Origin and production

Pistachio (Pistacia vera L.) is almost certain native to western Asia and Asia Minor. Some botanists speculate that the pistachio trees found in the wild in these regions are in fact escaped from orchards and that P. vera resulted from early selection processes using Pistachia terebinthus L. as starting stock. Via Iran where pistachio has been a well established crop many thousands of years B.C., its cultivation spread in the Mediterranean world. There is reliable archeological evidence that the nuts were already used as food in Turkey as early as 7000 B.C. The pistachio first appeared as crop in Italy early in the first century A.D.; in this case the plants came from Syria, which remains a traditional producer today.

The crop was introduced in California in 1904, however, commercial production in California started in earnest in the late 1970’s, although early attempts were made already in 1929. Although pistachios are also grown in Arizona and New Mexico, these acreages are very small in comparison to the Californian acreage, which was, excluding new plantings, 84,485 ha (208,608 acres) (2009 statistics). The acreages of the other major producers are shown in Table 1.

Some botanical information

The appearance of P.vera is best described as a broad, bushy, deciduous tree with one or several trunks. These are slow growing trees, which can reach a height of 10 m (30 ft). Pistacia is a member of the Anacardaciae. This botanical family includes also the cashew nut, mango, poison ivy, poison oak, pepper tree, smoke tree, and sumac. P. vera is the only one of the twelve species in the genus Pistachia of which the fruit attains a sufficient size to be interesting for commercial production. An other very desirable and unique property of P. vera “nuts” is the formation of its semi-split shell after harvest. Commercially this is major advantage, for it allows roasting and salting without the need to first shell the nuts, while in case of 90% of the pistachios harvested in California are eaten as in-shell snacks. Botanists will point out that the so-called “nuts” are actually drupes, but that everybody will always refer to them as nuts.

Pistachios are dioecious: male and female flowers grow on separate male and female plants. Pollen from the male flowers are carried by wind to the female plants – wind pollination. Thus male trees must be selected that flower and shed their pollen at the same time female trees are receptive. Also, to ensure optimal fertilization, the [male] pollinator trees must be spaced evenly throughout the orchard.

Production

Pistachio trees take approximately seven to ten years to reach significant yields. Production is alternate bearing, meaning the harvest is heavier in alternate years, with wide yield variations between on and off years. As example, the yield in California ranged from 1999 to 2009 from 1,504 kg/ha (1,341 lb/acre) of bearing acreage to 4,085 kg/ha (3,644 lb/ha), with an average 10-year yield of 2,990 kg/ha (2,667 lb/acre). The biennial fluctuations in California are shown for two different 10-year periods (Fig. 1).

Figure 1. Illustration of alternate bearing in California


Sources: CPC, ACP and CASS statistical data

Peak production is reached at approximately 20 years. Pistachios grow in areas of long, hot and dry summers, and moderately cold winters. Sufficient chilling hours below 7.2 oC are necessary to break winter dormancy. Pistachio trees are quite cold hardy and can survive temperatures of -10 oC. The deep-rooting trees do best on soils that are deep, friable and well drained, but moisture retaining. P. vera can, however, survive in poor, stony, calcareous, highly alkaline or slightly acid, or even saline soils.

Production Statistics

Major producing pistachio countries are Iran, the US (predominantly in the State of California), and Turkey (Please also Table 1). Other countries are, in order of importance: Syria, China (data not validated), India, Italy, Greece, Uzbekistan, Tunisia, and Pakistan.

Figure 2. Key Global Pistachio Producers, 2008

Percentage of the global Pistachio nut production


Source: FAOSTATS 2009

The overall production figures should not be viewed in isolation. To obtain a picture of the ultimate success with which the various countries grow pistachios, it is necessary to look at the yield per hectare (acre); please see table 2. The highest average yield is achieved in California, while Iran which currently leads with the highest global production, has an average yield per ha of 686 kg/ha (612 lb/ha). Iranian sources are concerned that they will not be able to maintain their position as the biggest global producer. The outputs continue to decrease; the prediction is that this year’s production will drop down to 150,000 MT. The fear in Iran is that they will permanently lose their top position due to water shortages, antiquated cultivation methods and lack of investment.

During the period from 1995 to 2008, acreages harvested increased in all key producing countries: 102% in Iran, 133% in Syria, and 55% in Turkey. The acreages harvested in these countries in 2008 are listed in Table 1. The growth in acreage for California is demonstrated in Fig. 3. It should also be mentioned that the acreage of annual new plantings in California increased over the past 15 years four-fold, from 3,413 to 12,128 newly planted acres/year (1,381 ha to 4,908 ha/year). It is to be expected that the USA will become the leading global pistachio grower within the next five years.

Figure 3. Pistachio Acreage California, 1995 – 2009

Bearing trees and total (excluding new plantings)


Sources: CPC, ACP and CASS statistical data

Importance of Potassium in Pistachio

Potassium Fertilization

Essential for high yields and quality nuts. As mentioned earlier, pistachios are characterized by alternate bearing. This has a major effect on K uptake. In high production years, trees with a heavy crop load, can absorb more than 2 times as much K as off year trees. Most of the potassium uptake occurs during the nut fill period. Little K uptake occurs at the spring flush or postharvest periods. This high K uptake during nut fill maybe related to carbohydrate transport and storage in the fruits. Thus, it is important that supply of soil K is adequate during this time to ensure high yields.

Fruits and leaves remove significant amounts of potassium, accounting for over half of the K in a mature pistachio tree during the on year.

Trial Results

In a field experiment by the University of California, Davis, potassium was applied at four rates (0, 110, 220 and 330 kg ha^-1), as potassium sulfate, potassium chloride, or potassium nitrate. During the spring flush leaf K concentration was low. This may be due to rapid leaf expansion and increase in leaf mass. As fruits developed leaf K increased dramatically which is atypical of perennial fruit crops. After harvest, leaf K declined rapidly, with K most likely being translocated to other tree parts like limbs and trunk.

Field results also show that, applications of potassium, as potassium sulfate (or other potassium sources) above and beyond 220 kg ha^-1, tended to decrease nut yield. The reasons for this decline maybe associated with decreased calcium and magnesium leaf concentrations. There is a well documented antagonism between K and Ca and Mg. High potassium inputs may induce calcium and magnesium deficiencies in citrus and deciduous tree crops. The researchers report that at high concentrations of K there was a reduction in leaf Ca and Mg concentrations.

Potassium fertilization at rates of 110-220 kg ha^-1 had a significant effect on nut yield and quality.

An increase in split nuts is a very desirable quality as pistachios are marketed in-shell and opened by hand by consumers.

Benefits of K Fertilization

The benefits of Potassium fertilization in pistachios

The field studies discussed in the previous section demonstrate convincingly the benefits of a well managed K fertilization program. In summary these are:

• Increased nut quality
• Increased yields
• Higher 100-nut weight
• Larger percentage of split nuts
• Fewer blank nuts
• Improved nut filling
• Decreased susceptibility to fungal infections by Alternaria that cause stained nuts
• Contributes to the overall health of the tree
• Improves water use through regulation of photosynthesis and transpiration
• Lower salt index minimizes crop damage due to soil salt build-up
• Low chloride decreases potential chloride toxicity due to accumulation in the plant tissue