The use of infrared-reflective diffuse coatings results in a lesser need for ventilation during summer and thus a fewer loss of CO2 from the greenhouse. A saving of 20% C02 seems realistic to the researchers.
During a vast number of hours in spring, summer and autumn, Alstroemeria utilizes the natural daylight poorly to moderately; particularly above 200 W/m2 irradiation. This is due to a decreased opening of the stomata. This obstructs the C02 absorption of the leaf.
Controlling the stomatal conductance can thus result in a much higher daylight efficiency. In the Alstroemeria cultivation, the use of coatings and shading agents is uncommon. However, research shows there is often too much sunlight during the summer months. Also, growers confirm that there are no tools for climate control in the summer, so the cultivation regularly stagnates. In these circumstances, it may seem better to offer light for the benefit of a better climate.
Source: report Increased daylight utilization in Alstroemeria, Kas als Energiebron
In this research, the aim is to achieve this by using a warmth (infrared) reflective diffuse coating with a high degree of light transmission on the greenhouse roof in combination with a different form of climate control. The diffuse light is extra beneficial because of the open crop structure of the Alstroemeria, with which sunlight allows to penetrate deeply into the crop. Because of the warmth-reflective characteristics of the coating the windows can be kept further closed. The relative humidity in the greenhouse is kept on level this way and the stomata will remain opened for a longer period. On the other hand, there is less loss of C02 through the windows, so the C02 absorption will be stimulated even more. This should stimulate assimilation without it costing energy. Those extra assimilates will possibly be utilized in the next period in which assimilation does cost energy (autumn/winter).
The research takes place in an operational greenhouse. One of the two similar greenhouses will be coated with a warmth reflective diffuse coating with high light transmission and a high diffusivity. The climate, crop temperature, stomatal conductance and photosynthesis will be monitored. The dry weight of the rhizomes will be also measured, as will be the production after the removal of the coating. A month after coating the greenhouse roof, there will be a go/no go moment.
Results
During a vast number of hours in spring, summer and autumn, Alstroemeria utilizes the natural daylight moderate to poorly. Particularly above 200 W/m2 irradiation (= 300 μmol/m2/s in the greenhouse) the light efficiency for the photosynthesis in the upper leafs of the cultivation collapses. This is due to a lower stomatal conductance. This in turn obstructs C02 absorption of the leaf. Controlling the stomatal conductance can thus result in a much higher daylight efficiency. In 2016 a practical test was conducted at H.W. Tesselaar to improve the light efficiency for photosynthesis and growth with a diffuse coating with a high degree of light transmission.
Whether or not to use a coating
Based on this research, it is difficult to draw a conclusion on coating for Alstroemerias. There are many factors involved, such as a year with mild weather, different crop varieties and a difficult comparison with the control group. These factors are discussed in the report.
Summarizing, the results show that diffuse light is positive for Alstroemeria. Weaker cultivars will benefit more from diffuse light to prevent light stress than stronger cultivars. A diffuse coating can also function as an ‘insurance’: During summers with relatively few sunny days, the coating will cost money but will not cost production. During summers with relatively many sunny days, the coating will probably result in more production.
The research has been supported by the Dutch program 'Kas als Energiebron' and is financed by the Dutch Ministry of Economics, LTO Glaskracht Nederland, the cooperation of Alstroemeria-growers, Hermadix Coatings and Royal Brinkman.
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