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 round 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?
In the 1950s, an American scientist named Norman Borlaug working in Mexico created "semi-dwarf" varieties of disease resistant-wheat. By reducing the stalk height by 20%, the plants were far less likely to fall over – an issue known as "lodging" – which reduced their productivity and made diseases more likely to take hold, as well as making mechanical harvesting far less effective.
"An additional benefit of the discovery of those dwarfing genes was that rather than putting the energy into growing a longer stalk, the plant put it into the spike [the ear, where the wheat grains grow]," McGrath continues. "The smaller plant pumps carbohydrates into the grain instead, increasing the amount of grain per plant."
It did this by favouring an enlarged wheat grain endosperm, which the seed uses to feed the growing plant embryo much like an egg yolk feeds a growing chick. This is packed with carbohydrate in the form of starch – the main component of flour.
Producing bigger and more plentiful grains was a welcome improvement at a time when populations in developing countries were rapidly expanding and famine was a threat. However, an unforeseen side effect was that while the wheat produced more grain per plant, nutrient levels did not increase in the same way.
"What we end up with is a scenario where, while the nutrients remain at the same level in a single wheat kernel, the starch is up two or three-fold. This means that once the wheat is processed into flour you get a dilution effect. The ratio of carbohydrates to nutrients is down," says McGrath.
And while carbohydrates are crucial for human health – they provide the energy that keeps us moving and functioning day to day – we also need our diet to provide protein, minerals and vitamins which are critical for growth and biochemical processes in the body. Selenium, for example, is needed in processes that make DNA, zinc helps the body's immune system to work properly, while magnesium maintains nerve, muscle and heart function, and helps bones remain strong.
While the Green Revolution helped to tackle world hunger, today we find ourselves with a global food system that in some cases has been designed to deliver calories and cosmetic perfection but not necessarily nutrition. This is contributing to a phenomenon called hidden hunger, where people feel sated but may not be healthy, as their food is calorie-rich but nutrient-poor. It might initially sound counter-intuitive but obese individuals can be nutrient-deficient. So, can the nutritional quality of our food be restored?
A teaspoon of soil contains more microbes than there are people on the planet, and perhaps as many as 10,000 individual
species
While some scientists feel the fall in nutrient levels in our food over the decades is too small to be significant compared to the increase in food availability provided by improved yields, the health of our soils is still thought to have an important relationship to the nutritional quality of our food. A trial in the US has been examining vegetables grown under different farming techniques to better understand exactly what this link is.
"The vegetable systems trial started in 2016 and is a side-by-side comparison of crops grown in soils managed with intensive practices and regenerative organic tillage practices," says soil scientist Gladis Zinati of the Rodale Institute in Pennsylvania.
The goal of the study, which is designed to run indefinitely, is to link farming practices and soil health to crop nutrient density (or the amount of nutrients a food contains relative to the amount of calories) and human health.
Zinati's research suggests that the more fungi and microbes that are active the soil, the better equipped it is to get nutrients into plants and our diet. In other words, soil teeming with fungi and bacteria is better able to break down nutrients into a form that can be more easily gobbled up by the crops.
The initial findings are due to be peer-reviewed with a view to publishing in the coming year.
Soil is made of four elements in varying proportions: minerals in the form of rock particles, organic matter (plant, fungal and animal materials including microbes and microscopic worms, either dead or alive), air and water. But the important thing is how these elements interact.
Here is the genetically modified GM
A teaspoon of soil contains more microbes than there are people on the planet – we're talking billions, and as many as 10,000 individual species. Intertwined with all that mind-boggling life is a network of fungal filaments called mycorrhiza, a symbiotic relationship with plants and microbes that act as extensions to their roots. There is a constant dance of nutrient pass-the-parcel from soil to plant, powered by complex biochemical pathways, fungal superhighways and exotically named root exudates, which is basically root snot that stimulates or represses a wide array of biological activity in the soil.
The influence of mycorrhizae is such that it has been commercially harnessed to improve crop productivity. GroundworkBioAg in Israel has produced a soil inoculant based on particularly vigorous strains of mycorrhizal fungi, sourced from the Israeli desert.
These specialised soil fungi effectively extend the plant root system with mycelium – a web of long microscopic filaments called hyphae. They work in a symbiotic relationship with the plant, releasing nutrients from deep in the soil, in a form that the plant can absorb.
When this commercially produced powder is used to coat roots or seeds, the resulting impact on crop yield has some farmers embracing these remarkable fungi over artificial agrochemicals.
US farmer Cory Atley farms 8,000 acres (32 sq km) of maize and soybeans in Ohio and has been trialling the use of the inoculants. As well as seeing a boost in crop growth through the release of nutrients from the soil, he has found he is spending less on chemical inputs.
"What we are really trying to focus on is soil health, so once you get your soil health aspect of it down, it will translate into plant health. We're still using synthetic fertiliser but we're using less and less, about 25% less. What we're trying to do is break apart more of what is already in our soil, instead of constantly adding more to the soil."
It's not only highly adapted fungi that are improving food productivity and the movement of nutrients – plants that have evolved to survive harsh conditions are also proving useful.
In Kenya, livestock are a key part of the economy, contributing around 12% of the national GDP. In the smallholder mixed crop-livestock system, livestock play a significant role in food and nutritional security, income generation and as a source of manure for soil fertility in crop production.
Dairy farming is especially important in Kenya, and it is one of the leading dairy producers on the continent. However, poor quality feeds and seasonal scarcity limit productivity, with the average yield at about eight litres (1.8 gallons) per cow each day compared with 25-50 litres (5.5-11 gallons) per cow each day elsewhere in the world. Donald Njarui of the Kenya Agricultural and Livestock Research Organisation (Kalro) has been researching ways to improve the situation, through the introduction of improved forages.
"Most smallholder dairy farmers in the country have just two to five cows," says Njarui. "So any increase in productivity can have a profound impact on their lives. Over 90% of smallholder dairy farmers rely on Napier grass, which is used in a 'cut-and-carry' feeding system, where the grass is harvested and delivered to the animals. However, Napier has become susceptible to pests and diseases, which reduce biomass yield significantly. There was a need to look for other viable and sustainable options that farmers can depend on for their dairy cattle."
And that search started overseas. A type of grass called Brachiaria has been commercialised in South America, Australia and Asia where it has transformed the beef and dairy industry in those regions. Surprisingly, Brachiaria grass originates from Africa, but it has not been exploited there for livestock feed in the same way – until now.
The impact has been significant. Milk yields rose, the health of the cows improved, crude protein levels are up compared to Napier grass, says Njarui, and it is less fibrous and more digestible, meaning animals feeding on it produce less greenhouse gases. "Due to its massive root system, it also has the ability to sequester more carbon into the soil than local pastures."
The super-grass's success is simple – it has adapted to drought and low fertility acidic soils by creating a large, extensive root system, so has the ability to draw more nutrients from deep in the soil.
Whether it is natural or human selection, farming techniques or the weather, the nutritional content of our food is influenced by many factors. Ensuring that we get the best version of the foods we grow requires an in-depth understanding of the network of nutrients that flows around us. Can we incentivise farmers to grow better quality food over higher yields?
What we would need is a food production system which monitors nutrition in food and makes it universally comparable, and a commercial model that values nutrition above everything else, concludes McGrath. How that could be achieved remains to be seen.
"Farmers need to be paid for effective nutrient yield, not just mass of produce. Right now, the model of being paid per tonne of grain doesn't stack up from a human health perspective," says McGrath.
There are many moving parts in the links between nutrition and farming, and much that is not yet fully understood. Simply put, more research is needed, but with more than two billion people globally affected by micronutrient deficiencies, so much good could come from following the trail of nutrients.
