Interaction of Biochar Addition and Nitrogen Fertilizers on Wheat Production and Nutrient Status in Soil Profiles

To investigate the responses of crop production and soil profile nutrient status to biochar (BC) application, we conducted a soil column experiment considering two BC addition rates (0.5 and 1.5 wt% of the weight of 0-20 cm topsoil) combined with two nitrogen (N) input levels (low N: 144 kg ha^-1, LN; high N: 240 kg ha^-1, HN). The results showed that BC application increased the soil pH. The soil pH of the 0-10 cm profile under LN and the 20-40 cm profile under HN were both significantly increased by 0.1-0.2 units after BC addition. Under LN, BC addition significantly increased NH₄⁺-N (17.8-46.9%), total N (15.4-38.4%), and soil organic carbon (19.9-24.0%) in the 0-10 cm profile, but decreased NH₄⁺-N in the 20-30 cm soil profile and NO₃^--N in the 10-30 cm profile by 13.8-28.5% and 13.0-34.9%, respectively. BC had an increasing effect on the available phosphorus, the contents of which in the 10-20 and 30-40 cm soil profiles under LN and 20-30 cm profile under HN were significantly elevated by 14.1%, 24.0%, and 23.27%, respectively. However, BC exerted no effect on the available potassium in the soil profile. BC had a strong improving effect (15.3%) on the wheat yield, especially the N144 + BC0.5% treatment, which could be compared to the HN treatment, but there was no yield-increasing effect when high N fertilizer was supplied. In summary, BC improved the fertility of agriculture soil (0-20 cm) with wheat. In particular, low N inputs together with an appropriate rate of BC (0.5 wt%) could not only achieve the low inputs but also the high outputs in wheat production. In future study, we will compare the effects of multiple doses of N and BC on soil fertility and crop production.