a soilless strawberry crop
Résumé
La culture hors-sol du fraisier est de plus en plus populaire en Europe, principalement suite aux problèmes de pathogènes dans les sols et de recrutement du personnel. Au Canada, ce type de production en est à ses débuts et les paramètres de culture doivent être adaptés pour le climat et les conditions régionales. Trois expériences ont été menées dans la région de la ville de Québec pour identifier parmi les substrats disponibles localement ceux qui seraient les plus adaptés pour le fraisier, pour cibler la régie d’irrigation adéquate de chaque substrat et pour déterminer la conductivité électrique (CE) idéale de la solution nutritive appliquée. En plus de la fibre de coco (Coco) et d’un substrat à base d’écorces vieillies (Ecorce DE), deux substrats de sciure-tourbe ont été testés, un possédant une forte proportion de sciures (PA40) et l’autre en contenant moins (PA25). Les résultats montrent que les substrats Ecorce DE, Coco et PA25 ont le même potentiel de production, mais que l’implantation des plants dans le substrat PA25 est plus critique. Le substrat PA40 s’est révélé peu adapté pour le fraisier, probablement dû à l’immobilisation des éléments nutritifs par la sciure de bois. Pour tous les substrats, une régie humide (irrigation démarrée de -1,0 à -1,5 kPa) favorise la croissance et la production de fruits des plants, par rapport à une régie sèche (irrigation démarrée de -1,5 à -2,5 kPa). Finalement, la CE recommandée d’irrigation de 1,0 à 1,5 dS m-1 est adéquate pour le fraisier hors-sol et son augmentation n’a aucun effet sur la
Abstract
Soilless strawberry crops are getting popular in Europe, mainly because of soil pathogens and staff recruiting problems. This type of production is beginning in Canada, but the crop management parameters must be adjusted for the climate and the conditions of this region. Three trials were conducted in the Quebec City area to identify the most promising locally found substrates for strawberry, to find the appropriate irrigation management for each substrate and to determine the proper EC for the applied nutrient solution. In addition to a coconut fiber substrate (Coco) and an aged bark substrate (Ecorce DE), two peat-sawdust substrates were tested, one with a high proportion of sawdust (PA40) and the other with less sawdust (PA25). The results show that Ecorce DE, Coco and PA25 have the same productivity potential, but that strawberry plant establishment is critical in the PA25 substrate. The PA40 substrate is not appropriate for this crop, probably due to the nutrient immobilization by the sawdust. For all the substrates, wetter conditions (irrigation started at -1.0 to -1.5 kPa) enhance plant growth and fruit production compared with drier ones (irrigation started at -1.5 to -2.5 kPa). Finally, the recommended irrigation EC of 1.0-1.5 dS m-1 is appropriate for soilless strawberries; increasing it does not affect the crop and brings
Introduction
Strawberry is one of the most popular fruit in the world and is produced almost on every continent. In some regions, this crop is affected by soil pathogens, like Phytophtora spp. and Verticillium spp., and the use of methylbromide is gradually banned worldwide (Lieten et al. 2004). In addition, hard working conditions associated with the conventional cultivation of strawberries make it difficult to recruit staff (Ancay et al. 2010). For these reasons, many producers have found advantageous to move on to soilless culture, especially in Europe.
Many substrates are available for soilless culture, and the choice is made based on physical/chemical characteristics, costs and ecological concerns. Widespread in many soilless crops, coir is an organic substrate made with waste products of the coconut industry. Coir is mainly exported from Sri Lanka, Vietnam, India, Philippines, Mexico and Ivory Coast (Maher et al. 2008). The quality of the product and its properties may considerably vary from one supplier to another, depending on the process used (Evans et al. 1996; Abad et al. 2002). Coir sometimes contains high levels of sodium, chloride and potassium that need to be leached with a calcium nitrate solution before planting the crop. Sawdust is a wood industry by-product easily available in Canada at a low cost. Mixed with peat, it constitutes a substrate with interesting physical properties. Tested in a greenhouse tomato crop, this peat-sawdust substrate showed a high productivity potential with suitable irrigation management (Lemay et al. 2012). However, sawdust nutrient immobilization properties (Vano et al. 2011; Tilston et al. 2009; Szili-Kovács et al. 2007) and its limited water availability (Allaire et al. 2005) can limit growth and fruit production. Jarosz & Konopinska (2010) have obtained lower strawberry yields with a peat and pine sawdust (ratio 1:1) substrate compared to a peat and a peat-bark substrates. Naasz et al. (2009) found that apparent phytotoxicity of some barks may be related to insufficient aeration caused by microbial activity. Also, peat-sawdust substrates present risks of salt accumulation (Létourneau 2010). Therefore, peat-sawdust substrates may possess a great productivity potential, but only with appropriate particle size distribution and irrigation management.
Tensiometer based irrigation is widely used for many crops, both in the fields and in soilless cultures. This irrigation management type must be adjusted for each crop and substrate, to optimize its benefits (Shock & Wang 2011). In a greenhouse tomato crop, this irrigation system has resulted in higher yields (Lemay et al. 2012). As tensiometers are particularly suited for soils with a high water content (Durner & Or 2005), they are compatible with soilless culture, where the soil water tension is generally maintained in a range of 1 to 6 kPa (Shock & Wang 2011).
Fertigation is crucial in the management of a soilless culture, and the EC of the irrigation solution is the parameter used to control it. Applied EC recommended by the soilless strawberry CTIFL production guide (Guérineau et al. 2003) is 0.6-0.8 dS m-1 at planting,
increasing progressively at 1.5-1.6 dS m-1 until first flowers. CTIFL recommended EC is
1.0-1.8 for the flowering period and 0.8-1.5 dS m-1 at the fruit production, depending on
climatic conditions. However, Sarooshi & Cresswell (1994) reported that Australian growers use solutions of 2 dS m-1. Worldwide, a lot of studies are made on NaCl salinity,
and the results are sometimes contradictory. Keutgen & Pawelzik (2007) found an increase of fruit quality parameters in presence of a moderate NaCl salinity (40 mmol L-1), but most
of studies report damages to strawberry plants at EC solutions from 2.6 to 8 dS m-1 (Saied
et al. 2005; Ondrašek et al. 2006). It is therefore possible to think that strawberry plants are sensitive to a NaCl salinity and tolerant to other forms of salinity induced by high ionic concentrations (sulphate, potassium, carbonate).
The goals of this study were to identify the best organic substrates and their appropriate matric potential for the strawberry soilless culture, to try these parameters in a commercial context, and to find out the suitable irrigation solution EC for this crop. There is also interest in evaluating the productivity of locally produced low cost peat-sawdust substrates for strawberry crops in Quebec.
Materials and methods
This study includes three experiments: Spring of 2011, Summer of 2011, and Spring of 2012.