Short-term improvement of soil biological activity in biochar-amended organic greenhouse tomato crops

M. Dorais, F. Gagnon, S. Laurin-Lanctôt, M. Thériault, C. Ménard, S. Pepin
Several studies have shown that adding biochar as soil amendment to agricultural land can increase the sustainability and productivity of cropping systems by sequestrating C from the atmosphere into the soil, by minimizing the emission of greenhouse gases (GHG), by improving soil properties and soil fertility via its effects on porosity, particle aggregation, soil structure, water and nutrients retention, and by improving microbial activity and plant health. Thus, we tested the hypothesis that biochar amendment to different types of soil enhances soil microbial activity, mycorrhizal colonization, plant nutrient availability, plant growth, productivity and reduces GHG when fertilizers are applied monthly or bi-monthly. The experiment consisted of 36 experimental units (e.u.) randomized in a complete block design with 3 replicates. The following organic soils were investigated: 1) a loam, 2) a sandy loam, 3) a sandy soil, 4) a muck soil, 5) a reconstituted organic soil with 40% air porosity and 6) a peat soil amended with sawdust. Half of the e.u. were amended with 10-20% (v/v) biochar (balsam fir + white and black spruces). Tomato plants 'Trust' were cultivated during three growing seasons (February/May to October 2012, 2013, and 2014). The crop was fertilized at 4-week (May to July) and 2-week (August to October) intervals using certified organic amendments. Irrigation was controlled for each soil based on the matric potential measured at 15-cm depth. Effluents from each container were collected and their nutrient content analyzed. Regardless the type of soil, our results showed that biochar amendment increased soil microbial activity expressed by the hydrolysis of fluorescein (FDA) by 14-27% (2013) and 26-41% (2014), and led to lower (~16%, 2012-13) and greater soil CO2 efflux (~11 and 21% when fertilizers were provided at 4- and 2-week intervals, respectively). No significant effect of biochar on root colonisation by mycorrhizae was observed. However, adding biochar to organic soils reduced by 30% (10% v/v) and 50% (20% v/v) the earthworm population. Soils amended with biochar had higher soil mineral content (NO3, P, K, Mg, Fe, Cu, Mn), except for Ca which concentration was equal to control soils and NH4 and Zn which were lower. Biochar amendment reduced by 30% (10% v/v) to 50% (20% v/v) the NO3 content in the leachate. Plant growth, crop yield and leaf mineral content were not influenced by biochar amendment. In conclusion, biochar amendment to different organic soils increased soil biological activity and N retention resulting in lower N leaching and improved crop system sustainability, which might in the long term have beneficial effects on crop performance.
Dorais, M., Gagnon, F., Laurin-Lanctôt, S., Thériault, M., Ménard, C. and Pepin, S. 2017. Short-term improvement of soil biological activity in biochar-amended organic greenhouse tomato crops. Acta Hort. (ISHS) 1164:249-256
CO2 flux, fruit quality, organic farming, nutrient availability, nutrient leaching

Acta Horticulturae