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For the production of green asparagus, the use of plastic films meets different objectives to those of the production of white asparagus. In the case of green asparagus, only transparent films are used, as the spear needs light to produce chlorophyll (green) or anthocyanins (violet, purple). This film is placed on arches to create a tunnel where asparagus can grow.  The precocious effect is sought by a warming of the soil that allows the plant to “wake up” earlier. For this, it is important to use a plastic with high thermal properties that will retain the calories at night which were stored during the day, as proposed by the company Europlastic. But the benefits of a plastic cover are elsewhere. The first step is to protect asparagus from the effects of climate, wind and rain, to improve its uprightness and visual appearance in order to obtain a premium quality.

Smoothing out temperature extremes

The plastic tunnel therefore acts as a mini-greenhouse. This protected area enjoys more moisture than the exterior air and is conducive to the quality of the asparagus. On the other hand, this small volume of air can quickly turn into an oven, reaching very high (or even too high) temperatures. In fact, in plots of green asparagus, films are usually removed in the morning and then replaced in the evening, which requires a lot of manipulation. To limit this labour time, film manufacturers offer a variety of solutions to avoid rising temperatures during the day. Europlastic offers a film which acts as a filter for short wave infrared radiation which is the source of the increase in temperatures. Daios uses the reflective power of ceramics added in a translucent film to reflect 30-40% of non-visible infrared rays. The aim of these films is to maintain the plastic cover for the duration of the crop by levelling out extremes in temperature. It is then possible to use harvest assistance machines in the same way as for green asparagus. The film is lifted and then replaced at harvest time, avoiding additional handling and reducing labour time. Another positive effect is that the tunnel becomes an enclosed space, which protects asparagus from diseases and pests, especially the asparagus beetle that has been on the rise in recent years.

 

The use of plastic cover films has brought asparagus cultivation into a new area. In the 1980s, a few microns of clear thermal plastic first warmed the soil more quickly to gain precocity, and then the widespread use of black/white pocket plastics in the 2000s profoundly changed production techniques. Today, the use of arches and the combining of plastics mean that production can be managed according to the meteorology, the production slots targeted, the availability of labour and market prices.

 

A “temperature comfort range”

But plastic films are first and foremost used as a way to improve the yields of an asparagus crop. According to data compiled by Christian Befve, an asparagus consultant, each plastic and plastic combination brings a gain in production. They all allow yields to be doubled (see GRAPH 1). Plastic films act first on the temperature of the soil. The rise in temperature depends on the ambient temperature but especially on the sunlight and the intensity of the light that passes through the thermal mulch. Temperature is a decisive factor in the growth of asparagus. Physiological data indicate that asparagus wakes up when the temperature reaches 11 degrees at 10 cm below the root plateau for early varieties (Darlise, Vitalim etc), 12 degrees for mid-season varieties and 13 degrees for late varieties. Temperature also has a direct influence on productivity. At the beginning of the season a degree Celsius gained starting from when the plant wakes means an extra 30 kg/ha/day harvested, in mid-season it is 10 kg/ha/day. On the other hand, if the temperature exceeds 25 degrees C at 10 cm below the plateau, the yield can drop in the order of 10%. At above 35⁰C, production activity is almost nil.

The temperature in the mound is very important for the growth of asparagus, for the quantity harvested and the quality of the spears. According to established data, the asparagus must be in a “temperature comfort range” of between 18 to 20 degrees Celsius at 20 cm below the top of the mound. Below this, the asparagus grows little. Above, spear quality problems appear (pinking, flowering). The data provided by Engels Machines show that it is possible to regulate the temperature of the mound by managing the different plastics and their positioning. The management of plastics is conducted according to the temperature of the mound. This management is subject to different influences and depends on a variety of objectives: desire for precocity, reduction of production peaks, spread of production, regularity of quality, etc. and better management of the workforce.

 

Playing with different configurations of films

 

The increase in temperature in the mound is related to the radiant heat reaching the mound. This can be modulated in different ways. Engels Machines has defined 6 installation combinations of three mulch films that can influence the temperature increase in the mound. Taking 100 as a base for the mini-tunnel+black plastic configuration, graph 2 shows a decreasing gradient of the thermal effect of different combinations. It can be noted that in all cases the white face reduces the thermal effect of the sun exposure the most. But it cannot be said that it cools the mound. This management of the various plastic covers can be carried out during the harvest with assistance machines with no additional working time. Regulation of the mound temperature requires forward planning by observing the temperature in the mound and taking into account the future climatic parameters (temperature, sunshine, rain, etc.). So Engels Machines has defined the management criteria and offers a plastics management service. It shows that it is possible to moderate the temperature of the mound in the plant’s comfort zone, 18 to 22 degrees Celsius, by adjusting the different configurations of the films (see Graph 3). According to Tom Smolders of Engels Machines, who worked on establishing this data, a more stable temperature over 24 hours reduces the percentage of hollow stems. This qualitative problem occurs when the temperature difference between the top of the mound and the root plateau is greater than 4^oC. The different plastic films are not only for gaining in precocity. On a late variety (eg Backlim) it is also possible to use a combination of high-performance film to group production and limit the harvest period in order to lengthen the growing period of the plant.

 

“Compromise solutions” between precocity and use

 

Given the strategic importance of plastic films, manufacturers have expanded their range with increasingly specific and technical films.  The thickness of the films is increasing the main reason for which is the direction of laying on the arch. According to Daios, the film placed perpendicularly requires a thickness of 50 microns to ensure their maintenance. On the other hand, a film placed parallel to the arch must be of greater thickness of 70 microns. With the development of harvesting machines, this mini-tunnel technique is being widely developed because it allows the use of two plastic layers without increasing the time devoted to the laying and lifting of films. While the covering and uncovering of films placed perpendicular to the arches increase harvest time by 30%. The race for the precocity brought about by the use of plastic films comes at a cost.  It is quantified by adding the costs of plastic films, the depreciation of the arches and harvesting machines, the cost of refilling pocket films (estimated at 0.12 euros in France), laying and lifting, storage, etc. and the cost of recycling, which will only increase.

In response to this, some manufacturers offer “compromise solutions” between precocity and ease of use by welding together a black/white pocket plastic film and a thermal plastic one. This double film creates an air space between the black/white film and the thermal film that acts like a mattress and allows the mound to heat up.  This double film can be placed on arches with a new insulating effect between the film and the mound. This area permits the condensation of moisture from the area to re-humidify the mound. According to Europlastic, the manufacturer of this film, the thermal film is enriched with UV stabilisers in order to increase its lifespan and make it equivalent to the black/white cover. The two films used together also have better resistance to handling that extends the life of the cover. Additionally, at the time of set up it requires one single filling of the pockets.  It also means less rolls in storage post-harvest. So Europlastic is talking about an economical film.

GRApH 1 PLASTIQUE source C.befve

In its range of mulch films, Reyenvas offers a 7-layer film using technology to incorporate a thermal layer inside the black-white film.  Combining these properties gains 3 to 5 days of precocity compared to a conventional black/white film. This unique film limits the cost of refilling pockets, handling, and then storing.  The 7-layer film is thicker (175 microns) and more resistant. There is a tendency evolving towards thicker films that will also be more resistant. Their lifespan will be extended to provide a partial solution to the plastic recycling problem. The lengthening of the film life, also offered by Daios, increases the years of film depreciation and reduces the cost of recovery taxes and disposal difficulties.

GRAPH 2 6 configuration Percentage

It is becoming desirable for plastics to be more discreet. For this reason, manufacturers such as Daios and Reyenvas offer green/white films to better integrate into the landscape. According to Daios, these films would also provide temperature gains compared to black/white film.

GRAPH 3 Effect foil management

 

More Info

Controlling with plastics

Early production: planting an early variety at shallow depths with several plastics and mini-tunnels

Late production: plant a late variety at depth and cover with white plastic

Grouped production: regulate the temperature of the soil at the root plateau (between 18 and 21 degrees Celsius) depending on the variety by managing the different plastic films

Spread-out production: plant several varieties at different depths and use several combinations of plastic films

Anticipating to limit temperature

Black mulch heats up more than white. White mulch limits the temperature in the mound despite a slight increase in temperature. It doesn’t cool the mound. It is therefore necessary to anticipate the changeover of face well before temperatures in the ground become too high. To regulate the temperature of the mound moderately, after the black plastic + tunnel it is better to use the white face and keep the other plastic on the tunnel, rather than take the plastic off of the tunnel and keep only the black. This second technique causes too great a temperature range in the mound.

Plastic and quality

The quality of the asparagus is made in the mound and on the mound. The use of plastics plays a big role in the quality of crops.

In the mound: It is important to limit the temperature range, between 18 and 21 degrees Celsius depending on the variety, to prevent the asparagus tip from flowering and to keep its tip closed.

On the mound: the temperature on the surface of the mound, and under the plastic, can get very high (60^oC) causing the tip to burn. To reduce the losses due to this problem, harvesting must be done early in the morning, the plastic blanket must be turned white face on the outside. It is possible to place hoops very close to the mound that create an air cushion between the mound and the black/white plastic.

 

 

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

 

Résultats en % ou ppm sur Matière Sèche	% Calcium	% Magnésium	% Potassium	% Soufre	Bore (ppm)	Manganèse (ppm)	Zinc (ppm)
Valeur du TEMOIN	0.87	0.20	2.78	0.39	163	81	21
Sans Mg	0.62	0.05	2.92	0.31	140	72	27
Sans Mn	0.82	0.19	2.45	0.36	163	62	20
Sans K	1.51	0.42	0.42	0.34	203	140	31
Sans Zn	0.91	0.21	2.72	0.41	170	77	18
Sans B	0.82	0.20	2.68	0.41	31	83	22
Sans S	1.02	0.26	2.69	0.20	217	120	25
Ref. Bergmann 1993	0.40 à 0.80	0.15 à 0.30	1.5 à 2.4	> 0.30	40 à 100	25 à 100	20 à 60

 

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.

 

 

Over the last decade, consumer awareness of the agricultural use of pesticides around the world has greatly increased. This new reality has intensified the need for solutions to reduce our reliance to chemical pesticides. What if we could monitor and anticipate the arrival of pests and diseases before any sign of them in the field? Could we choose the best treatment and the most appropriate moment for spraying, considering in which conditions it will evolve? All this is essential to optimize fungicides applications, avoiding unnecessary treatments and, perhaps, moving forward toward a more sustainable production system.  The spore trap is a device that anticipates fungal risks before visible signs of disease appear on plants in a given region. In fact, like pollen, a spore is a reproductive cell invisible to the naked eye which, carried by the wind, is deposited on the plant of the crop of interest. Its development gives place to the growth of fungal diseases such as rust (Puccinia asparagi), and purple spot (Stemphylium vesicarium) in asparagus. Currently, management strategies for these diseases are based essentially on visual observations in the field, guessing the best timing of fungicide applications. However, we already have all in hands to set up this method of integrated pest management in our own fields.

Purple spot and asparagus rust are well suited for spore sampling monitoring, because of their dispersion mode, spores coming from the crop residues at the surface of the soil. In this way, spore sampling, using the device installed near the ground, is at the forefront of capturing any spores that may emerge from the residues. There’re many different types of spore sampling devices available and suited for different usage, each with their strengths and their weaknesses. In Québec, Canada, we decided to use Rotorod-type spore traps because of its relative universality. Sampling is conducted 3 days a week, with each sampling period being from 8:00 am to 2:00 pm. The device is working by solar energy and connected to a timer and a small motor, which makes turning an underlying bar at 2,400 rpm. Speed brings down two sticks from the bar by centrifugal force. Carried by the wind, the spore then adheres to the sticks integrated into the sensor in the field. After every sampling period, a spore count is performed for both diseases collected with the device. With the help of the team of Hervé Van Der Heyden, phytopathologist at Phytodata Inc. here in Sherrington, Québec, the count is made with a microscope. Knowing that each fungus has is own DNA profile, we can hope that in a near future we will be able to speed up the count by using the PCR method like it’s already used for other diseases in other crops like onions and potatoes. That way, once the sampling done, we can get a picture of what’s going on in the field within 24 hours. From there, with the help of the closest weather station, we can target the optimal time to apply an appropriate disease-control product and more importantly, only if needed.

The first trials conducted in 2019 is very encouraging toward a better integrated management of purple spot and asparagus rust. A spore-sampling network at a regional scale between a group of asparagus growers would enhance the usefulness of the system, providing a clear picture of the evolution of these diseases during the season and over the years. Combined with other decision-support systems like field scouting and weather-based forecasters similar to TOM-CAST used in North America, growers and crop advisors will be equipped for accurate decision making. At the key, a more precise positioning of the fungicide applications, leading to fewer sprayings, economy of scale, a more sustainable way of producing asparagus and improved social acceptability. During the next few years, we will work to optimize the use of the spore traps by evaluating what is the best height to capture spores depending on the period of the growing season because the location of the trap influences the number of spores captured and the threshold of intervention. We will also be working on understanding better the pattern of spore release which is essential to determining when and how long to sample to avoid underestimating the number of spores; how can we use this to detect Fusarium spp. and other diseases that can affect the asparagus and developing a network in the major growing zones in Quebec. Lots of possibilities and interesting perspectives to come!

Testimony

The grower’s experience 

Mario Rondeau, Asperges Primera, Green asparagus grower in St-Thomas, Québec, Canada

“The spore trap is a very interesting tool in reducing pesticides and improving the efficiency of phytosanitary treatment. It is still in development but very promising. We only have 1 year of experience with the sensor and the amount of information collected is important. With correlations with temperature, humidity, rains, etc., we will be able to predict the application period fairly well. We can also more clearly choose which mode of action of the fungicide suit best to the stage of development of the fungi as well. The use of the sensors will continue in 2020 with a lot of optimists!’’

The Lebourg family is based in Cestas in the south-west of France, where it runs an 800 ha farm on which asparagus is a diversification crop, with 35 hectares planted in 2017 and 2018. Here, ridge cropping is justified because the layer of “alios”, which limits the depth and drainage of the soil, is very close to the surface (40 or 50 cm deep). In 2018, the Lebourg family embarked on an “out-of-the-ordinary” project to make 70 cm beds in a semi-circle to follow the path of the watering pivot. The large gap between rows (more than 3.50 m) allows a large volume of earth to be brought into the bed. “And instead of planting 20 cm below the surface, we planted 20 cm above,” explains Philippe Lebourg.

Modify and raise all equipment

“Large beds allow for more regular production because they reduce temperature contrasts. The first spring harvests have been slightly delayed, but volumes are rapidly becoming more stable,” said Philippe Lebourg. In addition, the beds are covered with a double mulch: thermal mulch and tarpaulin. The planting was done in double rows at 30,000 crowns/ha, or 11 crowns per linear metre, mostly with Darzilla (70%), then Vitalim, Terralim, Cygnus and Prius. The biggest adaptation was to the hardware. “With beds 70 cm high, we had to modify and raise all of the equipment, from tractors to harvest assistance machines,” said Lebourg. The move to a large gap has reduced the costs of setting up the crop as well as harvesting costs. In fact, going from 2.50 m to 3.63 m reduces the length of beds per hectare by 45%, from 4,000 to 2,875 linear metres (ml). There is a direct saving on the purchase of hoops and plastics. This also applies to the cost of harvesting, where there is a 30% gain: less distance covered and more spears to harvest per metre improve the hourly yield of the pickers.

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Also in Morocco

Ridge cropping has also been tested in Morocco, in the region of Kénitra. The area has shallow sandy soils with a concentration horizon of 30cm.  In addition, the rise of the water table in winter creates unfavourable conditions for the roots, with the risk of fusarium.  This is why ridge cropping is practised on many crops, including fruit trees, mainly stone fruit, on raspberry and, of course, on asparagus.  Beds are made before planting to position the crowns 25-30 cm above point zero.   The technique has elicited great interest in the asparagus sector.  However, one limitation of the technique is the difficulty of making high beds for white asparagus production.  On the other hand, the technique i svery well suited to the production of green asparagus.

The production potential of an asparagus field is conditional on the volume of good soil available to the root mass of each plant. In a plot, the 0-20 cm horizon is the richest. In soil analyses, it is not surprising to find that this first part of the soil has 3% organic matter, while at a 40-60cm depth, the organic matter rate is only 0.2%. In some cases, the plant will be unable to use this deep horizon because it is too sensitive to rises in the water table or is composed of hard rocks.

 Between 25 and 30 cm above ground level

The raised bed technique can respond to different situations. The objective is to take the good earth from across the entire surface area of the plot and bring it back to the ridge. The ridges are spread well apart, at least 3.50 m, and can be 30 cm in height. The planting is therefore done at between 25 and 30 cm above ground level. In this way, the space that can be explored by the roots is twice as large as for a traditional plantation. Also, from the first year of planting, the roots of the young crop find there way down to a depth of 0.70 m because the soil is rich and aerated.  Usually, the roots only explore depths of up to 0.50 m. Ridge cropping also allows for natural drainage. Asparagus crowns are always found outside the wet zone during wet and rainy winters or springs.

During the ridging-up of the crop, the earth from the inter-rows is brought in to form ridges of 0.70 m in height. This large volume of soil, directly in contact with the thermal plastic, makes for a faster and more homogeneous warming of the ridge, which is 30-40% higher than normal. The extra heat stored allows for earlier and higher production, according to the ratio of 1^oC extra equals a harvest gain of 30 kg per hectare per day during the early period.  Ridge cropping also limits the raising of the crowns – the root plateau – which are already located in a comfort zone (aerated soil).

 Concentrate moisture at the foot of plants

Growing in raised beds requires a great distance between rows in order to have the maximum amount of soil for the ridge and then for the bed. This constraint then turns into an advantage. In fact, the reduction in the number of rows per hectare means that the density of plants per linear metre has to be increased with a double-row planting. Fewer rows per hectare also brings savings on mulch and hoops and therefore in labour for harvesting and time spent on all maintenance work. The elevation of the beds does not necessarily require specific equipment, but does demand some adaptation of the conventional equipment with modifications that some manufacturers can offer. Tractors must have more ground clearance to allow them to straddle the beds.  A higher bed also results in more exposure, resulting in faster drying. Plants will go deeper to look for moisture and compensate for some of this drying out. Localised irrigation is a must in order to concentrate moisture at the foot of the plants. About 10% more input will be required on the row and per hectare.  The technique developed in Peru by Christian Befve has now been adopted successfully in Europe, as Philippe Lebourg, an asparagus producer in the south-west of France, testified at the time of the IAD 2019 visits.