Growing grasses amongst blueberry (Vaccinium spp) bushes boosts the berries’ antioxidant content by correcting iron deficiency – a common problem in the plant – reports a study published in the journal Frontiers in Plant Science.
Also improving the fruit yield, the grasses produce a similar effect to that achieved with a chemical iron fertiliser. However, the study’s authors suggest, the grass intercropping offers a safer, more environmentally friendly way to grow the commercially valuable crop.
All plants need iron to make important molecules such as chlorophyll, which gives them oxygen and produces their green leaves. Without it, they become sickly and grow poorly.
Iron also facilitates enzymes needed to produce polyphenols, antioxidant compounds with numerous health benefits that have earned blueberries their “superfood” status.
But the species struggles to use the insoluble iron commonly present in soil.
“Most plants get enough iron by secreting chemicals that make it more soluble,” says senior author Jose Covarrubias, from the University of Chile.
“These iron ‘chelators’ can be released directly from the roots, or from microbes that grow among them, and allow the iron to be absorbed.”
Blueberries evolved in unusually acidic, wet conditions that broke the iron down for them, so they haven’t adapted to use iron from the earth’s predominately dry, alkaline soil.
Two ways to correct iron deficiency in blueberries are to acidify the soil or add synthetic iron chelators. However, these are not ideal, says Covarrubias.
Soil acidification with sulfur is slow and can hinder root growth, while directly applying acids can be toxic to farmers and soil microbes.
The other common method of using synthetic chelators in the form of fertilisers is costly, and the potentially toxic chemicals could seep into the water table.
The researchers noted that grasses are well-adapted to poor soils and their roots can provide fruiting plants with a natural source of iron chelators – as demonstrated previously through improved growth and yield of olives, grapes, and citrus trees.
Covarrubias and colleagues tested the effects of five different conditions on blueberries in an orchard with alkaline soil: a commonly used synthetic iron chelator, intercropping with common meadow grass, or red fescue grass (Festuca rubra), applying cow’s blood, and leaving a patch untreated.
Compared to cow’s blood and no treatment, the grasses and synthetic iron chelator improved the berries’ weight, and volume of antioxidant compounds. Red Fescue grass also improved yield. Greener leaf colour suggested that increased iron uptake was responsible.