An innovative project in Luxembourg is demonstrating how smart cropping methods can increase the carbon sequestration capacity of soils even in conditions of drought. Better soil health is achieved thanks to the introduction of low-emission cropping practices, including cover crops and undersowing.

ADAPT, a nationally funded project which started in 2022 and is coordinated by the Luxembourg Institute of Science and Technology, is developing a smart crop management system. Project coordinator Kate Buckeridge explains: “Climate policies encourage farmers to lower greenhouse gas emissions. At the same time, better soil health can make crops more resilient when faced with climate change. So we set up this project to support farmers in protecting soil carbon and plan for future climate scenarios while maintaining the productivity of their farms.”

The ADAPT project focuses on a practical combination of cover crops, undersown crops, minimal tillage and reduced nitrogen fertilisers. Field trials over three years have demonstrated that the project’s ‘smart cropping’ approach can almost double microbial biomass carbon, without increasing nitrous oxide (N2O) emissions. Yield and yield quality are still being measured, but there seems to be no significant reduction in yield.

Kate explains the efficiency of their approach: “For example, the undersowing of perennial crops, that is to say growing a secondary crop in between the rows of the main crop, provides ground cover and prevents erosion. This method improves soil carbon content and can increase the yield of the primary crop by storing water and making it available to the crop for a longer period during droughts.” One of the challenges, however, of using legumes as cover or undersown crops is that they release nitrogen continuously, not just when the main crop needs it. Kate explains, “Within the ADAPT project, we are finding the right balance of methods to increase carbon sequestration while keeping emissions as low as possible.”

Two arable farmers, one in the north and one in the south of Luxembourg, were involved in the ADAPT field trials. Focussing on a three-year crop rotation of maize, wheat and barley, the project simulated periods of drought by using passive rainshelters that diverted rainfall, reducing it by 65% over three months during springtime. The ADAPT approach was compared with conventional cropping methods in similar plots on the same farms. Researchers from the project measured soil temperature and moisture and collected soil samples to analyse microbial and earthworm abundance and microbial diversity.

Kate explains, “It was important for us to work together with the farmers to understand the barriers to implementing such practices.” For example, on one of the farms, the cover crop did not cover the ground sufficiently after the first year to prevent weeds, so minimal tillage was implemented after the first crop (maize), and the cover crop was then replanted. On the other farm, planting the main crop (barley) was delayed because it was difficult to source the machinery needed to sow barley into the cover crop. Kate continues, “Now that some of the big challenges are known, such as weed competition and timing of operations, we can test these factors in experimental trials and then bring the best combination back to the farmer in future collaborations”.

A final aspect of the ADAPT approach is to use a process-based computer simulation to model the exchange of nutrients and carbon in the plant-soil system in the current and future climate.