How peas and beans can shape soil health and the next harvest
A new study published in Plant and Soil has found that the remains of pea and bean crops left in fields after harvest can affect soil health and how well the next crop grows.
Researchers from The James Hutton Institute and the Universidade Católica Portuguesa in Porto studied different varieties of peas and field beans to see how their leftover stems, leaves and roots influenced the soil and a subsequent barley crop. They found that the effects depended on both the type of plant material and the amount returned to the soil.
The Hutton’s Professor Pietro Iannetta, a co-author on the study, said the findings reinforce the value of returning crop residues to the soil, but added, “Understanding genuinely regenerative cropping systems demands more detail regarding the chemical nature of crop residues, how much is returned, when it is returned and how it interacts with soil biology and the crop that follows.”
“Understanding genuinely regenerative cropping systems demands more detail regarding the chemical nature of crop residues, how much is returned, when it is returned and how it interacts with soil biology and the crop that follows.”
Professor Pietro Iannetta, The James Hutton Institute
Professor Iannetta is especially interested in pulse crop residues that provide low and high levels of certain natural plant compounds known as phenolics. These can play a protective ecological and physiological role for both soil and gut health. He explained, “Such phytochemicals – the naturally occurring chemicals present in, or extracted from, plants – are being bred out of the most cultivated pulse crop varieties for mainly monogastric (farmed chicken and pig feed) markets. Consequently, we should work to understand the impacts and trade-offs of this major influence.”
The findings highlight the need to view crops as part of interconnected biochemical systems rather than in isolation, taking into account their broader role within agricultural ecosystems.
Legume crops such as peas and beans are already valued for adding naturally acquired nitrogen to the soil, reducing the need for manufactured fertilisers. This study shows that phytochemical diversity may also influenced post-harvest toil processes, with crop residues affecting key biological and nutrient cycles.
The researchers found that moderate amounts of residues from some pea and bean varieties boosted soil microbial activity, improved nitrogen availability and helped barley growth comparable to that achieved with synthetic nitrogen fertiliser.
However, very large amounts of residue had the opposite effect, reducing microbial activity, lowering nitrogen availability and slowing barley growth
The study suggests that different pulse crop varieties leave behind different soil legacies, meaning some may benefit the following crop more than others. This could give plant breeders with a new selection criterion, alongside yield and disease resistance, based on a variety’s contribution to soil health and future crop performance.
One important finding was that residues rich in phenolics appeared to change the way nitrogen is used below ground, making the nitrogen available to plants over a longer period.
The researchers note that the highest residue levels tested were far greater than those typical found on farms and were included to better understand soil processes. Lower residue levels are, therefore, likely to be more relevant to practical farming systems.
Further field studies will be needed to determine how these effects develop over several growing seasons, as the study examined only the first eight weeks of barley growth under controlled conditions. The team also wants to explore how crop residues affect greenhouse gas emissions, soil carbon storage and long-term soil health.
Overall, the findings highlight the importance of crop phytochemical diversity as part of a true holistic crop rotation, showing that crop choice can influence agroecosystem functions and the performance of the farming system as a whole.