Archive

Die ca. 20 ha Spargelanbau auf schweren Böden mit einer Kiesschicht und einem durchschnittlichen Jahresniederschlag von 810 mm stellten ihn dabei vor große Herausforderungen. Bereits seit 2015 unterliegt die Wahl aller Bewirtschaftungsmaßnahmen im Betrieb dem vorrangigen Ziel, Bodenverdichtungen zu verhindern.

Seit 2019 bemüht man sich darüber hinaus die 5 Prinzipien der Regenerativen Landwirtschaft für den Spargelanbau anzupassen:

1 Dauerhafte Bodenbedeckung

2 Dauerhaftes Vorhandensein von lebenden Wurzeln

3 Förderung der Biodiversität in und über dem Boden

4 Minimale Bodenstörung durch reduzierte Bodenbearbeitung

5 Integrierung von Tierhaltung

Die grundsätzliche Zielsetzung der Regenerativen Landwirtschaft ist es, durch Wiederherstellung der natürlichen Prozesse, das gesamte Ökosystem zu stärken und zu regenerieren. Die zentrale Funktion übernimmt hierbei der Boden als komplexes Ökosystem, da er eine wesentliche Rolle hinsichtlich der Biodiversität, der Pflanzengesundheit und durch die Speicherung von CO² auch für das Klima spielt. Ein gesunder Boden speichert mehr Wasser, ist widerstandsfähiger gegen Überschwemmungen und Dürre, liefert mehr Nährstoffe für die Pflanzen und belastet das Grundwasser nicht. Die Umsetzung dieser Ideen findet beim Spargelanbau im Rafzer Feld vor allem durch die Einsaat von zwei Gassenbegrünungen im Laufe des Kulturablaufes, sowie durch die Düngung mit einer selbst entwickelten Terrapreta statt. Diese Komposterde setzt sich zusammen aus festem Gärgut, Pferdemist, Pflanzenkohle, Gesteinsmehl, Melasse und EM (Effektive Mikroorganismen) und reift in Form einer Feldrandkompostierung 4 Monate lang unter einer Abdeckung von Grünschnitt.

Nach der Fertigstellung und Abdeckung der Dämme

Nach der Stechperiode werden die Spargeldämme mit einer Scheibeneggenkombi komplett abgetragen. Dies ist notwendig, um den organischen Dünger mit dem Kompoststreuer gleichmäßig auszubringen. Danach findet eine Tiefenlockerung der Gasse bei gleichzeitigem Einspritzen von EM (200 l/ha) statt. Direkt im Anschluss wird auf den Spargelflächen im Rafzer Feld mit Saatkasten auf Kreiselegge und Walze eine abfrierende Begrünungsmischung in den Gassen ausgesät (s. Foto 1). Das Mulchen von Begrünung und Spargelkraut findet für die zu verfrühenden Anlagen im Oktober in zwei aufeinanderfolgenden Arbeitsschritten statt. Nach der Fertigstellung und Abdeckung der Dämme erfolgt dann die zweite Begrünungsaussaat mit Winterweizen mit einer Säkombination beidseitig des Dammes. Diese Begrünung bleibt dann bis zum Ende der Stechperiode stehen und wird erst mit dem Abdämmen umgebrochen.

Verschlämmungen und Verdichtungen stark vermindert werden konnten

Die in der Regenerativen Landwirtschaft angestrebte andauernde Bodenbedeckung durch Begrünungspflanzen ist im Spargelanbau durch das Auf- und Abdämmen kaum umsetzbar. Doch die Praxis der zweifachen Begrünung der Gassen stellt eine Annäherung an die Zielsetzung dar und führt zu  einer nachhaltigen Verbesserung des Humusgehaltes im Oberboden. Durch Verwendung des Schmalspurschleppers für die Aussaat der Begrünung wird die tiefgelockerte Gasse nicht befahren. Die Walze nach der Einsaat der Begrünung schließt den Oberboden, wodurch aerobe Prozesse die zur  Nitrifikation führen direkt unterbrochen werden.

Bereits im zweiten Jahr ließ sich erkennen, dass sich durch die Umsetzung der beschriebenen Maßnahmen die Befahrbarkeit während des Stechens mit den Spargelspinnen verbessern liess, dass die Wasseraufnahme nach Starkregenereignissen erhöht war und Verschlämmungen und Verdichtungen stark vermindert werden konnten.

There’s year-round demand for fresh green asparagus in the UK, however, the UK asparagus season is short and averages just 5,300 tons. What’s more, the local spears suffer from a relatively short shelf-life resulting in substantial waste at times of peak production, when it is difficult to manage asparagus yield and consumer demand. To meet the shortfall in supply, nearly 12,000 tons were imported by the UK in 2022, much coming by air freight from Peru and Mexico. Being able to prolong storage-life while maintaining the quality of UK-grown spears would have benefits including reducing food loss and the carbon footprint of imports. Currently, maintaining asparagus quality using cold storage alone is limited to one week, after which the spears have about a seven-day shelf-life in retail outlets. One of the factors limiting a longer life in cold storage is the onset of the postharvest physiological disorder tip breakdown. Also (erroneously) known as tip rot, this disorder occurs only sporadically during the shelf-life of chilled or cold stored spears; and often the first symptom is an unpleasant aroma. Unfortunately, this ‘off’ smell usually ends up causing the whole batch of asparagus to be discarded even if only some spears are affected by tip breakdown. While microbes appear to be off the hook, the underlying causes of tip breakdown remain to be discovered.

What is already known about tip breakdown

Initial investigation into tip breakdown suggests its origin is physiological ⁽¹⁾, not pathological, developing in the rapidly dividing cells of the spear tip ⁽²⁾ during periods of hot weather. (High levels of tip breakdown across the UK in 2018 coincided with an unseasonably warm harvest season.) Fast growth and reduced levels of non-structural carbohydrates have also been linked to a higher incidence of tip breakdown ⁽³⁾, and it has been noted that warm adapted asparagus genotypes, such as ‘Jaleo’, have lower susceptibility than cold adapted ones, such as ‘Gijnlim’. Nevertheless, despite previous research, the underlying causes of tip breakdown have not yet been fully elucidated. Since 2020, researchers* in the UK have thus been on the hunt for the true culprits causing this disorder. Hailing from Cranfield University (Plant Science Laboratory and Environmental Analytical Facility) and Cardiff University (School of Biosciences), they are being led on this project by JGHC Ltd, which is linked to Cobrey Farms, where 40% of the UK’s asparagus is grown. Once the factors responsible for tip breakdown are identified, they hope to develop a decision support tool to identify pre-symptomatic tip breakdown spears.

‘Early California’ and ‘Aspalim’ spears under the microscope

Does fast growth or a slow rate of sugar transport play a key role in tip breakdown? To test these theories, the researchers chose two asparagus cultivars with low and high susceptibility to tip breakdown, the warm acclimated ‘Early California’ and cold acclimated ‘Aspalim’, respectively, and grew them under a cold controlled temperature regime (18/8°C, day/night) as well as a warm one (28/14°C). Harvested spears were cut to a length of 16 cm, packaged into shelf-life trays, wrapped in commercial film and stored at 7°C to assess the development of tip breakdown. Sampling took place on days 14 and 21. The top 4 cm of each spear sampled was snap frozen and underwent biochemical analysis of non-structural carbohydrates and plant growth regulators (PGRs), followed by statistical assessment.

More susceptible: spears that grow fast under hot conditions

‘Early California’ seemed to grow at a slower rate than ‘Aspalim’, though the growth rate for both was significantly lower under the cold compared to the warm conditions. What’s more, tip breakdown was not observed in any of the spears grown under cold conditions. Under the warm regime, however, the problem appeared in both and although overall the incidence was not that high, it was twice as much for ‘Aspalim’ than for ‘Early California’. Such results are in line with work by other researchers ⁽⁴⁾ who found that tip breakdown occurred under warm growing conditions.

Spears with tip breakdown had less sugar

As for sugar content, the UK researchers found that fructose concentrations were lower in spears with tip breakdown than in healthy spears. Further experiments will be needed to see whether the decreasing trend in sugar content towards the end of the harvest increases predisposition to tip breakdown, they said. Also of note is that the ‘Aspalim’ spears grown under cold conditions had an overall higher sugar content (fructose and glucose) at harvest than the warm-grown spears. These results are in line with previous studies where asparagus grown in the field under cooler, more favourable growing conditions resulted in spears with higher sugar content and better quality during storage ⁽⁵⁾, they said.

Tip breakdown and postharvest senescence are likely to be different processes

In prior studies ⁽⁶⁾, higher levels of the plant growth regulator abscisic acid (ABA) in asparagus tips was associated with lower quality spears. However, in the current research, after 14 days of cold storage, it was healthy spears, not those with tip breakdown, that had significantly higher concentrations of ABA. The researchers said it could therefore be hypothesised that tip breakdown disorder and postharvest senescence in asparagus are two independent processes which may be governed by different molecular pathways. A more detailed hormonal study, quantifying cytokinins and auxins, plus a transcriptomic analysis, would aid in fully explaining what role, if any, that plant growth regulators have in the incidence and development of postharvest tip breakdown in asparagus spears, they said.

Studying tip breakdown at molecular and cellular level

Does spear cell size have something to do with tip breakdown? Or could changes in gene expression have a key role? To explore these hypotheses, the researchers studied the cellular mechanisms of tip breakdown. Once more, ‘Aspalim’ and ‘Early California’ cultivars were chosen and were grown under cooler and warmer controlled conditions as described above. Harvested spears were stored at 7^oC in the dark for 14 days and tip breakdown was assessed visually.

Cellular analysis appears to rule out cell size as a culprit

Among the reasons to suspect a role for cell size in tip breakdown is the link to faster spear growth. This led to the hypothesis that this may result in larger, weaker cells that are more susceptible to postharvest tip breakdown. However, an examination of cell sizes for ‘Aspalim’ (susceptible to tip breakdown) and ‘Early California’ (a variety in which it very rarely occurs) – at both higher and lower growth temperatures – did not reveal any significant differences in cell size.

RNA analysis a potent tool for studying gene expression, metabolic activity

RNA sequencing (RNAseq) was used to investigate any changes in the genes being switched on and off in asparagus spears affected by tip breakdown. Also known as transcriptome sequencing, RNAseq is a powerful method for revealing changes in metabolic pathways that may be involved in the development of postharvest disorders. The publication of the asparagus genome has greatly facilitated this approach.

On analysing spears after 14 days of shelf-life, many genes were found to be upregulated in those showing tip breakdown compared to healthy spears that had been grown and stored under the same conditions. The authors said that this was “perhaps surprising” and suggests the process of tip breakdown is an active, not passive one. This might indicate that tip breakdown is not due to necrotic cell death (such as excessive heat might cause), although further work is needed to confirm this. Preliminary analysis of the types of genes that change in expression during tip breakdown revealed a high proportion of genes involved in reprogramming activities in the cell and may therefore be involved in regulating the progression of tip breakdown. Several metabolism-related genes were also altered in expression, including transferases, oxidoreductases and O-methyltransferases. “Understanding the role of these genes may help us identify the mechanisms controlling the tip breakdown. This could lead to the discovery of pre- or postharvest treatments or provide breeding targets to improve resilience to tip breakdown in more susceptible asparagus varieties,” the researchers said.

*Principal Investigators: John Chinn (JGHC Ltd – overall lead), Dr MariCarmem Alamar (Cranfield University), Prof Hilary Rogers (Cardiff University)

Find out more:

https://www.cranfield.ac.uk/people/dr-m-carmen-alamar-498015

https://www.cardiff.ac.uk/people/view/81265-rogers-hilary

https://www.cranfield.ac.uk/research-projects/asparagus-tip

Asparagus was first introduced to Japan by the Dutch during the Edo Period (1603-1868), but as with many exotic plants, it was initially grown as an ornamental rather than for eating. In the early 20^th century, cultivation of white asparagus began in Hokkaido, mainly for export to the European market, although it was also served at a select few high-end French restaurants in Japan. It was not until the early 1970s that asparagus was widely cultivated for domestic consumption, with the green type dominating. Satoru Motoki of Meiji University treated attendees at the IAS 2022 conference in Cordoba (Spain) last June to an engaging talk about the Japanese asparagus sector and provided insights into the many research projects underway “to achieve high quality at each stage of asparagus production, marketing and consumption”. Asparagus has become one of the most popular vegetables in Japan and is widely cultivated across various regions of the country with green, white, purple and pink spears. While green asparagus remains the most popular among Japanese consumers, a recent trend towards diversification in dietary style has emerged, leading to an increase in the popularity of white asparagus. This trend has also driven a rise in cultivation area dedicated to purple and pink asparagus. The marketing of asparagus in Japan has become diverse in recent years, with consumers seeking uniqueness and variety. This has resulted in the marketing of different forms and sizes and the introduction of new kinds of asparagus, such as mini-asparagus, and three-colour sets of asparagus.

Rise of pink asparagus

The Japanese employ the different coloured asparagus in a variety of ways. Green asparagus is the most popular for eating in its fresh raw form. Besides being marketed in different colours, the asparagus spears also come in various lengths and shapes. As Western cuisine has become increasingly popular in recent decades, Japanese people have been drawn to white asparagus as something new and tasty to try. Similarly, the cultivation of purple asparagus for eating in its fresh form has also begun to increase. And it’s not only taste that counts in Japan. Aesthetics also plays a key role in the country’s cooking, which is part of the appeal of innovative pink asparagus, which has been gaining attention in recent time as consumers attach importance to uniqueness. Pink asparagus is prepared by shielding purple asparagus from light to make white asparagus, and subsequently applying light to it until it takes on a pink colouration.

New techniques emerging

Meanwhile, domestic output has remained relatively unchanged for the past 26 years, averaging around 30,000 tons annually, ranking Japan 8^th at the global level. Asparagus is grown in different parts of Japan to harness the full potential of its various climates. Hokkaido Prefecture is Japan’s largest asparagus producing region, where around 3,300 tons is grown on average each year. The other growing regions are Saga Prefecture (2,900 tons), Kumamoto Prefecture (2,100 tons) and Nagano Prefecture (2,100 tons) (Japanese Ministry of Agriculture, 2022). The climate in these prefectures ranges from subarctic to subtropical, allowing for the production of asparagus in a variety of cropping types.

Hokkaido Prefecture has a climate similar to that prevailing in the northern part of the United States and Canada and in Northern Europe (Germany, the Netherlands, Poland, etc.), while Saga Prefecture and Kumamoto Prefecture have a climate resembling that along the western coast of the United States. Due to its high soil adaptability, asparagus is considered an excellent crop for growing in Japan’s upland fields that have been converted from paddy fields. To address the lack of off-season product, Japanese farmers have developed new techniques for year-round asparagus production. One technique that is spreading quickly is called fusekomi forcing culture, while another innovative method is the whole harvest cultivation method for one-year-old plants, which enables the cultivation of asparagus in larger quantities in a shorter period of time.

Fusekomi forcing culture

“Fusekomi forcing culture is a technique employed to be able to harvest asparagus during winter. Unique to Japan, production via this method is performed in part by using dug rootstocks,” said Motoki, and it plays a key role in the country’s asparagus production in the winter and early spring (December to March). The technique involves cultivating the asparagus rootstock for a short period of time (about 1-2 years) in an open field, digging it up in the autumn and planting it into beds arranged within a greenhouse, followed by warming until the spears are harvested. However, as Motoki pointed out, this approach “requires digging up the rootstock, which means that there is a need for specific farming machines and special skills. It is also necessary to have a special facility such as greenhouse in which the dug-up rootstock can be planted.”

Whole harvest cultivation method for one-year-old plants

A simpler technique developed by Motoki and colleagues is the whole harvest cultivation method for one-year-old plants. One benefit offered by this method is its brevity, with the cultivation process completed within one year of planting the seedlings. Conventional cultivation techniques require several years before a stable yield can be established. “Another advantage of this technique is that it involves lower risk of disease and pest damage. Cultivation from thfe same plants over many years results in increased likelihood of such afflictions occurring each year,” said Motoki. What’s more, the whole harvest cultivation method for one-year-old plants can even be employed by beginners without too much training necessary. Launched in 2016, and the first of its kind in the world, this technique is currently spreading rapidly across Japan thanks to the combined efforts of the government, Japanese agricultural cooperatives (Zen-Noh) and private enterprises. The method has been the focus of multiple TV programmes and newspaper and magazine articles that have attracted growing attention. In the academic realm, since 2020, researchers at Meiji University have been studying cultivars/lines selection using the whole harvest cultivation method for one-year-old plants in cooperation with Walker Brothers, Inc. of the United States.

Reusing plant parts

Researchers in Japan have also been exploring ways to make production more sustainable and resource-efficient by employing the parts of the asparagus plant that are normally discarded, such as its cladophylls. Despite Japan’s production of cladophylls totalling approximately 130,000 tons per year, only a small fraction gets utilised, with the rest either going to waste or returned to the field. Studies have shown that the beneficial component rutin is most abundant in the cladophylls and in the storage root of asparagus plants, while another valuable component, protodioscin, is most abundant in the buds and underground parts. Therefore, all of these parts offer great potential as rich sources of nutrition. Were storage roots to be left in the ground, besides making use of their valuable properties, another upside would be that it avoids the need to dig them up and saves labour. However, it has been found that if the storage root remains in the soil at the time of replanting, a growth inhibitor leaks out of it. “One way to supress this growth-inhibitory activity is with the use of active carbon,” said Motoki. So there is certainly great potential in utilising parts such as cladophylls and storage roots as it offers the potential to reduce waste, provide greater nutrition and save labour.

As long as the current levels of demand for asparagus hold in Japan, it is likely that new techniques will continue to be developed for growing this healthy and delicious vegetable and new varieties proposed to attract an even wider customer base.

1/ Pulverising destroys and removes the plant mass (foliage + weeds) accumulated during the autumn. Pulverising is either lateral (off-set) or frontal. Vegetation can be directed into the inter-row.

2/ Spreading the ridges (haulm extraction) allows the row to be cleaned for green asparagus or the mound for white asparagus. The burning of green asparagus haulm is also practiced.

3/ After the addition of organic matter on the row, the work of the new season begins with the bed-forming and installation of plastic mulch covers, then the installation of the hoops for the maintenance of mini-tunnels (early culture) and the filling of the pocket mulch (for wind resistance).

Carence en Magnésium

Symptômes

• Sur pousses âgées : cladodes de couleur jaune or, voire desséchées si la carence persiste. La tige reste verte.
• Sur jeunes pousses, les symptômes sont moins marqués.
• Particularité : le magnésium est très peu mobile dans la plante.

 Rôle du Magnésium

• Elément important pour la synthèse de la chlorophylle et la photosynthèse.
• Participe à la synthèse des éléments stockés dans les racines (sucres, protéines…).
• Fondamental pour la construction cellulaire, principalement en phase de croissance de l’asperge.

Pertes racinaires

• Réduction très importante du poids des racines : 60%.

Carence en Potassium

Symptômes

• Décoloration du bout des cladodes presque identique au magnésium, avec un dessèchement plus prononcé.
• Pousses âgées : jaunissement et dessèchement de la végétation si la carence persiste.
• Particularité : la potasse est très mobile dans la plante.

Rôle du potassium

• Régulateur des stomates et de la transpiration. 
• Améliore les réserves en sucre.
• Intervient sur la résistance au gel.

Pertes racinaires

• Réduction importante du poids des racines : 40%.

Carence en Soufre

Symptômes

• Entraine une moindre production de chlorophylle.
• Couleur de la jeune végétation « vert fluo ».
• Perturbe la croissance et l’assimilation de l’azote.
• Plus visible (couleur vert pâle) sur les jeunes pousses. Tend à disparaitre avec le vieillissement de la plante.
• Couleur très pâle des fleurs.

Rôle du soufre

• Participe à la production d’acides aminées essentiels et dans l’activation des enzymes liés à la croissance.

Pertes racinaires

• Réduction très importante du poids des racines : 57%.

 Carence en Phosphore

Symptômes 

• Cladodes des vieilles pousses plus foncées et qui finissent par tomber
• Dessèchement et chutes des cladodes des bouts des tiges, en cas de carence sévère.

Rôle du phosphore

• Elément de construction des acides nucléiques et de transfert de l’ATP.
• Joue un rôle de maintien dans la structure cellulaire.
• Favorise la floraison et la fructification.

Pertes racinaires

• Non mesurée.

Carence en Calcium

Symptômes     

• Chlorose et nécrose des jeunes pousses.
• Augmentation de la production de graines, mêmes pour les variétés mâles.
• Organes et racines raccourcis.
• Mort des jeunes pousses, avec productions de nouvelles pousses qui meurent à leur tour en cas de carence sévère.

Rôle du Calcium

• Stabilisation et construction des parois cellulaires.
• Influence l’activité des enzymes en lien avec les membranes.
• Favorise la croissance racinaire.
• Nécessaire à la germination des pollens.

Pertes racinaires

• Non mesurée, mais réduction visuelle importante.

Carence en manganèse

Symptômes

• Jeunes pousses chlorotiques et nécrosées.
• Jeunes pousses vertes et flétries.
• Déformations inhabituelles des pousses latérales.
• Décoloration blanchâtre des pointes des cladodes.

Rôle du manganèse

• Important pour la photosynthèse et la formation des chloroplastes.
• Favorise la production des jeunes racines latérales.
• Active la croissance en influençant la croissance en longueur des cellules.

Pertes racinaires     

• Poids des racines non affecté.

Carence en Zinc

Symptômes 

• Entre nœuds raccourcis et distance entre cladodes fortement réduite.
• Nanisme, pousse en forme de rosette.
• Coloration foncée des cladodes.

Rôle du Zinc

• Elément de constitution des enzymes, qui jouent un rôle majeur pour la photosynthèse, le métabolisme respiratoire, la synthèse des protéines et la production des substances de croissance.
• Influence la production d’acide 3 acétique, important pour la croissance.

Pertes racinaires

• Réduction significative du poids des racines : 32%.

Carence en Bore

Symptômes

• Visibles sur jeunes et vieilles pousses.
• Sur jeunes pousses : flétrissement brusque des extrémités, suivi d’un dessèchement et de la mort des cladodes.
• Sur vieilles pousses : cladodes courts et nécrotiques.

Rôle du Bore

• Favorise la croissance en longueur des cellules et la stabilité des parois cellulaires.
• Favorise la production de sucres.

Pertes racinaires

• Réduction significative du poids des racines : 21%.

L’évolution génétique, l’apparition de nouvelles variétés et l’optimisation des techniques culturales de ces dix dernières années, posent la question de l’actualité des références établies en matière d’alimentation minérale de l’asperge par Morse en 1916; Born en 1979, Follett en 1984, Benson et Paulsen en 1990 , Hartmann et Warman en 1991, puis Bergman en 1993.

De nouvelles références pour quatre éléments

Aujourd’hui, les derniers travaux du Dr C. Feller et d’A. Müller du Leibniz Institute of Vegetable and Ornamental Crops, à Großbeeren en Allemagne, complètent et corrigent les travaux réalisés 12 ans plus tôt. Ces travaux ont été réalisés pendant deux années consécutives (2013 et 2014) selon une méthodologie permettant d’induire des carences et d’en évaluer les impacts. (voir encadré 1)

Aux vues des résultats (voir taleau 1), les références établies par Bergmann en 1993 restent d’actualité. Pour le Magnésium, elles sont comprises entre 0.15 à 0.30 %. Pour le Soufre elles sont supérieures à 30 ppm et pour le Zinc entre 20 à 60 ppm.  En revanche, les références analytiques établies par Bergmann en 1993 doivent être augmentées. Pour le Calcium, elles passent de 0.40 % à plus de 0.80 %, le Potassium de 1.5 à 2.5 %. Pour le Bore, la référence de 50 ppm augment à plus de 150 ppm et celle du Manganèse de 75 à plus de 100 ppm. Ces valeurs établissent ainsi de nouvelles références pour ces quatre éléments.

Un véritable impact sur le potentiel productif

Au-delà des conséquences sur la fonction chlorophyllienne (perte de surface foliaire), les résultats de cette recherche mettent en évidence la perte de masse racinaire, organe majeur de stockage des réserves glucidiques (voir ci-contre). Hormis la carence en manganèse, toutes les autres carences ont un impact majeur sur la réduction du volume et du poids des racines. Dans l’ordre, la carence Magnésienne (Mg) et Soufrée (S) sont les plus significatives avec une perte de masse racinaire de 60 et 57%. Viennent ensuite le Potassium (K), le Zinc (Zn) et le Bore (B), avec respectivement 40%, 32% et 21% de perte. Elle n’a pas été mesuré pour le Calcium (Ca), mais reste visuellement significative. Bien souvent les symptômes de carence se confondent avec d’autres symptômes. Ils n’ont pas les mêmes origines et nécessitent un examen approfondi. Les causes peuvent être nombreuses : maladies, insectes, sècheresse, gel, phytotoxicité d’engrais foliaires ou d’herbicides. Aussi, les carences peuvent s’extérioriser de différentes manières : chloroses, nécroses partielles ou totales, couleurs des cladodes et des fleurs, déformations et nanismes plus ou moins importants. Pour un diagnostic certain, une analyse foliaire, complétée d’une analyse de sol est nécessaire. Le tableau des résultats « Analyse des rameaux et des cladodes », peut d’ores et déjà servir de référentiel.

Méthodologie des travaux du Dr C. Feller et d’A. Müller

Les asperges ont été cultivées pendant deux années consécutives (2013 et 2014). La 1ère année, les plants ont été cultivés en pots de 3l, remplis de terre. L’année suivante, ils ont été transplantés dans des pots de 12 litres, remplis de matière neutre (sable de quartz lavé). A compter de ce moment, les plants ont été fertilisés toutes les semaines à l’aide d’une solution nutritive contenant tous les éléments nutritifs essentiels, sauf celui qui entraînera la carence. Ils ont été comparés à un témoin normalement fertilisé. Les éléments manquants étaient soit le potassium (K), le magnésium (Mg), le soufre (S), le bore (B), le manganèse (Mn) ou le zinc (Zn). Les mesures ont été réalisées sur 3 variétés fréquemment cultivées en Allemagne (Gijnlim, Rapsody et Cumulus). En 2014, deux modalités supplémentaires induisant une carence en phosphore (P) et en calcium (Ca) ont été ajoutés sur la variété « Cumulus ». Ces deux éléments n’ont été examinés que visuellement. Pendant la culture 2014, tous les symptômes visibles de carence ont été enregistrées et photographiés. Fin 2014, les plantes ont été récoltées, puis analysées. Ces analyses ont été faites sur les cladodes, les rameaux et des racines. Elles ont été complétées par la mesure en degré Brix des racines (fin 2014).

Tab 1 Analyse des rameaux et des cladodes

ABSTRACT

In a context of genetic evolution of asparagus varieties and optimization of cultivation techniques, research work on the identification of asparagus deficiencies resumed in Germany in 2013 and 2014. This work confirms the references established by Bergmann for Magnesium, Sulfur and Zinc. They modify upwards (up to triple), the reference values ​​of Calcium, Potassium, Boron and Manganese. In addition, they highlight the diversity of deficiency symptoms and the risk of confusion with other causes. Also and as a major fact, they demonstrate the impact of severe deficiencies on the reduction of root mass (except manganese).

El espárrago por sí solo se ha posicionado como un ítem de prestigio y alta popularidad para todo tipo de consumidores. Si a esto le sumamos la condición de producto orgánico tenemos entonces un producto de demanda en continuo crecimiento.

Conceptos generales

Las preguntas más frecuentes entre los interesados en el manejo orgánico son ¿Cómo voy a reemplazar los agroquímicos necesarios para que mi cultivo sea rentable? ¿Conseguiré los mismos resultados utilizando productos orgánicos que agroquímicos convencionales?

Lo primero que hay que tener en cuenta es que no se trata de sustituir agroquímicos de síntesis con otros aprobados por los organismos correspondientes, se trata de un sistema completo y complejo de manejo del cultivo que involucra trabajar “en conjunto” con lo que la naturaleza nos ofrece para mantener el equilibrio y lograr producciones de calidad, en cantidad suficiente, sin producir contaminación de ningún tipo en el producto y en el ecosistema.

Una parte muy importante es tomar conciencia del hábitat que rodea al cultivo y cómo este nos puede ayudar en nuestro propósito. Vegetación autóctona, barreras naturales, topografía del terreno, condiciones climáticas, condición de los suelos, etc. Con respecto al cultivo en sí, lo importante es tratar de que la planta desarrolle por sí misma la mayor cantidad de defensas posibles de manera tal que las aplicaciones fitosanitarias sean solo como ayuda y no el único método. Las esparragueras que se desarrollen fuertes, equilibradas nutricionalmente, con la cantidad apropiada de agua y manejo adecuado de cosecha, estarán en mejores condiciones de resistir plagas, enfermedades y estrés. A su vez producirán la suficiente cantidad de espárrago como para que el cultivo sea rentable.  Cómo podemos lograr que todo esto ocurra? En primer término tomando conciencia que la agricultura orgánica es un sistema, no una receta y como tal hay que atender a todas las partes del mismo.

Manejo del cultivo

El espárrago es un cultivo que responde muy bien al manejo del agricultor. Esto nos da un plus con respecto a otros cultivos ya que todas las acciones que tomemos se manifestarán en el cultivo fácilmente. El espárrago orgánico tiene las mismas necesidades fisiológicas que un espárrago convencional. La forma de proporcionárselas será lo que deberemos adecuar para lograr la condición de orgánico.

Analizaremos los siguientes puntos:

Fertilización

La agricultura orgánica no centra la mayor importancia en los requerimientos de nutrientes de la planta, sino en la salud y fertilidad de los suelos. Fortaleceremos este concepto  para asegurar la nutrición de la esparraguera de acuerdo a sus necesidades y a la disponibilidad de nutrientes que un suelo sano pueda proporcionarle.

Lo importante es determinar la fuente de los diferentes nutrientes y las prácticas que podemos realizar para favorecer la fertilidad y sanidad del suelo. Las cantidades de nutrientes, estarán dadas por diversos factores inherentes a cada situación en particular (suelo, edad de las plantas, producción, etc.).

Las distintas prácticas que podemos realizar para favorecer la fertilidad del suelo son

• Asociaciones de cultivos o coberturas vegetales en los interfilares de la esparraguera. Siempre que se cuente con el agua suficiente, es una excelente práctica. Depende de las necesidades del suelo podremos consociar con leguminosas (inoculadas con rhizobium), cereales invernales, etc. esto también proporcionara al suelo la estructura necesaria para favorecer a los organismos benéficos. Estas asociaciones pueden ser temporarias o permanentes, cada agricultor verá la forma en que esta práctica le resulte más beneficiosa.
• Aplicar distintos tipos de compostas vegetales o animales, correctamente fermentadas, para evitar contaminación de suelo, agua o producto
• Aplicación de microrganismos
• Aplicación de minerales

Como en todos los casos, es importante contar con análisis de suelo y agua para saber en qué condiciones iniciaremos nuestro cultivo.

Igual que en cualquier  cultivo de espárragos, especialmente en el orgánico, la fertilización de pre siembra es fundamental para el éxito

La incorporación de una buena fuente de materia orgánica en cantidades adecuadas, no solo dará la nutrición necesaria a la futura planta sino que también creará las condiciones óptimas para la proliferación de microrganismos benéficos de los cuales hablamos anteriormente. Podremos aplicar composta animal o vegetal. Además será muy importante agregar en este momento la cantidad suficiente de mineral fosfórico y si es necesario K como sulfato que se irán biodisponibilizando. También cualquier tipo de enmienda  como por ejemplo yeso agrícola, sales calcáreas, o cualquier otra corrección que se requiera.

Es importante en este punto comenzar con la microbiología. Los microorganismos del suelo  ponen  nutrientes a disposición de las plantas (biodisponibilidad) a través de la descomposición de la materia orgánica y su reacción bioquímica con la porción mineral del suelo. Bacterias y hongos aeróbicos forman una relación simbiótica con las raíces de la planta proporcionándoles nutrientes fácilmente asimilables. Asimismo algunos, como las micorrizas, forman una capa protectora sobre la raíz que impide el ataque de patógenos. Otros   producen antibióticos naturales como la estreptomicina, que destruye patógenos del suelo. Hay algunos organismos específicos que protegen las semillas y las plántulas contra varias enfermedades, varias especies de bacilos, trichodermas y pseudomonas que protegen las raíces de las plantas contra enfermedades infecciosas.

Existen en el mercado varios productos con mezclas de estos microrganismos benéficos con los que deberemos inocular el suelo y luego dar condiciones para su proliferación. El suelo se compone de una cadena compleja de organismos. Su salud depende totalmente de que esa cadena se mantenga vibrante, activa y dinámica. En esparragueras ya implantadas podemos utilizar una serie de productos para mantener la fertilidad de nuestro suelo. Podemos utilizar fuentes permitidas de N, P y K así como también micronutrientes. También es importante el agregado de ácidos húmicos y fúlvicos por las muchas ventajas que estos ofrecen.

Control de plagas y enfermedades

Partiremos de la base que una planta fuerte y equilibradamente nutrida será capaz de lidiar más fácilmente con cualquier plaga o enfermedad que quiera atacarla. Cuando las medidas preventivas, que incluyen controles culturales y físicos, no son capaces de controlar poblaciones de plagas y enfermedades, la última opción es el uso de productos permitidos. El espárrago es un vegetal naturalmente rústico y con gran capacidad de adaptación lo que hace que sea bastante simple manejarlo de forma orgánica. El monitoreo regular y sistemático de la esparraguera  va a proveer de información acerca del estatus tanto de las poblaciones de plagas como de benéficos. Debemos saber identificar cuales  son plagas, cuales son benéficos, y cuales son neutrales,  sus ciclos de vida  y qué comen cada uno de ellos. También nos permitirá evaluar si las medidas aplicadas para su control están dando el resultado esperado. Si es posible, hay que elegir cultivares de espárrago que sean resistentes a algunas de las principales plagas y enfermedades en su área. Identificar el daño  temprano en el ciclo del cultivo, es una forma efectiva  para reducir las poblaciones de plagas  y el daño producido por ellas. Los insectos también pueden ser vectores de enfermedades, por lo que reconocer los síntomas de enfermedades comunes  es fundamental para que el control sea integral. El manejo orgánico de plagas puede incluir trampas (feromonas, adhesivas, de agua, de luz) la liberación de insectos benéficos, el uso de cultivos trampa, y otras técnicas agronómicas aprobadas para la producción orgánica.

El control de las enfermedades seguirá las mismas reglas. Prevención, observación y control integral. El uso de pesticidas es un último recurso en la producción orgánica, y deberán ser productos aprobados e incluidos en el listado de productos permitidos. Pueden ser extractos de vegetales como piretrinas, neem, cítricos, chiles, etc. Productos minerales como azufre, cobre, arcillas, silicatos, caolín, aceites, jabón de potasa, etc. La utilización del pirodiservo es de gran ayuda en lugares donde esté permitido el uso de fuego.

Control de malezas

No hay muchas opciones para el control de malezas, lo más seguro es el control mecánico o manual. Tener en cuenta que las malezas, bien llevadas, pueden ser un aliado en contra de plagas y enfermedades. En plantación se puede utilizar acolchados plásticos biodegradables para dar tiempo a la pequeña plántula a desarrollar fuerte y sana hasta poder competir con las malezas de forma efectiva. Existen herbicidas orgánicos pero no son selectivos y a veces tampoco muy eficientes.

Riego

El manejo del riego en la esparraguera orgánica no difiere de la de sistema convencional. Lo haremos de manera tal de incorporarlo al sistema ecológico que hemos creado para permitir la salud del suelo y por lo tanto de la planta.

Conclusión

Como vemos es todo un sistema que tenemos que manejar, o más bien llevar a las condiciones de equilibrio que logren que nuestro cultivo se desarrolle en condiciones óptimas.

La agricultura orgánica es una forma de vida, una diferente forma de pensar y actuar, que nos aportará no solo un interesante beneficio económico sino también la satisfacción de estar colaborando con la salud del planeta.

Summary

Organic asparagus has the same physiological needs as conventional asparagus. It is how we meet these needs that we must adjust in order to achieve organic status. Organic agriculture places greatest importance on the health and fertility of soils. We need to strengthen these elements according to the asparagus’ needs and the nutrients present in the soil so as to ensure the plant receives sufficient nutrition.

It is assumed that a strong and well-nourished plant will be able to deal more easily with any pest or disease that wishes to attack it. Regular and systematic monitoring of asparagus will provide information about the status of both pest and beneficial populations. Such supervision will also allow us to assess whether the control measures applied are giving the expected results. If possible, choose asparagus cultivars that are resistant to some of the major pests and diseases in your area.

In italia, nel 2021, gli asparagi verdi e bianchi precoci hanno subito un’impennata delle richieste per via di una serie di situazioni legate alla scarsa presenza di prodotto proveniente oltre che dal Sud America (Messico e Perù), anche dalla Spagna a causa dall’andamento climatico avverso caratterizzato da temperature fredde che di fatto hanno ritardato le raccolte in molte aree d’Europa.

Uno specifico cavo elettrico isolato

A Bosco Mesola, in Provincia di Ferrara, una zona molto vocata  per la coltivazione dell’asparago in cui si coltiva l’Asparago Verde di Altedo IGP, Davide Zanellati, un giovane imprenditore, socio della Coop Casa Mesola, con la collaborazione agronomica dello scrivente e della ditta Ener Green di Piacenza che si è occupata della progettazione dell’ impianto elettrico, ha realizzato nel 2020 una asparagiaia della superficie di poco inferiore a 1 ettaro dotata di un impianto di riscaldamento basale funzionante a corrente elettrica. Un secondo ettaro, sempre nella medesima azienda è in via di preparazione e il trapianto dell’asparago avverrà nell’aprile 2021. Per la coltivazione realizzata nel 2020 si è preferito distanziare le file a 3 metri ed è stata scelta una densità di circa 28.000 piante/ettaro. Questa asparagiaia dispone di un sistema di riscaldamento del terreno funzionante con l’ausilio di uno specifico cavo elettrico isolato posto alla profondità di circa 25 cm, che ha permesso di programmare la temperatura del suolo a livello dell’apparato radicale fra i 15 ed i 17 gradi, sufficienti, in questo 2021, per raccogliere e avviare la commercializzazione degli asparagi verdi a partire dai primissimi giorni di marzo, in linea con i tempi programmati.  Per poter valutare l’efficienza dell’impianto, nonostante la giovane età dell’asparagiaia, si è optato per la raccolta già dal primo anno. Tenuto conto della situazione, si sono raccolti turioni per soli 20 giorni, dall’1° al 20 marzo, per evitare di stressare troppo la coltivazione. Ai fini di una valutazione agronomica e produttiva, sono state poste a dimora quattro cultivar: Verdus, Magnus Vitalim e Vittorio. Per questa prova che consideriamo innovativa, l’energia elettrica è stata fornita attraverso uno specifico contratto dalla rete pubblica distributrice. E’ una tecnologia    che può rientrare anche nei sistemi produttivi innovativi che possono utilizzare gli incentivi pubblici dell’agricoltura 4.0.  Al momento naturalmente è presto per fare valutazioni economiche, visto che solo nei prossimi anni sarà possibile trarre conclusioni e fare valutazioni più precise circa i risultati produttivi e il mantenimento delle temperature a diverse condizioni ambientali rispetto a quella dell’inverno 2021 caratterizzato da temperature piuttosto basse e scarsa piovosità. Le esperienze maturate nella produzione dell’asparago riscaldato con acque calde ci hanno fornito comunque elementi significativi circa il risultato dell’attività in corso. Alla fine della raccolta programmata al 20 marzo sono stati raccolti 26 quintali di asparagi sulle 20.000 piante poste a dimora dei quali oltre il 70% erano di categoria extra.

Energia elettrica fornita da fonti rinnovabili

Per quanto concerne la tecnica di coltivazione adottata al momento dell’accensione dell’impianto e della erogazione del calore, si è preferito coprire le file con un film biodegradabile per ridurre la dispersione del calore e contemporaneamente limitare al massimo la presenza delle erbe infestanti. Le file dell’asparago sono state ulteriormente ricoperte con un piccolo tunnel del tipo Nantese utilizzando un film trasparente termico dotato di tasche per facilitare la raccolta. Una prima sommaria valutazione sui costi di installazione di impianti come quello descritto, che si prevede possa avere una durata di circa 10 anni, ci consente di affermare che l’investimento per riscaldare 1 ettaro di asparagiaia sia dell’ordine dei 30-32.000 euro. E’ evidente che per impianti di dimensioni maggiori si potranno avere economie di scala anche importanti. Nelle condizioni agronomiche descritte la potenza approssimativamente necessaria per il riscaldamento di quell’ettaro è di circa 70 kW. Non in tutte le condizioni di lavoro sarà necessario l’impiego dell’intera potenza nominale dell’impianto. I consumi giornalieri dipenderanno fortemente dalle condizioni climatiche in cui il sistema si trova a operare e cioè dalla scelta di coltivare in file singole o binate, dalla zona climatica in cui si realizzerà l’impianto, dalla tipologia di terreno e dalle tecniche colturali adottate che potranno incidere in modo significativo sulla potenza necessaria. Ugualmente il costo dell’energia può avere prezzi diversi se questa viene fornita da rete pubblica od ottenuta da fonti rinnovabili quali il fotovoltaico o altro. Una prima sintetica analisi nella situazione descritta e per l’annata in corso in cui si è operato in questo 2020/21 ci fa pensare che il costo per Kg di asparagi verdi raccolti e commercializzati nel periodo che va dal 20 febbraio al 20 aprile, possa variare da 5,5 euro/kg nel caso di una produzione di circa 6 tonnellate/ettaro per scendere a 4 euro/kg nel caso in cui la produzione raggiunga le 9 tonnellate/ettaro. I valori calcolati e stimati, comprendono le quote di ammortamento per l’impianto dell’asparagiaia, l’ammortamento dell’impianto elettrico riscaldante, delle spese per il collegamento alla linea pubblica di erogazione dell’energia elettrica, delle spese di gestione dell’asparagiaia (concimazione, irrigazione, manodopera, etc). Essendo l’impianto gestito in coltivazione diretta dal titolare dell’azienda sono state escluse dal calcolo le spese per i costi figurativi quali il del prezzo d’uso del capitale fondiario, gli interessi per l’uso delle macchine e attrezzature e del capitale di anticipazione.

Maggiori informazioni a Macfrut 2021

Naturalmente, come preannunciato, nel momento in cui è stato redatto questo articolo non è ancora stato possibile avere informazioni più precise su alcune delle spese e dei ricavi e quindi siamo ricorsi a dati certi e stime. Tenuto conto della situazione commerciale di questo 2021 in cui l’andamento di mercato dell’asparago è stato attivo, il bilancio è da considerarsi positivo. I lati positivi di questo sistema sono sicuramente da ricercare nella facilità d’uso, nei bassissimi costi di manutenzione dell’impianto, nella elevata affidabilità e sicurezza di erogazione dell’energia elettrica. Per il 2022, con l’obiettivo di affinare la tecnica dell’uso di questa fonte di calore e continuare le valutazioni agronomiche ed economiche, con molta probabilità disporremo oltre al nuovo impianto, di una serra coltivata ad asparagi con copertura fotovoltaica la cui energia prodotti servirà anche per l’alimentazione dei cavi riscaldanti. Gli asparagicoltori dei diversi Paesi produttori che intendono valutare questa tecnica dovranno fare i conti con i costi sostenuti nei loro paesi. I dati economici evidenziati fanno riferimento ai dati e costi in Emilia-Romagna In occasione di IAD International Asparagus Days che si terrà a settembre in concomitanza di Macfrut 2021 sarà possibile avere maggiori informazioni in merito.