Biochar reduced nitrate leaching and improved soil moisture content without yield improvements in a four-year field study

•Over the four years crop yields were never increased by biochar.•In the first months biochar caused manganese deficiency in maize.•Biochar increased nitrate retention in the topsoil 0–15cm where it was incorporated.•Biochar could not alleviate N uptake limitation under drought conditions.•The same soil and biochar produced different results in a greenhouse compared to the field study.