Effects of biochar application on soil nitrogen and phosphorous leaching loss and oil peony growth

The control of soil nutrient loss to lighten non-point source pollution to water body and improve soil fertility is a global problem. Biochar application to soil is widely considered as an effective method to improve soil fertility and reduce nutrient loss. However, the effect of biochar application to barren karst yellow soil in global karst regions on the loss of nitrogen (N) and phosphorous (P) and the growth of oil peony (an important woody oil crop) remains unclear. We conducted the indoor leaching experiments, in-site observation of the N and P loss with surface runoff under three types of rains and the comparative experiment of oil peony growth when the different amount of biochar was applied to karst yellow soil. The results indicated that soil pH, total nitrogen (TN), total phosphorous (TP), available N and available P contents in the soil increased with an increase of biochar application under indoor simulation but the loss of leaching solution decreased. 2 kg/m² biochar application caused the least loss of TP, TN, nitrate nitrogen (NN) and ammonia nitrogen (AN) with the leaching solution compared with 0, 4 and 6 kg/m² application. The rapid and slow attenuation of P and N concentrations, respectively, were observed in karst yellow soil with biochar application. The N/P change in leaching solution showed a parabolic form. Under natural rainfall, 4 kg/m² biochar application had the best effect on a reduction of TP, TN and AN loss in surface runoff. Rainstorm caused AN and TP large loss but rainstorm, heavy and moderate rains all easily caused NN large loss. 4 kg/m² biochar application had the best effect on the growth of plant height and base diameter, leaf SPAD and N and P content in organs in the fertilized area but 6 kg/m² in the unfertilized area. Biochar application effectively improved the fertility of karst yellow soil, reduced the loss of N and P with vertical leaching and surface runoff, and promoted the growth of oil peony. This study provides new knowledge for biochar application.