Researchers of the Research Group Rural Rural Engineering ’of the University of Almería have published an article in the prestigious magazine Agronomy in which it establishes the influence of different doses of bleaching of the greenhouse cover on the interior microclimate and on the agronomic behavior of a tomato crop; Presenting directly applicable practical recommendations by farmers.

The bleaching of the cover is carried out in the greenhouses of Almeria for decades to reduce the interior temperature by increasing the reflection of radiation that impacts greenhouses, but has the negative side effect that less usable radiation reaches the crop to perform photosynthesis, and production is not achieved optimal.

This study by researchers from the UAL delve into the proper management of this low-cost climate control technique to increase crop production. The study concludes the advisability of doubling the usual dose in the application of bleaching in the autumn-winter crop cycle and halving the spring-summer crop, since these changes provide larger fruits. Applying the necessary doses at each time of the year, a passive technique without energy consumption, will help at no additional cost to increase the productivity of farms.

The test was carried out on two consecutive tomato growing cycles. During the course of the first growing cycle (autumn-winter), the effect of different bleaching doses selected based on the range of concentrations used by farmers in Almería was evaluated. The application method was that used by companies in the sector, where the CaCO3 solution is applied with a spray nozzle while the operator moved over the surface of the greenhouse roof.

On the other hand, the effect of bleaching on photosynthetic activity, production, morphological parameters of plant growth and the quality of the harvested fruits was analyzed. In addition, the various components of solar radiation were studied, particularly the photosynthetically active spectrum (PAR), air and soil temperatures, and heat flux in the soil; In this way, an accurate energy balance could be made to evaluate the effect on the greenhouse microclimate. The results showed to what extent the increase in the bleaching dose reduces the transmissibility of the cover, decreasing the extreme maximum temperatures at the beginning of the autumn-winter cycle and reducing photosynthetic activity throughout the rest of the year. As a result of the lower levels of photosynthesis caused by the increase in bleaching in the autumn-winter cycle, significant production losses were observed, around 0.8% -1% for each 1% reduction in transmissivity, so it would be advisable to apply the concentration of 0.500 kg L-1 (double the usual) for the start of the autumn-winter crop cycle and wash the cover in mid-September, to avoid production losses.

Regarding the spring-summer crop cycle, the variable dose was not effective comparing it to a constant application (0.250 kg L-1), due to the negative effect of the reduction of photosynthesis, and therefore of production, caused by use higher doses. The plants were more favored throughout their production cycle (increasing productivity), due to the most appropriate conditions in their early stages of development, where less bleaching doses were applied. For this reason, the researchers of the University of Almería They recommend applying doses of 0.125 kg L-1 at the end of spring.

The Research Group is developing low-cost techniques directly applicable by farmers to improve the productivity of greenhouses and reduce costs; based on an increase in the photosynthetic activity of the crops, by reducing the blanching of the cover, the increase in natural ventilation, cover plastics and photoselective double ceilings, improvement of the plant architecture and the use of reflective padding.

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