Linking Soil Health to the Nutrional Quality of Fruit.

Sir Albert Howard argued that the “nitrogen cycle between soil and crop” was key to healthy plants and people. Recent evidence suggests that organic soil management improves nutritional attributes of fruit, such as phytochemical concentrations and antioxidant capacity. In several studies, we found positive links between soil fertility management and these crop quality parameters. These studies included a field comparison of organic and conventional apples (Malus x domestica) in Washington State, matched pairs of commercial organic and conventional strawberry (Fragaria x ananassa) fields in California, and greenhouse studies of tomato (Solanum lycopersicum) plants grown with organic or inorganic fertilizers and exposed to herbivory by green peach aphids (Myzus persicae). Organic apple and strawberry fruits had 5-20% higher phytochemical concentrations and antioxidant capacity than conventional fruits, and these were linked to indicators of soil biological activity. Similar increases in phytochemcials and antioxidant capacity were found in tomato fruit that were grown using organic fertilizers, but sometimes these differences were cultivar dependent. Soluble solids and dry matter were usually higher in organic fruits, but this also varied by cultivar. Aphid populations were lower on organically grown tomatoes, while both organic fertility management and herbivory increased phenolics concentration in fruit. These differences suggest that improved nitrogen cycling may enhance defense compounds in tomatoes grown with organic fertilizers, whereas herbivory may enhance them in tomatoes grown with inorganic fertilizers. Our current genomic analysis may explain these functional differences. The implications of this analysis will be discussed in relation to crop management practices.