N and P use efficiencies of basil cultivated in organically fertilized growing media

Sustainable production in soilless cultivation systems may be achieved by using recycled organic materials as constituents of growing media (GM) and as organic fertilizers. Synchronizing nutrient releases from organic fertilizer mineralization with plant needs in containerized production is difficult to manage for greenhouse growers. This is further amplified by the diversification of GM constituents, driving microbial activities. We aimed to evaluate how the plant can adapt its nutrition to different organic fertilization strategies and ensure its growth depending on the GM and organic fertilizer types. Ocimum basilicum L. was grown for 60 days in a greenhouse in pots filled with three different GM: 100% peat (Peat); 70% peat and 30% coir fiber (GM1); and 50% coir pith, 25% composted bark, 25% wood fiber (GM2). Two contrasted organic fertilizers were used (horn and a granular fertilizer), mixed to the GM, localized in the pot, or combined with Bacillus sp. inoculation as plant growth-promoting rhizobacteria (PGPR). Standard mineral fertilization mixed to the GM was also used as a control treatment. We investigated basil growth (height, biomass, leaf area, chlorophyll and flavonol contents) as well as nitrogen (N) and phosphorus (P) use efficiencies, from their uptake by the roots to their allocation to the plant organs. Basil performances were mainly affected by the GM type. Peat provided optimal conditions for plant development. In GM1, basil maximized the utilization of available N and P taken up from the GM and reached the highest biomass production. Basil performances were especially low when it was grown on GM2 because of a strong competition for N between microbes and the roots. The fertilizer type, its localization and PGPR inoculation did not affect basil growth or nutrition in peat; these treatments had only little effect on basil grown on GM1 and GM2, and affected its performances differently depending on the GM type. This study provides evidence that fertilization must be thoughtfully managed depending on the GM in organically fertilized systems.