Feeding plants, feeding people – but what about the planet?

The impact of humans on our planet is something which is (quite rightly) receiving increasingly urgent coverage. But what might not be quite so obvious – amongst a sea of stock photos featuring industrial chimneys and car exhausts – is the contribution of agriculture to these damaging processes.

The Earth’s human population is currently 7.7 billion people and growing – that’s a lot of mouths to feed. Cereal farming in particular is essential to achieve this: an estimated 75% of the human energy demand is fulfilled by cereal starch. But farming – no matter which kind – always comes at some degree of environmental cost. These costs include land-use changes, deforestation, disruption / destruction of habitats, soil erosion, and chemical pollution. Is there any way we can better balance our human needs with these environmental costs?

Brachypodium distachyon being screened for nitrate sensitivity. Image courtesy of Nataliia Kuksa, SLCU.

One area where this trade-off is strongly apparent is the agricultural issue of nitrogen fertilisation. Nitrogen is a key plant nutrient – required by the plant for building DNA and protein – which is usually found in low, growth-limiting quantities in the natural soil environment. As a result, farmers worldwide add nitrogenous fertilisers to their fields to boost plant growth and yield.

But this isn’t always great news for the environment. Nitrogenous fertilisers can cause multiple environmental issues; for example, leaching into watercourses and the subsequent eutrophication (overgrowth of oxygen-depleting algae) which occurs damages aquatic life. Soil microbes (the diversity of which is already altered by the addition of fertilisers) break down nitrogenous fertiliser into several gases (methane, ammonia, and nitrous oxide) which contribute to climate change and agricultural air pollution, many of these gases also being dangerous to human respiratory health. Just producing the fertiliser in the first place has environmental impacts, since it relies on either using waste from animal agriculture (organic fertiliser) or on the very energy-intensive Haber–Bosch process (synthetic fertiliser) – with the latter estimated to account for 1% of the Earth’s total energy consumption.

CINTRIN (The Cambridge-India Network for Translational Research in Nitrogen) is a collaborative project which is looking at the issue of nitrogenous pollution in India. Why India? India has a unique set of circumstances which make it an area where promising progress might be made.

CINTRIN’s Dr Varinderpal Singh goes into the field to talk to farmers in the Punjab about the leaf colour chart. Image courtesy of Dr Varinderpal Singh, PAU.

Whilst India is a technologically literate, fast growing country with a current population of 1.3 billion people, this is contrasted by the stark fact that India suffered famines as recently as the 1970s. Avoiding famine in recent times has therefore required strong government investment in agricultural policy, one of which has been to subsidise fertiliser – the nitrogenous fertiliser, urea, in particular.

Usually, nitrogen fertiliser represents a significant part of an arable farmer’s budget, and thus in countries like the UK agronomists and farmers perform calculations on how to reach the best trade-off between the highest yield for the lowest amount of nitrogen possible. However, subsidisation in India has removed this financial incentive to reduce fertiliser application and over-application is common. This has led to many issues with water and atmospheric pollution, particularly in agricultural regions such as the Punjab in northern India, where the south-westerly prevailing wind concentrates atmospheric pollution against the ‘wall’ of the Himalayan mountain range.

In our article, we explain some of the ways in which CINTRIN has opened a dialogue between farmers, agronomists and scientists to find ways to reduce nitrogenous pollution – without putting farmers at a disadvantage or jeopardising Indian food security.

CINTRIN’s Professor Howard Griffiths (University of Cambridge) and Dr Varinderpal Singh (Punjab Agricultural University) discuss agriculture in India. Image courtesy of Dr Varinderpal Singh, PAU .

One of these includes a tool developed by CINTRIN’s Dr Varinderpal Singh from Punjab Agricultural University, who has developed a type of ‘leaf colour chart’, which enables farmers to use the depth of green colour of their crop leaves as a proxy for how much nitrogen (if any) they should add to their fields, and when to do it.

CINTRIN’s Dr Varinderpal Singh demonstrates the PAU Leaf Colour Chart on wheat. Image courtesy of Dr Varinderpal Singh, PAU .

This approach has led to a 50% reduction in fertiliser application without any loss of yield in trials, a positive effect not only for the environment but also the farmers, who were able to use fertiliser more economically and experienced a reduction in pests (the lush, dark green leaves of over-fertilised plants being rather irresistible to many herbivorous insects!)

Farmers raise their hands in support of using the leaf colour chart. Image courtesy of Dr Varinderpal Singh, PAU .

Meanwhile, other areas of the project are looking at how plant physiology and development responds to nitrogen, with the hope that crops which can use nitrogen more efficiently than current varieties do can be bred in the future. We also hope that other future projects looking for solutions to global challenges will also recognise the value of global inputs – after all, with only one planet to share, we all need to be in this together.

CINTRIN’s Dr Stephanie Smith screens a mapping population of Brachypodium distachyon recombinant inbred lines for nitrate sensitivity. Image courtesy of Nataliia Kuksa, SLCU.

Dr Stephanie Smith

Read the paper: Smith, S, Bandyopadhyay, T. (2019) Opening the dialogue: Research networks between high- and low-income countries further understanding of global agro‐climatic challenges. Plants, People, Planet. doi: 10.1002/ppp3.17