Cover crops reflect light - can it mitigate climate change?

Video: What is albedo?

Variation throughout the day and year

Many of these factors vary over time. Furthermore, not all solar radiation reaches the earth's surface. A significant portion is reflected by clouds or absorbed in the atmosphere. In winter and in the morning and evening hours, when the sun is lower above the horizon, there is less radiation reaching the earth. Conversely, in summer and in the middle of the day. It is therefore important to take variation in irradiance into account when assessing the albedo effect of crops.

Crops usually increase the albedo effect

Typically, there is a tendency for higher albedo for plant-covered soil than for bare soil, but you should be careful with generalisations due to the many factors that affect reflectance.

As mentioned, snow is important. Snow covers a bare soil surface more easily than a vegetated one, but plant growth also plays a role. Tall, leafy species stick up through the snow and reduce albedo, while low-growing species are more easily covered by snow, which enhances albedo. Since not much snow falls in Denmark and most of it falls during periods of low radiation, snow is probably of limited importance under Danish conditions.

Quantification is complex

There have been several attempts to quantify the albedo effect of cover crops. Effects of between 5 and 46 g CO2e/m²/year have been estimated in the research literature. The different estimates are difficult to compare due to the different assumptions, measurements and cultivation conditions of the studies and the high uncertainty associated with converting albedo effects to CO2 equivalents. Finally, the estimates are strongly influenced by regional climate conditions and therefore cannot easily be used to assess the potential in a Danish context.

Technically, the quantification of changes in albedo can be performed by combining ground-based radiometer measurements with satellite data. Models based on satellite data exist for Denmark, but there is a lack of data based on ground measurements.

Video: What is the climate effect of albedo?

Is there room for more cover crops?

Winter-sown crops limit the possibility of integrating catch crops into crop rotations. In Denmark, it is estimated that 25 per cent of the total crop rotation area was planted with catch crops in 2020, and the potential is estimated to be at most a third of the rotation area. In addition, winter cereals obviously also have a higher albedo than bare soil, so the difference between winter cereals and cover crops is significantly smaller. This is also investigated in the project.

Report: Reflect the light, by Tine Engedal (pdf, 7 pages)