Carbon content of agricultural soils is currently declining on a global scale. Although this might not be directly recognised as a problem by the average citizen, it has some serious consequences. A decline in carbon in agricultural soils threatens soil fertility and makes soil prone to erosion. This is problematic for the cultivation of food, already today, but especially in the long term.
During a four-year field trial in Finland, LUKE and Soilfood Oy investigated how to decrease soil erodibility in a circular manner. For this, they used organic sludges that are produced as side streams by the pulp and paper industry. These occur in high quantities (in Finland, 420,000 Mg dry matter per year) and are usually incinerated with low net energy recovery. With the idea of integrating these valuable substances into new value chains, the researchers used different organic sludges and studied their effect on cereal yield, soil carbon content and fungal and bacterial composition. The trail included 1) composted sludge, 2) lime-stabilized sludge (both derived from the process water treatment plant at the factory) and 3) fiber sludge, which consists of cellulose fibers that are too short for the mill’s final product.
The field experiment and rainfall simulation study indicated that fiber, composted and lime-stabilised sludge from the pulp and paper industry can be used to mitigate adverse effects of food production on the quality of discharge waters. The amendments demonstrated a potential to reduce soil erosion through soil monoliths over several years. They also increased the pools of microbial-bound carbon and nitrogen in soil. A particularly interesting observation was the increased proportion of Sebacinales fungi, which in organic farming are used as indicators of improved soil quality. However, on cereal yield and grain quality, the soil amendments had only minor effects.
The finding that the use of pulp and paper mill sludges decreases soil erodibility is important for two reasons. Firstly, because it helps us better understand the composition of agricultural land and the effects of adding organic by-products to the soil. And secondly, because it is a step in the right direction for practical use of valuable organic side streams. This is essential for a circular economy, but also contributes to CIRCLES’ goal of delivering new and healthier food applications through microbiome research.
Rasa K, Pennanen T, Peltoniemi K, et al. Pulp and paper mill sludges decrease soil erodibility. J. Environ. Qual. 2021;50:172–184. https://doi.org/10.1002/jeq2.20170
Written by Hague Corporate Affairs