Chemical fertiliser use could be reduced if farmers deployed nature-based farming techniques, according to a major scientific study.
Analysis of 30 long running farm trials has shown that the high crop yields usually obtained using artificial fertilisers can instead be achieved through more environmentally friendly practices.
The report, by Rothamsted, is the first time a major study has compared different farm practices that intentionally work with nature to boost yields and explored how they interact with fertiliser use and tillage practices.
Published in the journal Nature Sustainability, it shows that low levels of fertiliser can produce high crop yields if supplemented by practices that support farmland ecosystems.
This includes growing a greater range of crops, growing plants such as beans or clover that enhance soil fertility, and adding organic matter in the form of manure, compost, or cuttings.
In contrast, using these practices along with high levels of chemical fertiliser didn’t generally increase yields further, and the highest experimental yields came when using a combination of these ‘ecological intensification’ practices with some additional nitrogen.
Researchers say these findings show that adopting some, or all, of these approaches could help reduce and rebalance worldwide fertiliser use, a global imperative given spiralling prices caused by the war in Ukraine.
Dr Chloe MacLaren, of Rothamsted Research, said: “Reducing reliance on chemical fertilisers would help to buffer farmers and consumers against economic shocks, such as the current spike in fertiliser costs and consequent increase in food prices.
“Widespread uptake of these practices could also contribute to a more equitable global distribution of fertiliser," she explained.
"Currently, average nitrogen fertiliser rates in Africa are a small fraction of those in Europe, with smallholders in particular using much less than their fair share.
“If fertiliser use is reduced where it is currently high, then fertiliser use could be increased where it is currently low - addressing food security issues without exceeding planetary boundaries.”
Ecological intensification is where natural, environmentally benign processes that can benefit farming, such as those that enhance soil fertility or suppress weeds and disease, are actively encouraged by farmers.
“Ecological intensification could help return agriculture into a ‘safe operating space’ for humanity,” said Dr MacLaren. “Our results demonstrate that it could play an important role in the development of future sustainable farming systems.”
Looking at their results, researchers in the report concluded these practices work in different ways to increase yields.
Growing legumes such as beans and clover add nitrogen to soil, which is important when fertiliser levels are low, whereas growing a greater range of crops over the year helps suppress weeds and diseases, which appeared to be increasingly important when higher rates of fertilisers were used.
Organic matter improves soil structure while also adding nitrogen, and manure was found to have a greater impact on yield than adding plant-based composts or cuttings, or leaving the remains of crops in place after harvesting.
According to Dr MacLaren, data from long-term experiments was key to demonstrating that the benefits of ecological intensification hold over long timescales, and across a wide range of contexts.
“Short-term experiments can produce spurious results if they take place in unusually good or bad years,” she said.
The team looked at farm experiments that have been running for longer than nine years from across Europe and Africa – totalling 30 separate experiments and data from over 25,000 harvests. The crops tested were wheat, maize, oats, barley, sugar beet or potatoes.
Each trial looked at least one of the three types of nature-friendly farming approach. Across the full dataset the researchers could assess the effect of different ecological intensification practices alongside different levels of nitrogen fertilisers and ploughing.
This meant the study could explore how multiple ecological intensification practices interact with each other and with nitrogen fertiliser inputs in their effects on yield, which had not been studied before.
The results also showed that a reduction in how much fields were ploughed did not strongly affect yields, although there are other economic and environmental factors that mean farmers may want to reduce their tillage efforts, says Dr MacLaren.
“Future assessments of ecological intensification should include a wider analysis of all social, economic and environmental factors, such as nutritional value or farm profitability.
"There are undoubtably benefits beyond just yield, such as reducing costs, reducing pollution, or providing other valuable farm products."
She added: “Conversely, socioeconomic factors can also limit the adoption of such practices by farmers. These factors can include a lack of markets for these diverse products and limited access to necessary resources including land, seed, and manure.
"Upscaling these practices will require policymakers and society to create a more conducive socioeconomic context.”
