vine spacing x row spacing typically is 2.4 to 2.7 X 3.4 to 3.7 meters. Vines planted for training on a trellis are normally placed 2.7 m (8 feet) apart, while those planted for training on an arbor can be placed 1.4 m (4 feet) apart. Before growth begins the second year, a support for the vines--either a trellis or an arbor--must be provided.

5.      Three years are normally required to establish a grape planting. Care of vines the second year is similar to that of the first year. A system for training the vines should be selected during the second year. Vines are trained to a particular system by pruning and tying the canes to the support system.

·         In some methods of training grapevines, the canes are tied to wires above the trunk and arms of the vines. Such training works well where grapevines are to be grown on a fence or in an upright position.

·         In another method of training, the canes are tied to the wires and the fruit bearing shoots are allowed to droop or hang down.

·         A third method is the cordon type training system. Here the fruiting canes are developed from a horizontal extension of the trunk called a cordon. If canes are pruned long, they can be tied to the lower wires. If pruned short, they hang free. One of the most common training systems is called the single curtain/cordon bilateral system.

·         Annual pruning is important in maintaining a uniform yearly production of quality fruit. The best time to prune grapevines is in the dormant season after all danger of severe cold weather. Learning to prune grapevines requires practice and experience.

H. Nutrient Management

1.      To manage nutrients effectively, test petiole and soil samples in combination with visual assessment and common sense. Petiole analysis is the most effective practice. Sampling is done in the first two weeks of September.

2.      Post-emergence fertilizer application method and amount

·         By fertigation (the application of nutrients through irrigation systems): 200 kg nitrogen per hectare, 350 kg of potassium oxide/ha, and 60 liters of phosphate/ha

·         In established vineyards, usually only nitrogen and potassium additions are needed. Nitrogen can be applied in the form of manure or as inorganic nitrogen. Potassium comes from applications of muriate of potash. For the best results, band fertilizer on grape rows. Do not automatically apply fertilizer every year; petiole analysis will show needs. To prevent leaching and run-off, apply fertilizer in the late spring.

3.      Keep records of soil and petiole analysis, visual assessment of vine health, yields and weather conditions. These records and your own experience will help interpret problems and results from year to year.

I. Water management and irrigation schedule

1.      Grapes can be irrigated by flooding or with sprinkler or drip irrigation. Factors influencing the choice of system include water quantity and quality and costs of installation and management. Drip irrigation makes the most efficient use of water but is the most expensive to install.

2.      Irrigation frequency is determined by water holding capacity of the soil and stage of growth. An adequate water supply is most important during the growth of vines and berries. For table grapes, water stress should be avoided during berry growth.

3.      Good water drainage is important for a healthy root system. Poor drainage which allows water to stand on or saturate soil increases frost-heaving damage to grape roots and trellises.

4.      Use irrigation with care, particularly when growing wine grapes, as it will affect the quality of the fruit and delay wood maturity.

J. Monitoring for diseases (The berry moth Lobesia botrana)

Common grape diseases are black rot, downy mildew, powdery mildew, phomopsis cane and leaf spot and botrytis bunch rot or gray rot. Significant insect and mite pests on grapes are grape berry moth, Japanese beetle, grape flea beetle, European red mite, grape root borer and grape phylloxera.

1.      Many of the points outlined in this section are preventive. Monitoring pests, using equipment in good repair on healthy vines, on well-maintained trellises and careful spraying will reduce problems.

2.      Chemical pest control may be complemented by appropriate practices and cultural methods.

L. Cultural Practices

1. Select varieties that resist disease where possible.
2. Choose a system of training that allows light, air and sprays to penetrate.
3. Use good sanitation practices such as: tagging and removing vines with Crown-Gall, Eutypa dieback, or infections; removing diseased wood from the vineyard; chopping pruned wood finely and working into soil when vines are healthy; keeping row areas weed-free; and clearing wild grapes from fence rows and surrounding fields.
4. Use canopy management, to improve air movement, water evaporation and the penetration of light onto vines.
5. Keep trellises in good repair. Monitor pest populations in each section of the vineyard.

M. Chemical Control

1. Read and follow the label carefully.
2. Use sprayers equipped with curtains to reduce drift.
3. Calibrate equipment regularly.
4. When possible, use directed sprays. For example, while the whole vine must be sprayed for black rot, only fruit needs spray for Botrytis.
5. If sampling shows that only outer vines have insects, use a perimeter spray. Pay particular attention to the edges of wooded areas.
6. Follow the strategies recommended for each pest. Alternate spray materials to reduce the chance a pest will become resistant.

N. To control weeds under grapevines, consider:

1. A herbicide strip.
2. Mulches.
3. Grape hoe - use the hoe during the early spring to reduce herbicide use. Herbicides should be applied after the final hill is in place.
4. Pre-emergence herbicide (Trufluralin, Treflan) can be used to control germinating weeds.
5. Post-emergence herbicide (Basta, Round-up for mature vineyards only)

O. During the third season, some harvest may be expected from the vines. The first full crop, however, will not be produced until about the fourth or fifth year.

P. Harvesting date (beginning of June)

Q. Storage (for one month at 0°C)

R. SUMMARY:Selecting disease tolerant cultivars, good sanitation practices, managing vine canopies for good air movement, pest scouting and an effective spray program are all part of a successful pest management program.

S. Additional Resources

1. Pruning, Training, and Grape Canopy Management: http://viticulture.hort.iastate.edu/info/pdf/prunecanopy.pdf
2. Grape Leafhoppers: http://cru.cahe.wsu.edu/CEPublications/eb1828/eb1828.html
3. USAID Grape Variety Benchmarking Project: http://pdf.usaid.gov/pdf_docs/PDACG128.pdf
4. Midwest Grape Production Guide http://ohioline.osu.edu/b919/0007.html
5. Cornell Grape Pages (an excellent discussion on soils and nutrient management: http://www.nysaes.cornell.edu/hort/faculty/pool/GrapePagesIndex.html
6. California, Tulare County: http://cetulare.ucdavis.edu/pubgrape/pubgrape.htm#Table

B.  Best Management Practices for Citrus

Climatic requirements

• Citrus trees are subtropical in origin and cannot tolerate severe frosts. 
• Moisture is also a limiting factor in citrus production, When rainfall is  poorly distributed and, it is necessary to supplement moisture by irrigation to ensure that moisture stress do not suppress growth and production.
• Citrus (except lemons) require shorter days and cooler temperatures in winter for a normal production rhythm.
• Flowering should occur almost exclusively in spring, and these spring flowers should produce a large fruit crop 7 to 12 months later, depending on the cultivar.

Soil requirements

• Citrus trees grow in almost any soil that is well-drained, sufficiently aerated and allows tap root to penetrate to the desired depth.
• Citrus can be grown in a wide range of soil types provided they are well drained. Fertile, well-aerated soils with a pH of between 6 and 6,5 are ideal.
• The growth, development and production of a plant depend on the physical characteristics of the soil such as drainage, density, texture, water-holding capacity, structure, soil depth, the homogeneity of the profile, erodibility, and the degree to which water can infiltrate the soil. These characteristics differ in the various soil types.
• Physical soil properties determine the degree in which water is released for uptake by the plant roots, and the depth of the root system.

Root development

• The roots of citrus trees normally grow to a depth of 1 m and spread to 2 m beyond the drip line of the tree.
• Certain factors, such as a rock or gravel layer, a mottled clayey soil or a sandy mottled layer could, however, limit the normal spread of the roots.
• If any limiting layers are found within 1 m of the soil surface, the effective soil depth for the development of plant roots will be restricted to the depth at which the upper boundary of the restrictive layer occurs. A greater effective depth will cause an increase in plant yield and growth, because a greater volume of soil can be exploited by plant roots.  Root development can also be restricted by a low availability of water and nutrients.
• An ideal citrus soil will, in respect of optimum water provision, have the following characteristics: Red, yellow-brown or brown color, Clayey content of 10 to 40 % , No clayey, mottled or structural layers within 1 m of the soil surface.

Lay-out of citrus orchards

• Before planting an orchard it is advisable to provide irrigation facilities such as pipelines or concrete canals. At present the dragline sprinkler irrigation system and the basin system for flood irrigation are regarded as the most suitable for citrus orchards.
• The square and rectangular planting systems applicable to citrus orchards with the exception of the square system which is preferable where sprinkler irrigation is used, the rectangular system is at present favored above other systems because the smaller planting distance in the tree rows increases the number of trees per hectare.

Planting

• Early spring is the best time for transplanting. Planting holes of 0,5 x 0,5 x 0,5 m are prepared and the soil mixed well with 2 spadefuls of compost or manure and 250 g of superphosphate.
• The young trees are planted to the same depth as they were in the nursery. Keep in mind that loose soil tends to compact. The bud union should be about 300 mm above the ground.
• Once the tree has been planted, the soil must be firmly tramped down. A basin for irrigation is made around the tree which must be thoroughly irrigated immediately after planting. Irrigate again the following day to seal any cracks in the soil.

Schematic illustration of the square planting system

Schematic illustration of the rectangular planting system

                    Planting depth for citrus tree

Irrigation

During the first 6 months the trees should be irrigated twice a week and thereafter every 7 days. The irrigation basin should be gradually enlarged as the tree grows, so that it is always slightly bigger than the drip line of the tree. Be careful not to damage the fine superficial feeder roots. The water required depends on weather conditions. Saturated and poorly-drained conditions could result in root rot, which will shorten the life of the trees. On the other hand, a shortage of water may have the following effects:

• Moisture stress during early spring while the tree is flowering, could result in excessive drop of flowers and fruitlets, and the resulting crop will be small. A serious drought followed by good rains could produce out-of-season flowering and fruit setting.
• A lack of moisture during October to January could result in acid fruit.

If a sprinkler is used, about 30 mm of water must be applied every 7 days, depending on the weather.

Fertilization

During the first year, nitrogen may be applied every 2 months. Any of the following nitrogen fertilizers may be applied:

• 6 applications of 25 g limestone ammonium nitrate (LAN 28 %) per tree per year OR
• 6 applications of 16 g urea (46 %) per tree per year OR
• 6 applications of 36 g ammonium sulphate (21 %) per tree per year (one matchbox full of fertilizer is roughly 36 g).

From the second year, nitrogen must be applied twice a year, half in July and half in March. Fertilizer should be spread evenly under the canopy of the tree and irrigated. Very deep irrigations will wash the fertilizer down too deeply and out of reach of the shallow feeder roots.

Phosphorus may be applied at any time of the year. One application should be sufficient. Potassium should also be applied once, early in spring. It is often necessary to apply micronutrients. These elements are dissolved in water and applied as a spray onto the tree. Deficiencies of zinc, copper and manganese often occur and may be applied in 10 l water at the following concentrations:

• 15 g zinc oxide
• 20 g copper oxychloride
• 20 g manganese sulphate.

The micronutrient solutions should be sprayed during early spring when the leaves are actively growing. A boron deficiency can be rectified by spreading 20 g borax per large tree under the canopy or by spraying with a solution of 10 g solubor/10 l water.

The table indicates how the fertilizer requirements of growing citrus trees increase.

Fertilizer requirements of young citrus trees (kg/tree/year)

Pruning

• Citrus trees are not usually pruned, although dead wood must be removed regularly.
• To avoid low branches touching the ground, trees are skirted soon after the crop is removed.
• Branches touching the ground hamper the removal of fruit lying underneath the tree, impede irrigation and promote ant infestation of the trees.
• When trees become too big and start growing into one another, pruning is recommended.

Frost Control

Protection from frost is critical. Most citrus will freeze when fruit temperature drops to 27-28°F. The main methods of frost protection are by wind and water. Wind machines -- large fans on poles about fifty feet above the grove -- are turned on when the temperatures near freezing. The fans mix the slightly warmer air above the grove with the colder air near the ground, which warms the air around the tree. By applying water, the heat built up in the soil during the day is lost more slowly, and air temperatures around the fruit stay warm a little longer. A few growers still use oil-burning orchard heaters, but this once common method is seldom used now because of the cost.

Pests, diseases and control

Pests: Ants, Red scale, Soft brown scale, Citrus thrips, Orange dog, Citrus psylla,  Fruit flies, whitefly, False codling moth,  Citrus bud mite, aphids.

Diseases:  Citrus black spot, Scab , Greening, Citrus root nematode

• Control: To keep ants out of the trees, insecticides sold under various trade names can be applied around the tree trunks. As greening is usually localized within one or two branches of the tree, it is advisable to cut out such branches. Saw them off as close to the trunk as possible. If the entire tree is affected, it would be better to remove and replace it.

Management

• Leaving the crop on, after the next crop has set, may reduce the yield of the subsequent crop and thereby may induce the rhythm of alternate bearing
• Thinning of fruits in the 'on' year was also suggested to overcome alternate bearing in citrus; chemicals like NAA are recommended.
• Adoption of the practice of thinning to secure regular crops in citrus is not reliable.
• One undesirable feature of the alternate bearing pattern is the inferior size of the fruits during the ‘on’ year.
• Thinning leads to an increase in average size of the fruit.
• During ‘on years the crop loads are so heavy that major tree branches are broken.
• Trees in a single orchard as well as a single district tend to become synchronized in their alternate bearing, resulting in marketing troubles.

References

www.nda.agric.za/publications,  www.sunkist.com/products/how_citrus_trees.asp

www.ehow.com/how_3642_prune-citrus-tree.html, www.treehelp.com/trees/citrus/care.asp

C.  Best Management Practices of Pomegranate

1-  CLIMATE

The best quality pomegranate fruits are produced in regions with cool winters and hot, dry summers. Pomegranates vary in frost tolerance, but in some cases temperatures down to 10°F may not severely injure the plants. The recommended site must comply with the growing conditions:

• Dry weather, particularly during fall.
• Sandy soil or other with good drainage.
• Water availability of 3.5 mm/day by drip irrigation including the use of treated or salty water.
• Temperature: at summer between 30°C - 44°C and during winter need several days below 17°C (and higher than -5°C).

2-   PROPAGATION

Trees are easily propagated with winter hardwood cuttings, 6-8 inches (15-20 cm) in length and pencil size or larger in diameter. Cuttings should be taken in February or March. The cuttings are planted vertically in open ground 6 to 8 inches apart in nursery rows, with about 2 to 3 inches of the top exposed. It is not necessary to callus the cutting to insure rooting. The plant is allowed to grow for one season in the nursery and then transplanted bare root to the orchard the next winter or early spring. Seed-propagated plants do not grow true-to-type, but seeds will germinate in 45-60 days. Layering is also successful but more labor-intensive.

3-   SOILS

Pomegranates produce best on deep, heavy loams, but are adapted to many soil types from pure sand to heavy clay. Yields are usually low on sands, while fruit color is poor on clays. Growth on alkaline soils is poor. Optimum growth is associated with deep, fairly heavy, moist soils in the pH range of 5.5-7.0.

4-   PLANTING AND SPACING

Plant trees in early spring (February - March), avoiding late frost. Soil should be loosely worked and not too wet. When used as a hedge, plants are spaced 2-3 m (6-9 ft.) apart. Suckers will fill spaces and produce a compact hedge. Spacing of 5-6 m (15-18 ft.) between plants and rows are used for orchards and similar spacing should be maintained for dooryard trees. Picking and pruning can be a problem under close-planted conditions because workers cannot move freely through the rows.

5-   IRRIGATION

The pomegranate can withstand long periods of drought, although not much fruit is produced under drought conditions. Water requirements for pomegranate are about 125-150 cm (50-60 in.) per year. Trees should be irrigated every 7-10 days in the absence of significant rainfall. Adequate soil moisture must be maintained throughout the growing season particularly as harvest approaches in late summer and early fall to reduce potential fruit splitting. Most orchards are irrigated under the furrow system, but sprinkler and drip irrigation systems are satisfactory if properly designed. Orchards thrive under non-cultivation and semi-non-cultivation berm systems. Weed control is difficult because at present no pre-emergence herbicides are registered for use in pomegranate orchards.

6-   FERTILIZATION

Mature pomegranate trees require from ½ to 1 pound of actual nitrogen per tree per year, which is equivalent to 2-3 kg (4.5-6.5 lb.) of 8-8-8 (or similar) fertilizer in November and March. Young trees should receive about 1 kg (2-2.5 lb.) of a similar fertilizer at the same intervals. Excessive or late applications may delay fruit maturity and reduce color and quality. Some evidence indicates that excessive nitrogen applications cause increased vegetative growth and reduce fruit production. Occasionally, zinc deficiency is evident in trees. This can be corrected by applying zinc sprays during the dormant season or to the foliage in spring and early summer.

7-   INSECT PESTS

One widespread insect pest on pomegranates is the flat mite, Brevipalpus lewisi. This small, light-reddish mite hibernates under flakes of bark on larger tree limbs in foliage in mid to late summer, causing a russeting and checking on mature fruit. One or two sulfur dustings in June or early July offer good mite control.

Omnivorous leaf-roller, Platynola stultana, is another serious pest in many pomegranate orchards. The larvae of this insect are first observed in the tops of trees nesting in shoot terminals in June and July. As fruit begins to ripen, larvae enter in protected locations; under leaves, near the stem, or where two fruits are touching. Larvae also cause channels to appear in the rind where they feed under leaves. After entering the fruit they feed on kernels and pupate at the entry location. The fruit usually rots just inside the entry location. Control is difficult because timing must be exact when larvae are first noticed nesting in the shoots. It is difficult to get good coverage because the larvae plaster leaves together or to fruit, and are thus well protected.

Mealybug may cause damage to pomegranates and also citricola scale, black scale, melon aphid, greenhouse whitefly, katydid and thrips (citrus greenhouse and flower) attack the pomegranate but seldom. Scale insects can be controlled by an application of 3% oil spray during the winter when the leaves are not present.

8-   DISEASES

Pomegranate trees are not affected by any serious disease. The fruit, however, is frequently damaged by heart rot, caused by Alternaria fungus. At least three sprays/year of neutral copper fungicide gives desired control. Removal of old fruit from the tree during pruning may eliminate a potential source of fungus as well as shoot dieback for the following season. The disease seems to affect more fruit if there is much rain in blooming season, thus suggesting that moisture in the bloom increases amount of infection.

Root-knot nematode has been identified in pomegranate roots. Not normally considered a serious pest, it may be responsible for a weakening effect on trees, particularly those planted in sandy areas or areas where the root-knot nematode population is very high. Few insecticides or nematocides are registered for use in pomegranate orchards. Control measures for some of the foregoing pests must follow prescribed methods given under special permits through the local Agricultural Commissioner.

9-   TRAINING AND PRUNING

Trees form the nursery are planted bare root in winter or early spring. The natural growth habit of the pomegranate is to produce many suckers from the base of the tree. If a single truck tree is desired, only one vigorous sucker or the trunk of the original nursery tree should be selected and branches grown from it. Basal suckers should be removed periodically in summer and during dormant pruning to promote growth form the main trunk of the newly planted tree.

Pomegranate trees require a small amount of pruning each winter to maintain shape and good bearing surface. Pruning is important to produce stocky, compact framework in the first 2 years of growth. Cut trees back to 60-75 cm (2-2.5 ft.) at planting and develop three to five symmetrically spaced scaffold limbs by pinching back new shoots, the lowest at least 20-25 cm (8-10 in.) from the ground. Branches should be shortened to 3/5 of their length during the winter following planting. Interfering branches and sprouts should be removed leaving two or three shoots per scaffold branch. In addition, some thinning-out of crowded bearing areas helps produce larger fruit having fewer wind scars.

10-  SPECIAL CONSIDERATIONS

Pomegranate trees are self-fruitful. That is, they can pollinate themselves. Severe fruit drop during the plant's juvenile period (3-5 years) is not uncommon. Fruit drop is aggravated by practices favoring vegetative growth such as over-fertilization and excess irrigation. Avoid putting young trees under conditions of stress. Mature trees tend to hold more fruit that are set than will younger trees.

11-  HARVESTING

Picking begins in August before fruit is fully mature. As fruit approaches maturity on the tree it may split. For commercial handling, picking should be completed as soon as possible after fruit has reached maturity standards. Rain on maturing fruit will cause many to split before they can be picked. For shipment, fruit may be waxed to enhance the appearance; it can be held in cold storage for several weeks without losing market quality. Fruit continues to develop to a darker skin color when held at room temperature, and may last several weeks in decorative arrangements.

References

http://www.juvalle.com/PomegranateFarmBook.pdf

http://fruitsandnuts.ucdavis.edu/crops/pomegranate_factsheet.shtml

http://ressources.ciheam.org/om/pdf/c13/96605638.pdf

https://mail.hawaii.edu/attach/Growing%20Technologies%20Ltd.htm?sid=&mbox=INBOX&charset=escaped_unicode&uid=37252&number=3js&filename=Growing%20Technologies%20Ltd.htm