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1/ Change the varietal range

When establishing an asparagus plantation, it is necessary to reflect on the choice of varieties, as well as on the setting of the asparagus and its management, with particular attention to irrigation. The varieties are characterised by their different cold needs during their vegetative rest period. Colder areas or temperate climates, such as northern European countries (e.g. Germany, the Netherlands, France) and those in North America (US, Canada) require 1,000 hours of cold (under 7oC), while intermediate areas, i.e. with a Mediterranean climate (e.g. Spain, Italy, Middle East, California, Mexico, Australia) need between 500 and 600 hours, and hot zones or warm areas (e.g. Peru, Philippines) have no need for cold at all. It is likely that global warming in temperate zones will alter the current varietal range in Northern Europe and North America. The varieties chosen will be less demanding of cold in order to facilitate their annual storage and ensure an economically satisfactory lifespan. For green varieties in particular, an increasingly important criteria will be tip closure rather than flowering under the effects of heat. Improving the quality of the spear is currently a major goal for all breeders.

2/ High ridges to limit excess water

Even if average temperatures are likely to increase, the overall rainfall of some areas, especially in temperate climates, should remain stable. However, the precipitation regime could alter, with very heavy rainfall accumulations in autumn and winter. This consideration is driving interest in planting on ridges (see box).

Ridge cropping is used to address water accumulation caused by very heavy rainfall, which could become increasingly more frequent. With this technique, planting is conducted at between 25 and 30 cm above ground level. Ridge cropping also allows natural drainage. Asparagus crowns are always found outside of the wet zone during wet and rainy winters or springs (see Asparagus World n°2/2020). A higher bed also results in more exposure, which leads to faster drying. Localised irrigation is a must in order to concentrate moisture at the foot of the plants. With this method, about 10% more input will be required on the row and per hectare. Another consideration is planting depth. Reducing depth also lowers the risks associated with excess moisture (asphyxiation, root diseases, etc.). Precocity can improve with faster soil warming: 1 cm less in planting depth = 1 day more precocity.

3/ Optimise Irrigation

Irrigation provides new roots with moisture at the plateau level during harvest; this is mainly for green asparagus, but also for white. Each new spear produces 1 to 3 roots at its base. Close monitoring of root development is required to ensure constant humidity and allow the right humidity at depth. If these new roots are in drought, this will result in a lack of calibre, wrinkled spears, and loss of tip quality; in very harsh drought conditions, the spear can become completely dehydrated. On the other hand, supplying water ensures better calibres and yields and less flowering of the tip.

4/ Culture Management

Sprinkling and shading can limit flowering and improve the quality of green asparagus. The spear contains more than 90% water and it is difficult to protect the skin from the aggression of the sun and wind and from too low hygrometry levels. In the greenhouse, two or three rounds of sprinkling during the hot hours maintains a humidity of above 80%, which is required to harvest a spear that is turgescent, un-wrinkled and of good calibre. Supplementing the moisture supply with sprinkling also lowers the ambient temperature.

Tall grass between the ridges creates a micro-climate, which reduces the risk of frosts and regulates the temperature by +1.5 degrees. The planting of long grass also reduces the effects of wind and prevents mulch from being blown away during storms.

5/ Night harvesting

Harvesting at night protects asparagus from the daytime effects of the sun and dehydration. Asparagus harvested at night is colder, whiter and less fibrous. Professionals practising this technique find that spears harvested at night are 10oC cooler than those harvested in the middle of the day. The cooling and storage process is facilitated during calibration and packaging. Asparagus harvested at night is also of better quality: it is straight, less fibrous, and has better calibre. Night harvesting often takes place in calm weather to avoid possible damage caused by the often dry wind to green asparagus, which bends. Indeed, wind affects the skin on the exposed side of the asparagus, and this invisible wound results in curvature.

6/ Put the asparagus under cover

Like many other crops that suffer from increasingly frequent climatic “accidents” (hail, high winds, intense rainfall, etc.), planting asparagus in greenhouses is an increasingly feasible practice. At the beginning of cultivation, greenhouses can regulate climatic jolts and bring more precocity, which often equates to better selling prices. The gain depends on the structure (greenhouse, plastic) and the volume of the greenhouse (tunnel, multi-span).

Mini-tunnels (Engels type) provide three weeks of precocity compared to the open field and 20 to 30% more yield per hectare.

Plastic tunnels, 5 to 9 m wide, provide 4 to 5 weeks of precocity and 30 to 50% more yield.

Multi-span tunnels provide a gain of 5 to 7 weeks of precocity with 40 to 70% more yield per hectare.

Yields are improved by the favourable conditions when growing in spring, but also by the longer vegetative period in the spring and autumn which increases the accumulation of reserves in the crown. Greenhouses also improve working conditions, making the harvest more comfortable and efficient thanks to the regularity and density of the spears to be harvested.

Today’s new horticultural greenhouses equipped with photovoltaic panels mean that we can enjoy the benefits of sheltered production with a limited financial outlay. Investments in greenhouse structure are supported by energy-producing partners. However, in this type of greenhouse, the percentage of shade can be very important and become a limiting factor in terms of the precocity, productivity and longevity of the crop. Hence, the design of the sheltering structure is also crucial to its success.

Read Also: The major challenges of climate change  

Asparagus for processing, canning and freezing is subject to different production constraints from asparagus for the fresh market. Two parameters are decisive for this type of culture. The availability of deep, sandy land with good water resources is a primary agronomic parameter. The availability of labour at the lowest possible cost is a second determining economic criterion. The history of asparagus production is marked by the industry’s migrations driven by changing labour costs and availability, while at the same time maintaining the same distribution markets in North America and Europe. Canned or frozen asparagus left France in the mid-1980s, when Spain entered the Common Market and was able to offer lower labour costs and receive subsidies.

 

Motivated by low labour costs

In 1995, the Spanish asparagus industrialists set up in Peru attracted by the availability, cost and efficiency of Peruvian workers. This explains why there is no longer an asparagus canning industry in Europe with the exception of the PGI Asparagus of Navarra. Faced with the rising costs and scarcity of Peruvian labour in around 2005, some of the companies decided to set up in China. But China’s economic and industrial boom over the past decade has seen a steady flow of workers leaving the countryside to be absorbed by the construction and industrial sectors. Now, new asparagus manufacturers or the same companies that were in Spain, Peru and China are setting up in Africa. These players have mainly chosen Namibia, Ethiopia and Madagascar for various reasons. Each of these African countries already has between 100 and 400 hectares in place in less than 5 years with a projected 400 to 600 hectares more in the future. The primary driving force for these new implantations is the low labour costs available. Thus, the average daily cost including expenses is estimated at US$3 per worker in Madagascar and Ethiopia and $5 in Namibia, compared with $10 in China, $20 in Peru and $60 in Spain. The availability of a large number of workers is also critical to the decision.

 

Need for mulch in asparagus production

Another asset the African continent has is access to good, deep, virgin land at reasonable prices. Prices are about $5,000 to $10,000/ha. However, these are fallow lands that require a lot of work to grow crops. While Peru enjoys very stable temperatures throughout the year (between 12 and 30 degrees) these African countries, in contrast, have much greater climatic ranges, going from 5 to 30 degrees Celsius in Madagascar, up to 35 degrees Celsius in Namibia, and up to 40 degrees Celsius in Ethiopia. The winter period does not allow production, and summer temperatures are too high (especially in Ethiopia and Namibia), slowing or stopping production. It is therefore obligatory to use mulch for warming and to ensure the production of asparagus in the spring and autumn. Even if asparagus crops are at altitude (between 1,000 and 2,000 m) in order to escape the excessively high summer temperatures, the soil must be refreshed with irrigation water. Water is available in sufficient quantity and quality from dams or deep boreholes. On the other hand, the rains are irregular and difficult for the local meteorological services to predict.  For Madagascar and Namibia, located in the Southern Hemisphere, the period of precipitation is between November and March. For Ethiopia, in the Northern Hemisphere, it rains the most between June and September. These rains can interrupt water stress and complicate harvesting and health protection. Without special measures, these new zones can only produce 3 to 5 months a year, which impacts heavily on the returns on the very high investment costs for asparagus fields.

 

Essential technical adaptations

With the benefits, however, come certain constraints and difficulties. Indeed, while the workforce is often plentiful, skill and motivation levels may be low or entirely absent. For many workers, asparagus is a totally unknown crop, which requires time for training and learning. Careful management is crucial if the expected economic gains are to be achieved. Even if local, this workforce is often very scattered, with no means of transport. The company must therefore implement transport logistics to move its workers and sometimes even house them, which in turn requires constructing housing. Untouched asparagus-friendly land may also be land which has been poorly cultivated previously. The parcels sometimes require levelling work as well as the construction of basic infrastructure (roads, wells, etc.) to make production possible. These “new Eldorados” also require technical adaptations and new expertise in cultivation to adapt to climatic conditions that are different from areas already cultivated in the world. In

some cases, climate data is deficient or non-existent. These new destinations for asparagus have no nearby bases for the supply of inputs. It is therefore necessary to import all means of production, storage and packaging, which involves time delays that sometimes require order growing equipment 7 to 10 months in advance. The resulting costs can very quickly reduce or even wipe out the expected economic gains. In addition to the very high cost of air cargo, between $1.5 and $2/kg, it is also important to take into account the remoteness of international airports, the average regularity of domestic flights, the few tarmac roads, and the numerous tracks; remoteness of ports for sea freight (1 to 2 day’s transport). Also, it is almost impossible to export fresh asparagus. In order to get the best value from the product, it must be transformed either by appertisation (canning) or, more riskily, by freezing. Both cases require very costly agro-industrial equipment.

 

Danper

Three markets for Peruvian asparagus

Peru-based Danper has been processing white asparagus for canning since 1994. In its early days, the company sourced from the producers of its own region. It was not until 2002, after acquiring some land, that it began producing and marketing white asparagus for fresh export markets. “Fresh white asparagus has to be of a high quality level and there must be total control of the production chain until shipping,” said Danper’s director Jorge Aranguri. Then, in 2004, the company invested in its own freezing unit, mainly to freeze green asparagus. Today Danper has over 1,100 hectares of its own asparagus, with an additional 1,000 hectares belonging to various partner producers. The average yield of asparagus is around 10 tons/ha. Asparagus production takes place all year round, which means three markets can be supplied: fresh, canned, and frozen, according to the different qualities of asparagus and market prices. “Our peak production of white asparagus for the fresh market runs from August to December,” said Aranguri. For this market, calibres above 14 mm are preferred. For canning, calibres of 9 to 12 mm after peeling are desirable. “We have different opportunities due to the different quality requirements. This allows us to make the best use of all types of asparagus and to adjust to the markets,” said Aranguri.

 

 

 

 

After harvest, white asparagus undergoes physiological and biochemical changes that rapidly lead to a loss of quality. The main effects are higher fibrosity, water loss, and the development of a pink discolouration due to an increased synthesis of anthocyanins. The pink discolouration is a criterion that depreciates product quality and, depending on the distribution channel, may entail downgrading to a lower class, with a possible price loss of 5 to 15% for the grower, according to a survey by CTIFL (2017).

Spears immersed in hot water show practically no pink discolouration

Several studies have shown the advantage of rapidly lowering the temperature of asparagus with cold (6-8°C) or iced water by spraying or immersion (hydrocooling) in order to delay the appearance of this pink tint. In an article published in Infos Ctifl nr. 353 (July 2019), Patricia Sanvicente, Sophie Annibal and Valérie Mérendet write that « rapid cooling after harvest is currently the most widely used technique in France ». Based on literature (see boxed text), new studies were conducted by CTIFL in 2017 and 2018 in order to assess the interest of hot water treatments applied to white asparagus varieties. Thus, in 2017, the hot water treatment of the varieties Darlise (little susceptible to pink discolouration) and Vitalim (highly susceptible) was applied by immersion of the spears, followed or not by a hydrocooling treatment using spraying. The core temperature of the spears during the trials was maximum 47-50°C for immersion treatments at 55 °C. The spears returned to their initial temperature after 30 minutes at room temperature (18 °C) or were cooled to the core at 3° C in less than an hour if the hot water treatment was followed by hydrocooling (2 °C/20 min). In the trials, the spears immersed in hot water showed practically no pink discolouration, whereas the control spears, hydrocooled and immersed in water at room temperature, took on a pink tint after 5 to 6 hours in simulated point-of-sale conditions, with the discolouration further evolving over the three days of exposure to light (Figure 1). As the authors observe, « pink discolouration of white asparagus is strongly delayed by immersion in water at 55 °C ».

Towards a large-scale implementation?

In the experiments, techniques combining a hot water treatment applied by dipping or spraying within 3 or 4 hours after harvest, followed by hydrocooling or immersion in temperate water (Mérendet & Annibal 2015) offer the best compromise in order to limit pink discolouration and water loss. Using this method, the core temperature of asparagus decreases rapidly and the spears are quickly cooled down before storage. As the authors of the article state, « Before those techniques can be applied on a large scale, the growers will have to confirm the feasibility of introducing the various steps into the organisation of the packing stations, as well as the positioning of the existing equipment. ». If one of the two proposed methods is deemed to offer perspectives for implementation, the advantage of a hot water treatment will have to be validated at the grower’s facility using existing or specifically adapted equipment.

 

Why does white asparagus turn pink?

Anthocyanins are pigments that filter light; they accumulate in plant tissue in response to the action, joint or separate, of various environmental factors, such as light (Leyva 1995), low temperatures (Christie et al. 1994, Dixon 1995) or nutritional stress, e.g. a phosphorus deficiency (Kakegawa et al., 1995). As a reaction to those factors, the activity of phenylalanine ammonia-lyase (PAL), a key enzyme in the pathway of anthocyanin biosynthesis, is stimulated (Dixon 1995, Flores et al, 2005). In the case of white asparagus, research indicates that there is an increase in the activity of PAL, and therefore enhanced postharvest anthocyanin synthesis, after an initial stimulation by light, independently of temperature and lighting conditions during storage, thus causing the appearance of a pink tint (Siomos et al. 1994, Siomos et al. 1995a, Siomos et al. 1995b; Siomos et al. 2000; Siomos et al. 2001, Flores et al. 2005).

 

Existing data

Research in the Netherlands showed that a hot water treatment (50 °C/2 min) limits the appearance of a pink tint in white asparagus (Poll 1998). More recently, Siomos and his team (2005, 2010) confirmed that, in experimental conditions, heat treatment by immersion in hot water is efficient in preserving the white colour of asparagus spears. A treatment by immersion in hot water at 55 °C for 2 to 3 minutes, followed by an immersion in water at room temperature for 10 minutes, is efficient against pink discolouration in the varieties Atlas and Dariana. Similar results were obtained in preliminary research conducted by CTIFL in 2015 on the variety Grolim (Mérendet & Annibal 2015).

 

Spraying or immersion?

In 2018, hot water spraying was tested by CTIFL in order to determine if this method was as efficient as immersion in limiting the appearance of a pink tint in asparagus. The technique was assessed using several combinations of temperature/duration, systematically followed by hydrocooling through immersion (1 °C/5 min). In the spraying treatment, asparagus spears in plastic crates were placed under two spraying nozzles supplied with water heated and regulated at the desired temperature. As in the « immersion » trials, the spears in the « control » batch and the « hydrocooled » spears took on a faint pink hue within a few hours of their transfer into point-of-sale conditions. After 24 hours in said conditions, 90 to 100 % of the spears showed a fairly marked pink discolouration (colour index 70 to 80). However, spraying with hot water 3 to 4 hours after harvest, followed by hydrocooling through immersion, limited the appearance of a pink tint. The best results for each tested treatment temperature were obtained with the longest exposure. On the other hand, a heat treatment 24 hours after harvest was less efficient than a treatment within 3 or 4 hours after harvest. In the experimental conditions, the temperature/duration combination of 58 °C/90 sec was the most efficient to avoid pink discolouration of the spears. Unlike the results of the « immersion » trials, which showed a very slight dehydration of the spears (0,1 to 0,2 %), the heat treatments using spraying did not entail any weight loss. On the contrary, the spears gained an average of 2 % of their initial mass by absorbing water during the treatment.

 

There are several reasons for harvesting asparagus at night. One of the main ones is that it assists pickers – a key consideration given that Spain has very few machines to assist in harvesting. Our Andalusian labourers find that the plastic is soft in daytime temperatures and doesn’t handle well. Also, as asparagus harvesting is a laborious task, the workers feel less fatigue at night, which allows them to work at a better pace. For night vision purposes, they use headlamps. However, handling asparagus is a delicate endeavour that requires care and precision to ensure the quality and integrity of the product is maintained throughout the production process. This is why we always employ expert and reliable pickers. The harvesting usually starts at 10 pm and ends between 4 and 7 in the morning, depending on the amount of asparagus.

Another benefit of harvesting asparagus at night concerns the quality of the product. Picking the plant at this time allows the asparagus to come out cooler and whiter as it avoids contact with sunlight. This in turn ensures a better appearance and taste – key considerations for retailers and consumers alike. The third major factor relates to operational organisation. When all of day’s production is carried out early in the morning, you can start organising the storage house very early and begin processing the production for sale and delivery. This ensures the product arrives on the market as fresh as possible. So, we feel there are more advantages than disadvantages relating to night collection. We should never forget, however, that the pickers’ expertise and skills are at the heart of the process.

The night harvest would seem to be a complex operation. Yet the producers who have tried out the experiment in different countries have all done so successfully. Today, it represents a trend that is spreading in several parts of the world.

Natural temperature lowering

The goal of the night harvest is to optimise conditions for the preservation of asparagus during and after collection. It avoids the light (colouring of the tips), heat, low humidity, and wind that often lead to the rapid dehydration of asparagus. Depending on how the work site is set up, the process starts either at the end of the day or in the middle of the night. In both cases, the aim is to have the bulk of the harvest completed by between 6 and 8 am in order to start washing and packing early, and, above all, so as to know the precise quantity and quality of the asparagus to be marketed. The night harvest takes advantage of the natural lowering of the temperature. Asparagus harvested in this way can be 3 to 8 degrees cooler than asparagus harvested during the day. This makes cooling easier and improves the preservation and quality of the product. The night harvest hinders the bud growth that appears under plastic after the day’s temperature peak. As a result, the percentage of burnt spears is lower. Asparagus harvested at night is whiter. Its development in the mound happens during the day, and the tip appears later. Once harvested, the spears are no longer exposed to light.

Knowing the volume allows better marketing

Nocturnal conditions also provide higher relative humidity, which limits dehydration that can result in pinking. Moreover, there is little or no wind interference when handling the plastic covers. As the reports show, most teams of pickers enjoy working in cooler and less demanding conditions. The night harvest also optimises the management of packaging, which is particularly important as once sorting teams start work, they have to handle large volumes. The station manager can also adapt the number of operators to the volume of the night’s harvest as the available volumes are known very early in the day. This improved knowledge of the offer makes it possible to make the most of the daily harvest.

5 benefits of the night harvest

– colder asparagus: between 3 and 8 degrees less than during the day harvest

– better quality, resulting especially from fewer burnt tips

– no pinkness due to darkness, higher relative humidity and often less wind

– knowledge of harvest volume facilitates organisation of sorting work

– better knowledge of the offer and better daily valuation

Night picking revolutionises harvest in Alsace

As soon as they get out of the van, the small group disperses into the plot. It could be 7:00 in the morning, but it’s actually 7.00 in the evening. This is the usual time when the working “day” begins. Emmanuel Dollinger, manager of Dollinger Farm, welcomes his first group of eight Spanish seasonal workers for the 2018 season. The farm has completely overturned its harvesting routine, which used to start at 6 am and end at noon, or sometimes later. “Last year it was very hot. After ten days, Juan, the team leader suggested starting work at 7 pm or 7:30 pm, telling me that at night, you don’t suffer from the heat, and that you are more efficient and quieter,” recalls Dollinger. At first, the farm manager was reluctant but was eventually persuaded to give it a try using headlamps. The test results provided such positive results that within a fortnight, the group had become familiar with the single 10-hectare plot. Today, Dollinger is completely free to manage his time and harvest according to the weather, “as long as I have the maximum amount of asparagus waiting for me in the morning in 6 kg crates. Juan knows his stuff. He is 47 years old and has twenty-eight years of experience in asparagus.” For Dollinger, the 2018 campaign represented a revolution in crop management. “I’m a winner in every way,” he said. “When I start my day at 7:00 am, all I have to do is count the crates to instantly know how much volume I have for sale.” Sales have increased and some customers have pointed out that the quality of asparagus has improved.