Fertilization provides the various minerals required for plant growth. A nutritional imbalance can modify and limit certain processes essential to crop development, in particular photosynthesis.

Photosynthesis comprises two phases. A photochemical phase which converts light energy into chemical energy in the form of ATP* and reducing potential. And a chemical phase in which the Calvin cycle uses this energy to fix carbon for the creation of organic matter.

The photochemical phase is initiated by the absorption of light by chlorophyll. However, nutritional deficiencies, particularly in N, Fe and Mg, lead to a reduction in chlorophyll concentration, thus reducing photosynthesis.

Cu, Mn, N and P are necessary for the reactions that produce ATP. A phosphorus deficiency will inhibit ATPsynthase activity and thus reduce plant productivity.

Depending on the intensity received and the plant’s stage of development, chlorophyll and ATP requirements change. Appropriate fertilization is therefore essential to avoid limiting photosynthesis.

Mineral requirements impacted by spectral quality

Nutrient uptake by plants can be modified by light, and more specifically by the quality of the light spectrum. Indeed, Pinho et al. 2016 showed that adding far-red to red and blue LEDs increased the uptake of macro-nutrients such as K, Ca and Mg in lettuce. Similarly, Fe and Zn uptake was increased by switching from a light to a darker red.

The red/blue color ratio also influences nutrient uptake. Again on lettuce, Chen et al. 2014 showed that a spectrum with 30% blue and 80% red induced the greatest absorption of the following mineral elements: Ca, Mg, Na, Fe, Mn, Zn and B in lettuce. Pennisi et al. 2019 also found an effect of the red/blue color ratio on mineral absorption, with greater absorption of N, P, K and Mg with a red/blue ratio equal to 3.

These experiments have shown that, at equal intensity, mineral uptake differs according to the spectrum deployed. The quality of the light spectrum can influence mineral nutrition via related physiological processes such as carbohydrate translocation, transpiration and stomatal control or growth (Pennisi et al. 2019; Tramblay et al. 1988).

Appropriate fertilization for a successful crop

Light plays a key role in optimizing and controlling production factors. Total control of the light spectrum, in terms of both quantity and quality, opens up new possibilities for optimizing the absorption of micro- and macro-nutrients. Consequently, depending on the light spectrum, specific fertilizations can be implemented to keep plants free from nutritional disorders.