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Almond : a profitable crop in the Mediterranean area

The growing fruit (it’s a drupe) is similar to a peach until it approaches maturity.

The almond tree is a typically Mediterranean crop, presenting an adaptation plasticity to very different conditions. In this way, it can bear high summer temperatures and cold winter extremes, or survive prolonged periods of drought, and it can be cultivated in very poor soils. Although the productive levels will be as much higher as better the environmental conditions.

Botanical description

Almond, (Prunus dulcis), tree native in Iran and surrounding countries in Central Asia and it has edible seed. It´s a member of the family Rosaceae (order Rosales). Almond is an economically important crop tree grown primarily in Mediterranean climates between 28° and 48° North latitude and between 20° and 40° South latitude. California is the most important area producing nearly 80 percent of the world’s supply. Almond trees can be divided in two different type of varieties: Sweet almond (P. dulcis variety dulcis) and Bitter almond (P. dulcis variety amara). Sweet almonds are consumed as nuts and used in cooking or as a source of almond oil or almond meal. Bitter almonds are used for produce the oil of bitter almonds that is used in the manufacture of flavouring extracts for foods and liqueurs. Almonds may be eaten raw, blanched, or roasted.

Almond trees are deciduous with a hardy dormancy. Typically, size is around 3-4.5 metres (10-15 feet) tall. When the trees flowering produce fragrant, five-petaled, light pink to white flowers from late January to early April in the North Hemisphere. The flowers are self-incompatible and that means require insect pollinators to facilitate cross-pollination with other cultivars.

 The growing fruit (it’s a drupe) is similar to a peach until it approaches maturity. When it ripens, the leathery outer covering, splits open, curls outward, and discharges the pit. Actually, almonds are not true nuts (a type of dry fruit) but rather seeds enclosed in a hard fruit covering.

The sweet almond crop is located in an extensive area in the world. The most important point to consider for the success of the plantation is that we don’t have frosts during flowering.

Bitter and sweet almonds have similar chemical composition. Both types contain between 35 and 55 percent of fixed oil (nonvolatile oil), and both feature the enzyme emulsin, which yields glucose in the presence of water. Bitter almonds have amygdalin, which is present only in trace amounts in sweet almonds, and the oil of bitter almonds contains benzaldehyde and prussic (hydrocyanic) acid. Almonds are high in protein and fat and provide small amounts of iron, calcium, phosphorus, and vitamins A, B and E.

 

Irrigation

Almond tree cultivation in Spain has been carried out in rainfed conditions and under bad environmental conditions. However, in recent years crop management is changing, extending to more areas production with irrigation water. This change has made crop productivity in Spain increase the traditional 150 kg / ha of almond grain to a maximum of 1,500 kg / Ha. In other areas, such as California or Australia, almond tree cultivation has proven extraordinary behaviour in irrigated conditions, reaching average productions of more than 2,000 kg / Ha of almond grain (with maximums of up to 4,000 kg / Ha) with endowment of very high irrigation (over 10.000 m3 / ha and year). These endowments in Spain are not possible, but it doesn’t mean it is necessary to renounce the irrigation of the almond tree. With endowments close to 3,000 to 4,000 m3 / Ha, the almond tree crop has an extremely high response to irrigation satisfactory, as long as it is applied at the right time and optimally.

The development of irrigation strategies with water supply below the optimum is due to the limitation of available water resources, caused by increased water needs in the agriculture and the decrease in rainfall expected by the effects of climate change. A times ago, the ultimate goal of irrigation was the crop maximiza­tion. However, currently other factors such as conservation of resources, profit maximization or respect for the environment have every time major importance. That means that we need to increase the water efficiency.

Although it seems an easy task, irrigation is not. Possibly, it is one of the most complex activities that a grower has to face. In addition to know the characte­rization of the crop and have extensive knowledge of the management of irrigation systems, irrigation requires a detailed study of the soil component that it is difficult due to its great spatial and temporal variability.

 

• Different irrigation systems.

Now we have left, the method that we are going to use to get that water to the plant.

There are three methods of irrigation:

- Surface irrigation.

- Sprinklers irrigation.

- Drip irrigation

 

Surface irrigation. Surface irrigation systems include furrow and border strip systems. Border strip systems that flood the area between tree rows (middles) are more common in almonds, but irrigation is also done using a number of furrows paralleling the tree rows. Determining the application rate and especially the application uniformity of surface irrigation systems is very difficult and is usually done by a professional irrigation system evaluator. A grower can determine how much water is applied during an irrigation set, an important piece of water management information. We need to know for correct calculation.

- Flow rate to the orchard.

- Orchard area irrigated during the set.

- Irrigation set time (duration).

The water efficiency in this system is very low, so in the environment of lack of water it is decreasing although it is still very important in old farms.

 

Sprinklers irrigation. The use of micro sprinklers to irrigate almonds plantations has grown considerably over recent years, because micro sprinklers provide many advantages:

- Irrigation adapted specifically for the plantation; the foliage does not get wet, while at the same time, the wetting zone and irrigation volume can be matched optimally to the tree growth stage. Increasing wetting zone radius as the tree grows is easy and rapid, requiring only another sprinkler between the trees.

- Matching the wetting radius and the area beneath the trees to the growth of tree root surface area, with the aim of increasing water and fertilizer take up efficiency and to help establish and stabilize the tree in the soil.

- Irrigation using a wide range of flow rates, including very low rates (2002 Aqua Smart – Up to 20 liters / hour; 15 liters / hour for the Jet family).

- Irrigation using micro sprinkles overhead for cooling and frost protection up to to about -3º C. Wetting the area helps prevent freezing, which can often cause irreversible damage to the trees.

 

Localizated irrigation. Currently, localized irrigation are mostly implanted in almonds tree. Regarding the systems of surface and spray, localized irrigation is more efficient, it needs less water endowments, providing small amounts of water in some fixed points, with a high frequency. This water supply system allows the formation of land areas (bulbs) in where humidity is always maintained very high soil, which favours the absorption of water and nutrients by the roots. They also have the advantage of being able to apply, through irrigation water, fertilizers, herbicides and phytosanitary products. Among its disadvantage can cite the danger of shutter of the emitters, if the water characteristics of irrigation are not good, and the inability to perform work in the sense perpendicular to the branches, if these are placed on the ground surface. Shutter of the emitters, using drippers of high quality and a good filtration can be avoid.

The localized system in almonds tree is divided in two types of irrigation: micro sprinkler and drip pipes. Micro sprinkler irrigation, the emission of the water is done by small sprinklers in form of fine rain. The micro sprinklers present, compared to conventional sprinklers, a need for lower water pressure (1-2 kg / cm2), a smaller flow (16-200 l / hour) and a very wet radius less (less than 3 m). Within the systems located is the one that manages to wet more land area, providing more water with a lower frequency. In areas of much wind presents difficulties due to lack of uniformity in the distribution of water, likewise, It is the one that produces the highest humidity in the plantation, favoring the incidence of diseases.

The drip irrigation system is the one with the greatest advantages for cultivation of fruit trees, being the one used in practice all of the new plantations.

Laterals pipe usually are made of low density polyethylene, with a diameter between 16-20 mm, thickness less than 2mm and maximum pressures of 2.5 kg / cm2. The drippers are water emitting devices, that bring water slowly to the ground, drop by drop, forming a wet bulb in the ground. They are made of plastic material, they are made of low flow rate (less than 16 l / hour), being those of 2 and 4 l / hour the most used, working pressure is around 1 kg / cm2. Can be punctured or integrated inside the pipeline. If the plantation is sloping Pressure Compensated (PC) drippers are recommended, that allow to maintain a constant flow despite the pressure differences that give along the pipe caused by the land level differences.

Drip irrigation has many advantages:

- The ability to work at low flow rates

- Dripping saves water (a solution for countries where water is scarce, but drip irrigation does have relatively high filtering requirements).

- Maintains a continuous wetted strip along the line of trees

- Optimal method for fertilizing the trees

- Avoids wetting the tree trunk and helps reduce humidity, which prevents rotting, disease and weed growth.

 

Subsurface drip irrigation. The use of subsurface drip irrigation (SDI) is nothing new on a worldwide level. In Israel the practice has been around since the 1960s. SDI has had many diverse uses around the world for a multitude of crops on multiple soil types in various climates.

SDI is a system that provides a low-pressure water source to almonds, and other crops, through buried drip tape or hard tubing with built-in emitters.

Subsurface drip irrigation presents, compared to traditional surface drip irrigation, many advantages:

- Higher yields with significant reduction in water usage.

- Several studies have shown soil evaporation, surface runoff, and deep percolation are greatly reduced or eliminated with SDI.

- The volume of wet soil is bigger.

- The maintenance costs decrease.

- It does not limit the traffic of machinery.

- Less herbicide use is required with SDI as there is less of a weed problem.

- The irrigation equipment is protected against pests and climatic damage.

- We are also able to irrigate during windy conditions.

- Studies have found with SDI runoff into streams is reduced or eliminated, and there is less nutrient and chemical leaching due to deep percolation.

- SDI include design flexibility.

- System longevity in some cases, placing water right where the roots are.

- The ability to irrigate during harvest, and a dry orchard floor helping to prevent surface diseases. Research at Kansas State University found damage to almonds drying on the surface during harvest when irrigation may be required is eliminated with SDI.

The main disadvantage are:

- SDI can have a high initial investment cost compared to some other irrigation systems, but that investment pays off in the end with higher crop yields and less water usage.

- Rodents can cause damage to the system by chewing on it.

- Clogging can be a problem from buildup of minerals and algae. Cleanout valves installed at the end of the tube lines are important to remove blockages and draining the system.

- Root intrusion and pinching off by roots can be another problem, all of which growers cannot see until damage becomes evident in the tree or vegetation around it.

- The lack of visual indicators of proper irrigation performance is a major disadvantage with SDI. It cannot be controlled visually the correct operation of the drippers.

- There is a danger of sealing drippers and breakage of pipes caused by soil roots.

Currently, there are dripper tested available in the market to avoid these problems.

Almonds plantations usually cover a large area with lots of movement of animals, including rodents, birds, small reptiles and sometimes even large wild pigs, which can damage equipment and systems laid out on the ground surface, such as surface drip lines, distribution pipes and often, sprinklers as well. That damage can add up to very large sums. Moreover, in many plantations, there is ever increasing use of agricultural machines at every growing stage, including surface nut harvesting. Burying the dripper lines in the ground makes life easier because the surface is clear for the easy passage of machinery and ongoing work.

During planting, two to four dripper lines are buried to a depth of 10cm to 30cm below the soil surface as appropriate for the soil conditions and the risks at large in the plantation. Those dripper lines wait to be used, beginning in the plantation’s third year. During the first two years, the plantation is irrigated using a surface dripper system. After two years (or three according to tree development), the plantation moves over to irrigation using the buried system. If the variety of trees in the plantation has high water demands, which have a very large spread of roots and high water demands; two to four dripper lines are buried on each side of the row of trees in order to reach full wetting of the soil and to reach irrigation volumes sufficient to achieve optimum tree growth.

Dripper systems, including SDI systems, require a high standard of filtration, collection pipes, line flushing systems and vacuum valves. High standards of regular maintenance, good quality filtering and system monitoring will extend the system’s proper functioning and length of working life.

When laying very long lines in a plantation (500 to 700 meters), the grower must ensure that the minimum pressure reaches 3 bar at the beginning of the line and that line must be a 20 mm pipe with one meter spacing between drippers, working at a flow rate of 1 to 1.1 l/h.

 

Bibliography: 

- Nuevas tendencias en el cultivo del almendro, Xavier Miarnau Prim PhD, IRTA

 Fruit, trees and vines, Elias Fereres PhD, University of Cordoba and IAS-CSIC, Cordoba, Spain.

 Almond irrigation improvement continuum, Larry Schwankl and others, UCCE.

 Manual del almendro, Octavio Arquero y others, Junta de Andalucía.

 Manual para el cultivo del almendro, Baldomero Casado y others, Junta de Andalucía.

 Nuts. Almond, pecan, walnut, macadamia, hazelnut, cashew, NaandanJain a Jain Irrigation company.

 Microsprinkler evaluation exampler, University of California.

 Resutado del riego deficitario en leñososos, Ramón López Urrea, ITAP

 Subsurface Drip Irrigation in almonds, By Larry Schwankl, University of California.