Biochar and compost amendments to a coarse-textured temperate agricultural soil lead to nutrient leaching

Abstract

Organic soil amendments benefit agricultural soils depleted in soil organic matter because they improve soil chemical and biological properties. Biochar and compost, used as organic amendments, differ in their contents of total vs. available nutrients and may therefore differ in their effects on soil properties. The effects of these amendments have seldom been assessed in coarse-textured temperate soils and in no-tillage agriculture. In this study, we conducted a 6-month laboratory experiment with a coarse-textured temperate soil with a history of conventional farming to determine the effects of biochar, compost, and their combination, which were spread evenly on the soil surface, on microbial activity and biomass, and nutrient release and leaching. Both biochar and compost increased microbial activity and nutrient release compared to the no-addition treatment, but compost effects were relatively short term (<two months), and biochar effects were relatively long term (>six months). Biochar and compost had additive effects on all properties when added in combination. Biochar addition to soil increased soil pH, microbial biomass, and the abundance of fungi, G+ bacteria, and actinobacteria after 6 months of incubation compared to the compost treatment and the no-addition treatment. Although biochar was expected to reduce loss of nutrients through leaching, the short exposure time and disturbance of the soil probably hindered its capacity to adsorb nutrients and to thereby limit leaching; as a consequence, the biochar acted only as a slow-release nutrient fertilizer during the 6-month incubation.