It looks like a carrot, it tastes like a carrot, but is it as good for us as it once was?
The nutritional values of some popular vegetables, from asparagus to spinach, have dropped significantly since 1950. A 2004 US study found important nutrients in some garden crops are up to 38% lower than there were at the middle of the 20th Century. On average, across the 43 vegetables analysed, calcium content declined 16%, iron by 15% and phosphorus by 9%. The vitamins riboflavin and ascorbic acid both dropped significantly, while there were slight declines in protein levels. Similar decreases have been observed in the nutrients present in wheat. What's happening?
Prompted by food shortages after World War Two, scientists developed new high-yield varieties of crops and breeds of livestock, alongside synthetic fertilisers, pesticides and herbicides, to boost food production. Coupled with improvements in irrigation and the advent of affordable tractors, crop productivity increased dramatically. The average global cereal yield rose 175% between 1961 and 2014, with wheat, for example, rising from an average yield of 1.1 tonnes per hectare to 3.4 tonnes per hectare in around the same timeframe.
While yields went up, nutrient levels in some crops declined, bringing intensive farming techniques under scrutiny. Could it be, as some have claimed, the result of the increased use of artificial pesticides, fertilisers and other chemicals disrupting the fine balance of soil life, the health of crop plants, and therefore affecting the quality of the food we eat?
A 170-year study into wheat grown using different farming techniques in the UK suggests there is more going on.
"The Broadbalk experiment is one of the oldest continuous agronomic experiments in the world. Started in 1843, it has been comparing the effect of inorganic [artificial] fertilisers and organic manures on winter wheat. It has specifically examined the levels of iron and zinc in wheat grown under different farming methods," explains Steve McGrath, a professor in soil and plant science at Rothamsted Research in the UK.
"First, our findings show that it isn't a lack of micronutrients in the soil that is driving the lower nutrients in the crop. Those that are bioavailable, that is, in a form that the plant can absorb, don't change with intensive farming methods."
So, if the soil is as good as it was, what else is going on? Have the plants themselves changed?