Grain Drain: Rising CO2 Levels May Require Additional Fertilizers
While the role of nutrient management to help manage and mitigate the impacts of global warming on farming is already relatively well known, recent research suggests that fertilizers may soon have an even more important role to play for supporting human health.
Higher concentrations of atmospheric CO2 have been found to reduce the nutrient content of staple crops including wheat and rice and could make an additional 175 million people zinc deficient and 122 million people protein deficient by 2050, according to a study from the Harvard T.H. Chan School of Public Health published last year.
With plant iron content also affected, a significant amount of the dietary intake of 1.4 billion women and children would also be lost, increasing the risk of anemia and other diseases associated with iron deficiency.
Increasing Nutrient Deficiencies
The study compared 225 foods grown in near current atmospheric CO2 conditions, just above 400 parts per million (ppm), with those grown under 550 ppm concentrations, predicted to be the global level by 2050. The latter had protein, iron, and zinc concentrations between 3% and 17% lower.
Plants are the source of the majority of essential nutrients for humans, providing on average 63% of dietary protein, 81% of iron and 68% of zinc daily requirements. Nutrient deficiencies are already estimated to affect over 2 billion people today, mostly in developing countries. If plant nutrient levels were to decrease these deficiencies would grow.
Researchers predicted that India would be particularly hard hit, with around 50 million people deficient in zinc, 38 million in protein and 502 million women and children vulnerable to iron deficiency-associated diseases. Other countries in South Asia, Southeast Asia, Africa and the Middle East would also be affected.
The Trend Towards Nutrient Dilution
Currently used as a type of fertilizer by some greenhouse growers, CO2 improves growth and yield of plants while offering protection under stressful environments such as drought, heat and high radiation.
CO2 also contributes to an effect known as the “dilution problem”: when yields are increased, the starch content of grains generally increases, while at the same time minerals such as Zinc and Iron and the protein content is diluted.
The potential contribution of higher CO2 levels is part of a general recent tendency of plant nutrient level decline. Starting with the green revolution in the 1950s, along with the use of new high yielding cultivars in recent years, increasing yields have resulted in decreased nutrient and protein levels in grains.
Enhancing Nutrition with Fertilizers
The good news is that enhanced nutrient management can play a key role in increasing nutrient levels in crops.
“Agronomic biofortification through micronutrient fertilization can help to increase plant nutrient levels. It’s considered one of the most promising ways to fight malnutrition and alleviate nutrient deficiencies worldwide, especially for zinc, selenium and iodine,” said Sabanci University’s Dr. Ismail Cakmak, whose research under the HarvestZinc program has shown this method to be particularly effective for increasing the concentration of zinc in grains.
Crop protein content levels can also be increased by optimizing nitrogen fertilizer applications. By following 4R nutrient management techniques (using the right source, at the right rate, at the right time, in the right place) farmers can ensure crops get enough nitrogen late in the growing season to increase protein levels after their yield has been maximized.
Although carefully managed fertilization can help counteract some of the possible effects of higher CO2 on plant nutrient levels, the research is also a timely reminder of the need to grow and consume a diverse mix of nutrient-rich crops including pulses, fruits and vegetables.
New Nutrient Opportunities
While there are still some questions over how much of an impact rising CO2 levels will actually have in real world growing conditions (other research suggests that any effects could be offset by rising temperatures decreasing crop yields and therefore concentrating nutrients) the study helps to highlight one of the many potential ways global warming may affect plants.
Amid other research that suggests rising CO2 levels might have additional negative effects on plants – a recent study asserted that thicker leaves would decrease plants’ ability to sequester atmospheric carbon, while another predicted that plants’ water use would decrease resulting in increased soil moisture levels and runoff – it seems there could soon be further need for innovative new fertilizer products, formulations and management techniques.