Evaluation of photosynthetic photon flux in lettuce cultivation at different shading levels

Abstract

Protected cultivation has grown in Brazil. Generally, greenhouses are covered with transparent plastic film and shading screen. The plastic, over time, loses its transparency due to pollution residues, dust and other debris. The loss of transparency reduces lightness, photosynthesis and leads to losses of productivity and product quality. The losses are not always detectable by the farmer. Additionally, internal shading screens are used to reduce heating transmission to the ground. The objective of this study was to evaluate the impact of shading on lettuce crop productivity and to determine the optimum shading to reach the highest productivity. Plots were set up inside and outside the greenhouse, with four shading levels with black screens (0, 35, 50 and 75%). The treatments were converted to real shading from the photosynthetic photon flux measurement. The results of fresh and dry phytomass were treated and analyzed by regression as a function of the real shading. In ambient conditions of photosynthetic photon fluxes around 1000 μmol m-2 s-1, reaching up to 2000 μmol m-2 s-1 at some hours of the day, typical of tropical environment, lettuce may support a shading of up to 50% without risk of productivity reduction; under these conditions, shading between 20 and 35% is beneficial, and can guarantee its maximum productivity in lettuce cultivation. It is recommended that the lettuce producer in protected cultivation monitors the shelf life of the plastic, avoiding that the shading exceeds 50%. In order to compare shading experiments, one should use the incident photon flux (FFI) for the whole crop cycle, indicating the minimum limit value of FFI = 600 mol m-2 cycle-1 for the crispy lettuce at an average temperature close to 21oC.

Lettuce Production under Mini-PV Modules Arranged in Patterned Designs

“…However, when analyzing the SS treatment, the above premise was not met. The results obtained for the CS and FS treatments were consistent with the results published in previous investigations [52][53][54][55] but these do not coincide with the result of the SS treatment. In Figure 12, the blue arrows mark the trend of radiation, and the orange arrows mark the trend of expected production.…”

Growth of Vegetables in an Agroecological Garden-Orchard System: The Role of Spatiotemporal Variations of Microclimatic Conditions and Soil Properties

“…Indeed, since the quantum yield of lettuce is greater and its light-saturated photosynthetic rate lower, a reduction in light will lead to a very rapid decrease in its photosynthetic capacity, which is consistent with the lower biomass observed on the B1 beds from 21 to 49 days after planting in our study. Cometti et al [93] have recently found a rapid reduction in biomass of lettuce when level of shade was above 50%. The photosynthetic activity is modulated by temperature as high temperatures are known to favor both plant respiration and transpiration, leading to lower radiation use efficiency and limited photosynthesis [94].…”

Fenologia e desenvolvimento de Pavonia Malacophylla (Link & Otto) Garcke (malvaceae) condicionada pelo ambiente em área de reserva ecológica em Minas Gerais

“…Estes autores discutem a resposta plástica do azevinho em resposta à luz e mostram que a capacidade fotossintética e a condutância estomática variam pouco de acordo com mudanças na oferta luminosa, mas a área foliar, o tecido foliar e a razão entre raiz/parte aérea variam muito. Cometti et al (2020) As folhas são órgãos que apresentam grande plasticidade fenotípica, portanto, podem variar muitas de suas características quando se desenvolvem em ambientes com diferentes disponibilidades de luz solar (Marques et al, 1999;Klich, 2000; ou água e nutrientes minerais. As plantas que recebem menor iluminação tendem a compensar a iluminação deficiente com folhas maiores, para ampliar a superfície de captação de luz e fixação de carbono, além de ter menor risco de aquecimento ou de transpiração excessiva e consequentemente maximizar a eficiência fotossintética (Bragg & Westoby, 2002;Coelho et al 2018).…”