Health-Promoting Phytochemicals in Organically Grown Pac-Choi and Tomato with Different Fertility Levels in Open Field and High Tunnels

The effect of contrasting growing and management conditions and fertility levels on the health-promoting qualities of pac-choi (Brassica rapa L. ‘Mei Qing’) and tomato (Solanum lycopersicum L. ‘Bush Celebrity’) was studied in a 2-year field trial.  Crops were grown under organic and conventional production practices in high tunnel and open field at various levels of fertility. In both pac-choi and tomato, crops grown in open field had higher total phenolic content and antioxidant capacity than their counterparts grown in high tunnel. However, spring pac-choi appeared to be more responsive to open field environment than the fall crop. In both spring and fall pac-choi crops, the levels of chlorogenic acid and caffeic acid were significantly higher in crops grown in open field than those gown in high tunnel under both organic and conventional environments. Similar results with regard to chlorogenic acid and p-coumaric acid were observed in ripened tomato fruits. However, more striking response was in rutin content in tomato fruits in that fruits from open-field had nearly twice the amount of rutin as those from the high tunnel.  The response of phytochemical accumulation in open field appears to be related to the increased light that these plants receive relative to those in tunnels. However, the biomass accumulation and the yield were significantly lower in crops grown in open field  than in high tunnels. With regard to the comparison between organic and conventional, the response of total phenolic content and individual phenoilc compounds in both pac-choi and tomato was variable and a clear trend was not observed. With regard to fertility, control plants receiving no fertilization under conventional management produced higher content of both total phenolics  and of several individual phenolic compounds in both pac-choi and tomato. Thus, increasing fertility tended to decrease the phenolic content.  For example, the rutin content in tomato fruits decreased sharply with increasing fertility and the highest levels were found in control plots receiving no fertilization under conventional management practices. However, the results with organic management did not follow a similar trend, perhaps due to the residual and slow release of nutrients from the organic sources in these plots. The results show that producing pac-choi and tomato crops in open-field (high light) with low fertility (nitrogen) significantly enhances their quality with regard to the heath-promoting phytochemicals.