Effects of growing media and fertilization rates on the organic production of baby leafy vegetables

The growing consumer demand for fresh and pesticide-free food is driving the development of controlled-environment agriculture worldwide.
In organic cultivation systems, the physicochemical and biological properties of growing media and fertilization management are the main determinants of the crop performance and product quality.
The objectives of this study were to evaluate the impact of five rates of nitrogen organic fertilization (0, 50, 100 (standard with 14 g N m^‑2), 150, 200%) on six species of baby leafy vegetables used as salad microgreens and grown in three growing media amended or not with biostimulants (PG, Pro-Mix^® pg ORGANIK as peat-based control; MP, Pro-Mix^® MP Mychorrhizae ORGANIK; MP+, Pro-Mix^® MP Mychorrhizae ORGANIK with seaweed and humates). The potential benefit of reusing these growing media for a second growth cycle was also evaluated.
The experimental design used was a randomized complete block with 4 replicates.
Our results showed that the most performing growing medium is species dependent; MP+ being the most promising for shiso, basil and lettuce, while MP increased the foliar NO₃ concentration of all species (except for basil) compared with PG. Adding only mycorrhizae to the growing medium did not improve foliar P content, except for spinach and lettuce, while MP+ increased its concentration for chicory, shiso, basil, and lettuce.
Regardless of the growing media, the shoot biomass was greater under the highest fertilization rate of 200% for spinach and Swiss chard, while the control treatment gave the highest shoot biomass for chicory, shiso, basil and lettuce; the 150% treatment did not result in a better yield and the 200% had a negative impact.
For all species, the 0 and 50% fertilization rates resulted in a lower shoot biomass and plant height compared with the control.
On the other hand, plant photosynthetic performance was generally higher under 150 or 200% fertilization rates, while lower values were observed under 0%. Increasing the fertilization rate generally enhanced the mineral leaf content, except for shiso and basil.
Increasing N levels, however, increased the leaf nitrate content of all species, except for basil; highest levels of nitrate were observed for chicory and lettuce exposed to 150 and 150% N. The use of the same growing media for a second growth cycle increased by 118 to 204% shoot biomass of spinach, Swiss chard and chicory compared with the first growth cycle, and the 200 and 150% fertilization rates had a residual beneficial effect on shoot biomass of spinach and Swiss chard.
So, depending of the plant species and their leaf nitrate content, the fertilization rate should be adjusted in order to fulfil plant nutrient requirements, without providing nutrient excess and environmental burdens.

IV All Africa Horticultural Congress – AAHC2021: Transformative Innovations in Horticulture

D.M. Dembele, T.T.A. Nguyen, A. Bregard, R. Naasz, F. Jobin-Lawler, C. Boivin, M. Dorais

growing media, fertilization rates, greens, leafy vegetables, productivity, nutrients

https://doi.org/10.17660/ActaHortic.2022.1348.20