Impact of manure and biochar additions on annual crop growth, nutrient uptake, and fate of 15N-labelled fertilizer in two contrasting temperate prairie soils after four years

Abstract

Liquid hog manure (LHM) and solid cattle manure (SCM) co-applied with biochar could beneficially influence soil nitrogen (N) and phosphorus (P) dynamics. A split-plot design was used at two sites (Brown and Black) in Saskatchewan to assess LHM and SCM (100 kg N·ha−1) applied alone or in combination with biochars (8 Mg carbon·ha−1) produced using slow or fast pyrolysis. Crop growth and nutrient uptake, along with fertilizer 15N recovery, were followed over four years in a cereal–oilseed rotation. Crop growth on the Brown soil was more responsive to the treatments than the Black soil, reflecting lower fertility of the Brown soil. The manure and biochar, applied alone or in combination, had little impact on available soil P. Manure and biochar effects on crop growth and nutrient uptake were attributed to temporal effects on soil N immobilization–mineralization influencing plant-available soil N. A negative impact of the fast pyrolysis biochar on growth and plant uptake was observed and attributable to its greater labile-carbon content, which likely promoted soil N immobilization. Synergism observed between SCM and the slow pyrolysis biochar may reflect enhanced net SCM-N mineralization and increased water-holding capacity. The majority (55%–80%) of plant 15N recovery occurred during the first year, with 86% of fertilizer 15N conserved within the soil–plant system after four years. Greater (40%) plant 15N recovery without biochar addition, coupled with increased (38%) soil 15N recovery with added biochar, suggests biochar-related immobilization and (or) sorption in the biochar-amended soils.