Combined application of biochar with nitrogen fertilizer improves soil quality and reduces soil respiration whilst sustaining wheat grain yield in a semiarid environment

This study was conducted to investigate the effect of biochar, straw and N fertilizer on soil properties, soil respiration and grain yield of spring wheat (Triticum aestivum L.) in semi-arid Western Loess Plateau of northwestern China. The two carbon sources (straw and biochar) were applied alone or combined with nitrogen fertilizer (urea, 46% nitrogen [N]), whilst the soil without carbon is made up of nitrogen fertilizer applied at 0, 50 and 100 kg N/ha. The experiment was arranged in a randomized complete block design with three replicates and was conducted in 2014, 2015 and 2016 cropping season. Results showed that the greatest grain yields were found with 100 kg N ha-1 fertilization rate under biochar, straw and soils without carbon, but the greatest effect occurred on the biochar amended soils. Biochar amendment produced the greatest grain yield at 1906 kg ha-1, followed by straw treated soils at 1643 kg ha-1, and soils without carbon the lowest at 1553 kg ha-1. This results is supported by the fact that, biochar amended soils (at 0-10 cm) increased soil organic C by 17.14% and 21.65% compared to straw treated soils and soils without carbon respectively. Seasonal soil respirations were between 19.05% and 23.67% lower in BN100 compared with SN50 and CN100. Soil respiration reduced with increasing N fertilization rates under all treatments, but the greatest effect occurred on biochar plots. Biochar amended soils decreased carbon emission by 26.80% and 9.54% compared to straw treated soils and soils without carbon amendment respectively. Increased grain yield and the decreased carbon emission in BN100 translated into greater carbon emission efficiency (2.88 kg kg-1) which was significantly different compared with the other treatments. Combined application of biochar with 100 kg N ha-1 in rainfed spring wheat was a suitable agricultural practice.