Supplemental Lighting in High-Wire Cucumber Production on Raised- Troughs

Transcription

1 Supplemental Lighting in High-Wire Cucumber Production on Raised- Troughs Xiuming Hao and Athanasios P. Papadopoulos Agriculture and Agri-Food Canada, Greenhouse and Processing Crops Research Centre 2585 County Road 20, Harrow, Ontario, N0R 1G0. Canada Keywords: lighting, cucumbers, yield, energy use efficiency, high pressure sodium lamps Abstract Consumers demand year-round production and supply of high quality produce. However, wintertime greenhouse crop production in northern regions is usually limited due to low solar radiation. A study was conducted over two years to develop a high-wire cucumber production system on raised-troughs with supplemental lighting for year-round production. It was found that the optimum fruit to leaf ratio for the high-wire cucumber grown on raised-troughs was 1:2. Supplemental lighting (44 W PAR, 17 hours per day (average), 2.6 MJ m -2 day -1 ), increased the fruit production in winter by more than 100%. The supplemental lighting system also provided 60-90% of the heat requirement by double-polyethylene greenhouses in the winter. Energy use efficiency (unit produce per unit of input energy) was higher with supplemental lighting from Nov. to Feb. (4 months). A preliminary economic analysis conducted based on the yield data from this 2-year of study and a preliminary energy analysis indicated that supplemental lighting in high-wire cucumber production may be economically feasible in Ontario, Canada. INTRODUCTION Consumers demand year-round production and supply of high quality produce. However, in northern regions such as Canada, low solar radiation (Fig. 1) has limited the production of greenhouse vegetables in the winter time. Due to the limitation imposed by the low natural light, Canadian greenhouse vegetable growers usually plant their crops in late Dec. or early Jan. and start to harvest in late Feb. and early March. Consequently, there is a period of two to three months during which practically no greenhouse vegetables are produced in Canada, without artificial light (Papadopoulos et al., 2002). To ensure a steady supply of greenhouse vegetables to meet the market demands and to maintain or increase market share, artificial light is needed to supplement natural light in the winter. Considerable research has already been conducted on supplemental lighting for use in greenhouse crop production in Canada (Dorais and Gosselin, 2002). Supplemental lighting improves greenhouse vegetable yield, and quality (Hao and Papadopoulos, 1999; Dorais and Gosselin, 2002). However, supplemental lighting has only been used in greenhouse vegetable production in Quebec where electricity has been more economical. Recent studies in northern Europe (Armstrong, 2001; Marcelis et al., 2002) and in Canada (Hao and Papadopoulos, 2002) have shown substantial yield increases with high supplemental light (e.g µmol m -2 s -1 ; i.e. 2-3 times of the light intensities used before), which has increased the interest in the use of supplemental lighting in greenhouse vegetable production. In Canada, greenhouse cucumber plants are usually trained to an umbrella system with a wire height of 2 meters; skilled workers are essential for managing such crops. The resulting uneven crop canopy with the umbrella system causes uneven light distribution, large fluctuation in production and poor fruit quality. The high-wire cucumber production system is a system in which the plants are trained to single stem, just like in greenhouse tomato production. With the high-wire cucumber training system, light distribution in crop canopy is much more uniform, which should lead to better yield and quality, and stable production. However, the system usually requires very high wires. Otherwise, the fruit touches the ground, causing it to bend, because the fast stem growth outpaces fruit Proc. IC on Greensys Eds.: G. van Straten et al. Acta Hort. 691, ISHS

2 growth. Also, the plants trained with the high-wire system show leaf chlorosis and lack of vigour when the fruit load is high or late in the season. Supplementary lighting has the potential to reduce inter-node length and increase the fruit growth rate. Raised-troughs can keep the fruit away from the ground when the plants are lowered and make it easy for inter-cropping. This paper reports key findings of a 2-year study to develop a high-wire cucumber system on raised-troughs with supplemental lighting; fruit pruning was also investigated in the study. MATERIALS AND METHODS Two greenhouse compartments (49 m 2 each), one with and one without supplemental lighting were used for the study. For the supplemental lighting treatment, high pressure sodium lamps (HPS, installed capacity of 170 W m -2 ), supplied 240 µmol m -2 s -1 PPFD (photosynthetic photon flux density, 44 W) to the treatment plants. The photoperiod for supplemental lighting ranged from 12 to 20 hours, depending on natural light intensity and plant growth stage. During the week following planting, light was supplied for 12 hours a day; then it was gradually increased to 20 hours a day when a full canopy had developed. Supplemental lighting started at 10 or 12 pm and stopped at 6 pm. The lamps were turned OFF when the natural global radiation exceeded 300 W m -2. During the 2-year study (Oct to Nov. 2003), three experiments or crops (winter, spring and summer/fall) per year were conducted. Plants were grown on the rockwool stubby slabs (20 cm 50 cm 10 cm) on raised-troughs at cm above the ground. Winter crops were planted at 2.5 plants m -2 in mid-october and terminated in late Feb. to early March. Spring crops were planted at 3.4 plants m -2 in March and terminated in July to August. Summer/fall crops were planted at 3.4 plants m -2 in August and terminated in Nov. The spring and summer/fall crops were intercropped in August Winter and spring crops were intercropped in Feb A total of 48 plants (excluding surrounding guard plants) in each lighting treatment were used for collecting plant growth and yield data in the winter crops while 72 plants were used in the spring and summer/fall crops. In the experiment that investigated the effects of fruit pruning on plant growth and fruit yield, four fruit/leaf ratios (1:1, 1:2, 1:3 and 1:4 fruit to leaf) were compared. There were a total of 36 plants (arranged into 2 plots) for each fruit pruning treatment in each greenhouse compartment. Increase in fruit production and change in relative light use efficiency were calculated for each month. A preliminary energy use analysis was conducted by using data from our experiments and energy use (hourly) profiles from commercial greenhouses. Energy use efficiency (unit of produce per unit of energy input) was also calculated for each month. RESULTS AND DISCUSSION Light, Fruit Production and Light Use Efficiency The photosynthetically active radiation (PAR) inside the greenhouse was substantially increased with the use of supplemental lighting, especially in Nov., Dec. and Jan., when it was more than doubled (Fig. 1). Supplemental lighting increased fruit yield in Nov., Dec. and Jan. by more than 100% (Fig. 2). In Feb., Mar. and Oct., fruit yield increased by more than 30%. There was little yield increase from Apr. to Sept. Fruit yield in July, the month with the highest natural light, was even reduced by the supplemental lighting. Relative light use efficiency, i.e. percentage of yield increase for each percent of light increase in Dec. and Jan. was higher than the standard 1%. However, there was no improvement in light use efficiency in the rest of the year. Fruit Pruning Among the 4 fruit to leaf ratios tested, the highest fruit yield was achieved with a fruit to leaf ratio of 1 to 2 (i.e. keeping one fruit at every other leaf, Table 1). Fruit yield 210

3 decreased with further reduction in fruit load (i.e. at lower fruit to leaf ratios), but fruit size increased. Energy Analysis and Energy Use Efficiency The estimated total energy delivered into the greenhouse was higher with the supplemental lighting than without the supplemental lighting (Table 2). When the momentary heat energy released from the lighting systems was higher than the greenhouse heating requirement, the greenhouse air temperature exceeded the heating set point. When greenhouse air temperature became higher than the ventilation temperature set point (24 C), excessive heat was vented out. In Oct., the heat released from the lighting system was much higher than the heating requirement; about 60% of this heat was vented out or contributed to non-essential heating (increasing greenhouse air temperature to above the heating set point); and, only about 40% of this heat made a useful contribution towards essential heating of the greenhouse. From Nov. to March, 60-80% of the heat released from the lighting system contributed to the essential heating requirement. Energy use efficiency improved with supplemental lighting in Nov., Dec., Jan. and Feb., while it decreased in the rest of the year (Table 2). Our calculations did not take account of the boiler efficiency. If the boiler efficiency (80%) were taken into consideration, the energy use efficiency in March would be slightly improved with the use of the supplemental lighting (data not shown). The economic feasibility of supplemental lighting strongly depends on the yield increase realized with supplemental lighting, the product market price, the energy cost, the interest rate, the cost of HPS system, and other factors. Based on the current condition in Ontario (i.e. $0.07/kWh electricity, $8/GJ natural gas, and interest rates of about 7%) and the data from our study, a preliminary economical analysis was conducted. We found that supplemental lighting was most economical during the 4-month period (Nov. to Feb.). With the supplemental lighting, 74 cents additional cost per additional cucumber is needed. When the period of the supplemental lighting was increased from 4 to 6 months (Oct. to March), the cost increased to 75 cents; reducing the period to 2 months (Dec. and Jan only) increased the cost to 97 cents. If all production costs were included, the cost for each additional cucumber with the supplemental lighting would be $1.1 to $1.3. In North America, cucumber market price is usually the highest in Dec. and Jan. and gradually decreases toward summer. Whole sale price is usually $1.3 to $1.8/cucumber from Nov. to Feb. Therefore, it should be economically feasible to produce cucumbers on raisedthrough with supplemental lighting from Nov. to Feb. in Ontario, Canada. Literature Cited Armstrong, H High productivity from intense lighting. Fruit & Veg Tech 1(2): Dorais M. and Gosselin, A Physiological response of greenhouse vegetable crops to supplemental lighting. Acta Hort. 580: Hao, X. and Papadopoulos, A.P Effects of supplemental lighting and cover materials on growth, photosynthesis, biomass partitioning, early yield and quality of greenhouse cucumber. Sci. Hortic. 80:1-18. Hao, X. and Papadopoulos, A.P Supplemental lighting substantially increased fruit yield of high-wire cucumber grown on raised-gutters in winter. Annual Report- Greenhouse and Processing Crops Research Centre, AAFC, Harrow, ON, Canada. Marcelis, L.F.M., Maas, F. M. and Heuvelink, E The latest developments in the lighting technology in Dutch horticulture. Acta Hort. 580: Papadopoulos, A.P., Demers, D.A. and Theriault, J The Canadian greenhouse vegetable industry with special emphasis on artificial lighting. Acta Hort. 580:

4 Tables Table 1. Effects of supplemental lighting and fruit/leaf ratio on fruit yield, size and #1 grade of cucumber cv. Bodega (March 27 to July 11, 2003)* Treatment Fruit: leaf ratio Marketable fruit Number (# m -2 ) Size (g fruit -1 ) % of z grade #1 1: ab b 88.2 a Ambient light 1: a a 91.4 a 1: b a 93.0 a 1: b a 91.4 a With supplementary lighting 1: a c 89.6 a 1: a bc 89.3 a 1: ab ab 91.4 a 1: b a 96.4 a *. Different letters in the column within the same light treatment indicated a significant difference between fruit pruning treatments (P < 0.05). Z Percentage of grade #1 fruit in marketable fruit (based on fruit number). 212

5 Table 2. An energy analysis for high-wire cucumber production on raised-gutters with supplemental lighting* With HPS supplemental lighting Energy use efficiency Greenhouse heat requirement Z (MJ m -2 ) Hours of lighting (HPS) Electrical energy (MJ m -2 ) Heat from heating system (MJ m -2 ) Total energy (MJ m -2 ) With HPS lighting (g MJ -1 ) Without HPS lighting (g MJ -1 ) Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec * Based on the data from the 2-year study and energy monitoring data from a commercial greenhouse. Z. Estimated from the energy monitoring data of a commercial greenhouse and the simulation results from ENPASS for Greenhouse, a computer software developed by Enermodel Engineering Ltd. (Waterloo, Ontario, Canada) and AAFC to simulate energy consumption in various types of greenhouses. 213

6 Figurese 25 Global solar radiation (MJ day -1 ) Solar Supplemental light 5 PAR (MJ day -1 ) Fig. 1. Average global solar radiation at Harrow, Ontario (top graph) and photosynthetically active radiation (PAR) inside the greenhouses (bottom graph, assuming 60% greenhouse light transmission and 45% PAR in solar global radiation). 214

7 Relative light use efficiency (%) Increase in total fruit weight (%) Fig. 2. Increase in total fruit weight in the greenhouse with supplemental lighting over the one without supplemental lighting (top graph) and change in relative light use efficiency (percent increase in total fruit weight per 1% increase in photosynthetically active radiation, PAR). 215

8 216