Management Techniques to Grow Saffron
Most crop management techniques, above all planting, weeding, flower picking and separating, are performed by hand all over the world. For this reason, saffron cultivation is painstaking and expensive.
The Saffron Express team is proud to invite you to read this informative article about saffron’s adaption conditions.
Saffron cultivation is generally carried out as a perennial cycle, but an annual crop system is adopted in Navelli, Italy. Perennial crop techniques have highly variable durations from place to place: from 3–4 years in Spain, 6–8 years in India and Greece and up to 12 in Morocco. With the aging of the saffron field, generally after 4–5 years, spice production declines because of increasing competition for water and nutrients, fungal infection due to overcrowding and the reduced size and reproduction capability of bulbs. In a ten-year experiment, researchers observed that bulbs left in the soil without management techniques continue producing daughter bulbs for up to 3–5 years and afterwards they degenerate and are no longer able to reproduce vegetatively. Some researchers reported similar conclusions. Every year in perennial crop techniques, daughter bulbs creep upwards by about 2 cm from the mother bulb, and when they reach the soil surface they must be lifted and replanted.
In Navelli, where annual cultivation represents a strategy to avoid parasite infection, the bulbs are lifted up annually at the beginning of the summer, selected for size (diameter greater than 2.5 cm), and checked for possible defects, such as rot, parasites, viruses, etc., before replanting. This continual selection of the best plants, even in the absence of sexual reproduction, may lead to the conservation of the highest morphological and productive characteristics. In annual cultivation used in Navelli after ploughing, a ridging hoe is used to prepare the “raised beds” about 30 cm from soil level, where 3–4 rows of bulbs, 20–30 cm apart, are placed with the apex in the upward direction. Raised beds allow better drainage of the soil and less effort in management techniques. In the highly humid environment of Navelli, perennial cultivation has been very unsuccessful due to the severe attack of root rot.
Bulb Planting (Methods, Rate and Time) and Harvesting
Before planting, the soil should be completely cleared of weeds, ploughed at a depth of 25–30 cm, and left to rest from a few weeks to the entire winter (Navelli). To avoid fungal infection, bulbs can be disinfected before planting by immersion for around 5 minutes in a benomyl, captan or copper-based solution.
Sowing depth and spacing differ in annual and perennial crops. Sowing in perennial crops is deeper (10–20 cm) and wider spaced (10–15 cm between bulbs and 20–25 between rows) compared with annual crops (8–10 cm depth, 3–8 cm between bulbs and about 15 between rows), but shorter spacing is also used in intensive crop systems. A study have shown that rooting and flowering are not affected by planting depth.
Sowing is commonly carried out by hand. Larger bulb size has a well-documented positive effect on spice production in the same and following years, namely, increasing bulb size leads to a greater number and higher weight of replacement bulbs. In unfavorable experimental site conditions in New Zealand, significant effects of bulb size on flowering were detected only in the second crop season. Generally, 2.5 cm is considered the smallest size below which bulbs need to be placed in a nursery for vegetative reproduction.
No univocal information is available for the most appropriate sowing time. In fact, like many other traditional crops, adopted agricultural techniques depend more on local practices passed on from generation to generation rather than scientific knowledge. Bulbs are sown in the second half of August in central Italy (Navelli), from the second half of June in Spain, between the middle of July and end of August in India, between May and September in Greece and between the end of August and the beginning of September in Iran. In any case, bulb dimensions and sowing time may affect daily flower production but not its duration.
After leaf withering, bulbs are lifted up, generally from May to July, but also in September in Morocco, and kept in jute or hemp bags until planting. The external tunic can be removed, leaving only the interior one. In spring, when bulbs pass to the natural summer rest, leaves can be cut and therefore this is a good moment for weed control.
Saffron cultivation needs to be included in a crop rotation. No definitive information is available on the effect of the previous crop on saffron yield and quality, but traditionally between 3 and 8 years should pass before it is cultivated on the same soil. studies reported that a decrease in stigma production and an increase in weed number have been observed when saffron was cultivated on the same soil. In central Italy, saffron is profitably rotated with legumes and wheat.
The application of about 20–30 tons per ha of organic manure is the most common fertilization practice all over the world, while 40 units of N, 30 units of P2O5 and 40 Units of K2O are applied in Greece. Mature horse and cow manure of about 25–30 t/ha, without any chemical fertilization, determined good results in Navelli. On the contrary, incorporation of organic matter before planting did not improve saffron yields in New Zealand. Studies in Iran found that 25 t/ha of cow manure significantly increased the dried stigma production in a soil with low organic content (0.3% in Organic Carbon), but had no effect in a soil with 1.0% O.C. They also observed that annual distribution of 50 kg/ha of nitrogen increased saffron yields, and that phosphorus and potassium seems unnecessary. An Iranian study reports promising results of applying chemical fertilizer, while, in a three-year experiment in two sites in Iran found contrasting results on nitrogen fertilizer, and no effect was shown by the application of phosphorus. Urea foliar fertilization applied on saffron in winter (from January to March) resulted in a significant increase in flower number in a two-year experiment carried out in Iran.
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Irrigation is not a necessary practice. Water requirements of saffron are low and can be satisfied by the scarce rainfall when cultivated in semi-arid conditions. Even in the Mediterranean environment, saffron is not watered in many cultivated areas. Some authors report up to 3000 m3 flood irrigation per year in Iran and up to 500 m3/ha in Morocco. Experiments carried out in Greece demonstrate that irrigation at the beginning of September resulted in an earlier onset of flowering, while irrigation at the end of September and during October determined an increase in production. Late irrigation could result in a worsening of the quality traits of saffron, especially if watered just before flowering. Certainly, the most crucial moment for irrigation is after summer to awaken the bulbs, but this coincides with autumn rains so, excepting a severe drought season, this may be considered unnecessary.
Weeds are probably the main problem for saffron, since it is unable to compete, above all because of its very low height. Nevertheless, due to the short time between the bulb planting and flowering, severe weed problems start the following spring in perennial cultivation. From flowering, weeds can be left to grow until May and then cut without damaging the crop when the saffron leaves wither.
Weeds are managed by hand in annual crops in Italy, while in perennial crops a good chemical control is generally achieved with 10 kg/ha of Simazine (Gesatop 50%) or Atrazina (Gesaprim 50%). In Iran, broad leaves are controlled with pre-emergence and post-emergence treatments of Sencor (Metribuzin) and narrow leaves with Gallant (Haloxy fopetoxy-ethyl) treatments after flower harvest. Pre-emergence treatments with Sonalan (Ethyl fluralin) are also used. During the summer rest, general herbicides such as Roundup (Glyphosate) or Buster (2,4-D, 2,4-DP) are applied.
Little research has been carried out on indirect weed control methods. Interesting results in reducing weeds with agronomic methods have been obtained with wood chips and sawdust mulch. Experimental trials to control weeds with plastic films as dead mulch are on-going in southern Sicily.
Harvesting and Separating
Gathering saffron flowers requires care and intensive manual labor: the flowers only grow a few centimeters aboveground and, depending on vegetative activity, might be surrounded by several leaves which must not be damaged otherwise daughter bulbs will not be produced. The flowers are harvested manually, generally by family members, by cutting the base of the flower stem with the fingernail. About 350–450-man hours are needed to harvest 1 kg of the spice, corresponding to between 200 000 and 400 000 stigmas, depending on the unitary weight. The saffron flower is highly ephemeral; given its very short life, it should be picked the same day of flowering and placed in baskets. The best practice is to pick the flower early in the morning each day, when the corolla is still closed, thereby preventing the stigmas from losing color and quality, avoiding any sudden deterioration by wind or rain and allowing a ready separation into their constituent parts. After harvest, stigmas must be separated from the tepals and stamen as soon as possible by opening the corolla and cutting the stigmas with the fingers below the branching where the style changes color (from red to yellow).
Tentative mechanization procedures of some crop techniques in saffron have been carried out, but it is a rather difficult crop. Lack of mechanization in saffron is certainly due to the delicacy of bulbs and flowers, which require handling with care, but also to the considerable variation in size of bulbs. Other reasons are the cultivation of saffron in countries with very low manual labor costs and, on the contrary, the limited areas of land to which this crop is devoted in high labor cost countries. Planting requires regular and correctly oriented placement of the bulbs. A modified onion planter has been used to plant saffron, but the impossibility of placing the bulbs with the apex in the upward direction led to a delay in emergence and a decrease in production. In fact, the bulb reduces emergence when the apex is not pointing upward. A potato planter was also tested, enabling more control for bulb orientation, but resulting in lower production compared with the onion planter. A normal hoeing machine can be used to mechanize weed control, by adapting row distance, especially in the first year. Lower efficacy was obtained the following year with the increase in weeds and the rising of the daughter bulbs. During the rest period of the crop, flaming was also used with good results against young weeds. If hysteranthy is manifested in saffron, flower harvesting can easily be mechanized with calibrated and adapted mowing or grass cutting machines, without cutting the leaves. No suitable results have been obtained for flower separation, while adapted bulb- and tuber-picking (such as a potato digger) can replace human labor successfully for corn lifting.
Drying and storage of stigmas
Drying and storage methods are very important because a poor undertaking of this procedure can completely compromise qualitative features of saffron. According to the ISO norm, the moisture content may range between 10 and 12% (ISO-3632, 2003). Many methods are used for the dehydration of saffron. Concerning Italian production, the stigmas are normally spread over a large area and dried at room temperature in the sunlight or with forced air. In Navelli, dehydration is traditionally carried out by placing the stigmas on a sieve 20 cm above a charcoal fire, while in Sardinia it is performed by drying stigmas in the sun or at room temperature (for several days) or in the oven at low temperature (35–40 ◦C) in less time until moisture is reduced to 5–15%. Saffron is sun-dried in India and Iran, and toasted over hot ashes in Spain, while it is dried slowly at 30– 35 ◦C in dark rooms in Greece; therefore, many procedures are applied and, as is usual in such cases, there are still substantial disagreements over the best drying conditions.
Storage of saffron must be done in the dark and possibly in a modified atmosphere, since saffron pigments are light-, oxygen- and temperature-sensitive. The best way to store saffron spice is to keep it hermetically closed in darkened glass containers, and possibly at low temperature (5–10 ◦C).
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Yield is quite a difficult parameter to forecast in saffron: saffron yield is in fact a function of many agronomic, biological and environmental factors able to exert a great influence on production. As far as is known, production is strictly influenced by dimension and storage conditions of bulbs, climatic conditions, sowing, cultural techniques (annual or perennial), crop management (irrigation, fertilization and weed control) and disease. Moreover, saffron production increases from the first to the third – fourth years of cultivation. Generally, one hectare of saffron may produce 10–15 kg of dried stigmas, but it can range widely, depending on the abovementioned factors, from 2 to 30 kg.
Yields of 2.5 kg/ha are reported in Kashmir, India and Morocco in rain-fed conditions, while it can reach 15 kg/ha in Spain under irrigation and fertilization. In irrigated Moroccan areas, yields of about 2.5–6 kg are obtained. In Iran, the average yield of saffron is around 5.4 kg/ha. In New Zealand, researchers reached yields of 24 kg/ha of dried stigmas. A production of 29 kg/ha was recorded in Navelli, but this is not comparable with the other yields because an annual cropping system is used and only the biggest bulbs are replanted every year.
Pests and Disease
The worst enemies of saffron are rodents and fungi. Moles, rats and rabbits can easily damage bulbs or eat leaves. Fungal attacks are mostly promoted by humid conditions. High moisture percentage together with high temperatures create ideal conditions for the rapid development and spread of nematodes and fungi (Fusarium, Penicillium, Rhizoctonia, etc.) and consequently bulb rot. These conditions generally occur in the hot and rainy spring. A study indicates that temperatures above 10–12 ◦C with rainy weather are a favorable climatic combination for the establishment of fungal disease on saffron. On the contrary, the hot and dry Mediterranean summer inhibits the spread of parasites. To avoid fungal infection, the best practices are crop rotation, the removal and burning of infected plants and bulb treatments with anti-fungal products before planting, such as benomyl or copper-based solution.
Saffron Express team hereby wants to cordially thank F. Gresta, G.M. Lombardo, L. Siracusa, and G. Ruberto for their inevitable endeavoring for the article of “Saffron, an alternative crop for sustainable agricultural systems”, which inspired us a lot during preparing this article.
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