Partial peat replacement by biochar as a potential strategy to increase plant growth, nutrient sink and circular economy

The use of peat in traditional agricultural systems and nursery enterprises is an environmental concern. Since the high CO₂ and greenhouse gas emission due to peat excavation contributes considerably to climate change and global warming it is key to find new valuable resources in the field of carbon based materials production and application. This approach not only contributes to the concept of circular economy and the reduction of contaminants and waste, such as excessive nitrogen (N) fertilizers, but is also beneficial with respect to nutrient recovery and use efficiency. In this work we partially replaced peat with different amounts of biochar obtained from vineyard pruning as plant growing substrates while implementing N fertirrigation. We studied the effect on the growth, different content of N forms and other nutrient dynamics impact of lettuce plants grown under greenhouse and semi-hydroponics conditions. Substrate mixtures contained 30% of vermiculite and 70% of different biochar:peat treatments as follows: 0:70 (B0), 15:55 (B15), 30:40 (B30), 50:20 (B50), and 70:0 (B70). Higher biochar treatments increased pH and electrical conductivity of the substrate, negatively affecting plant growth and germination (especially in B70). The substitution of 30% peat by biochar (B30) delayed seed germination but improved plant growth and N use efficiency. This is related with a higher nitrate (NO₃^‒) retention capacity in the substrate, leading to higher contents of organic N and NO₃^‒ in the plant shoot. The treatment B30 also increased the water holding capacity of the substrate, which may enhance soil moisture characteristics and pore size distribution, maximizing water availability to plants. Our study demonstrates that the use of biochar can reduce the consumption of peat and excessive N fertilizers, while promoting a more sustainable farming with positive impact on both the plant growth and the environment.

Acknowledgement: This research was funded by European Union’s Horizon 2020 research and innovation programme un-der the Marie Skłodowska-Curie grant agreement No 895613 and EIT Food program (Black to the Future Project, EIT-21217). This EIT Food activity has received funding from the European Institute of Innovation and Technology (EIT), a body of the European Union, under Horizon Europe, the EU Framework Programme for Research and Innovation. A.F. Garcia-Rodriguez acknowledges the Spanish National Research Council for providing JAE Intro-ICU grant.