Soil nematode trophic structure and biochar addition in recently converted boreal lands

Context. Climate change facilitated expansion of agriculture into northern regions increases the amount of Podzol dominated farmland. Biochar can improve poor growing conditions in soils. There are no universally accepted soil quality indicators for assessing the sustainability of expanding and intensifying boreal farming. Changes in the soil community structure can inform on soil functional status and the impact of management. Aims. We assessed the impacts of biochar added to recently converted agricultural land on soil nematodes. We hypothesised that biochar addition would increase soil pH, correlate with total nematode abundance, and favour bacterivores over fungivores. Methods. Biochar was added to soil at 10-80 Mg C ha(-1) rates. Physicochemical soil properties, crop yields, nematode community trophic composition, trophic group ratios, and diversity indices were assessed. Key results. Soil quality and fertility were improved with biochar, critically through increasing pH from 4.8 to 5.5. The interactions between pH, available metals, and micro-nutrients were related to biochar rate. Biochar was associated with increased bacterivore abundance (CI90 of 328 +/- 132 vs 618 +/- 50 individuals) indicating accelerated SOM degradation, and increased omnivore abundance (CI90 of 13 +/- 17 vs 33 +/- 7 individuals) indicating a more resilient community. Changes to Podzol quality may be most reliably indicated by bacterivore abundance and community complexity than by ratios and diversity indices. Conclusions. Biochar application improved soil quality as suggested by nematode community structure. Implications. Biochar application may be recommended to improve Podzol quality and fertility. Soil nematodes can indicate relative changes to Podzol quality.