HYDROPONIC CUCUMBER PRODUCTION USING URETHANE FOAM AS A GROWTH SUBSTRATE

Cucumbers (Cucumis sativus L. ‘Loeica’) were grown in a specifically designed urethane based recyclable plant growth substrate (UBS) and rockwool (RW) under a recirculating hydroponic production system to: 1) evaluate the performance of UBS in a greenhouse hydroponic production system, and 2) compare the effectiveness of two irrigation schedules on cucumber production using UBS. Plants were fertigated either by schedules 1 or 2. For irrigation schedule 1, plants were fertigated to an extent that 25% leachate was expelled from the RW slabs per day; and for irrigation schedule 2, plants were fertigated at a higher frequency throughout the day at a rate of 1.6 times the volume of schedule 1. Results showed that the UBS seedlings were significantly shorter and one leaf stage behind the RW seedlings during early stages of plant development. This setback in plant growth resulted in delayed flowering and ultimately affected cucumber production. The first USB cucumber fruit harvested was delayed by three days when compared to RW plants. Several weeks after transplanting, plants on UBS did catch up to plants on RW in terms of leaf number and plant height. Eventually, over a 27 day harvest period there was no significant difference in cucumber production or quality between plants on these two growth substrates in terms of fruit length, circumference and total fresh weight. However, irrigation schedule 2 produced significantly more fruits than schedule 1. There was no significant difference in fruit weight per plant between the two substrates under watering schedule 2. The results of this study confirmed that irrigation is extremely important for crop production and that with some design modifications there is potential for the UBS to evolve into a competitive plant growth substrate for greenhouse soilless crop production. INTRODUCTION As the demand for greenhouse commodities increases, so does the demand for environmentally friendly plant growth substrate. Presently, the most commonly used soilless plant growth substrates are either non-renewable resources, such as peat moss (Wilson and Stoffella et al., 2003), or non-biodegradable or non-recyclable materials, such as rockwool (RW) (Hardgrave, 1995). RW has proven to be a good growth substrate but still has several issues related to disposal costs considering this material does not breakdown (Hardgrave and Harriman, 1995). Recently, a company in Ontario, Canada developed a urethane based recyclable plant growth substrate (UBS) specifically designed as an alternative for some of the non environmentally friendly growth substrates. Greenhouse growers and researches have been experimenting with foam growth substrates for years with some level of success (Cook, 1971; Benoit and Ceustermans, 1986; Wagner and Wilkinson, 1991). One of the advantages that this UBS has over its past foam relatives is that it was specifically designed as a growth substrate instead of being reclaimed foams from industrial waste products (Wees and Donnelly, 1992). When working with any growth substrate careful control of water and nutrient management is essential in order to maintain optimum growing conditions (Wakoh and Haggett, 1996). By modifying leachate fraction (LF) experiments from (Schon and Compton, 1997), 2 irrigations schedules were developed and tested to evaluate the performance of UBS in a recirculating hydroponic production system. The objectives of this study were to evaluate the performance of UBS in a greenhouse hydroponic production Proc. IS on Soilless Cult. and Hydroponics Ed: M. Urrestarazu Gavilan Acta Hort. 697 ISHS 2005 140 system, and compare the effectiveness of two irrigation schedules on cucumber production using UBS. MATERIALS AND METHODS Cucumbers (Cucumis sativus L. ‘Loeica’) seeds were sown in vermiculite filled UBS (10cm X 10cm X 6.5cm) and RW blocks (10cm X 10cm X 6.5cm). This was done to provide a uniform germination across treatments. All substrate (blocks and slabs) were saturated with nutrient solution for 24hours prior to sowing and transplanting. Once the seeds were sown, the blocks were placed under plastic tents for two days. After germination had started the tents were removed and a fertigation system was implemented supplying cucumber plants with a starter nutrient solution (as recommended by Ontario Ministry of Agriculture, Food and Rural Affairs (OMAFRA); EC and pH were adjusted to 2.5-3.0mS/cm and 5.8 respectively). Seedlings were watered as required. Once the seedlings had reached the 4-5 true leaf stage they were transplanted onto their respective UBS (90.5cm X 15.3cm X 7.5cm) and RW slabs (90.5cm X 15.3cm X 7.5cm). Plants were fertigated either by schedules 1 or 2 in a recirculating hydroponic production system. For irrigation schedule 1, plants were fertigated to an extent that 25% leachate was expelled from the RW slabs per day (Compton and Schon 1997); and for irrigation schedule 2, plants were fertigated at a higher frequency throughout the day at a rate of 1.6 times the volume of schedule 1 (established from past water holding capacity comparison experiments between RW and USB). Leachate was collected once a week and watering frequencies were modified accordingly. The nutrient recipes changed from Starter Feed, to Normal Feed, and finally Heavy Fruit Load (see Table 1) as directed by the plants growth performance. Each cucumber plant was trained to grow vertically by winding it around a suspended string. Axillary shoots from the first 5 nodes of the main stem were removed, as well as any other vegetative shoots along the main stem. This experiment was conducted at the research greenhouses at the University of Guelph, Canada during April to June 2003 under natural photoperiods. Continual plant height, leaf number (measured until plant height reached the top of the support strings), flower number (measured from first flower to first fruit harvested), fruit yield, and quality were monitored throughout the experiment. Fruits were harvested once they had reached the proper shade of green, and had achieved marketable size. Fresh weights were measured at harvest; the fruits were dried at 65°C in order to obtain dry weights. At the final harvest, leaf area was measured by a leaf area meter (LI-3100; LI-COR, Lincoln, Neb.) and roots were examined visually. This experiment was a randomized complete block design consisting of 3 blocks and 4 treatments with 15 plants in each treatment. The cucumber seeds were sown April 1 2003, transplanted on Day 14 (April 14 2003), the first flowers opened on Day 25 (April 25 2003), the first cucumber fruit was harvested on Day 44 (May 14 2003), and the final harvest was conducted on day 71 (June 1