Effects of biochar, urea and their co‐application on nitrogen mineralization in soil and growth of Chinese cabbage

Abstract

AbstractExperiments were conducted to study the effect of soil applications of kunai grass (Imperata cylindrica) biochar (0 and 10 t/ha) and laboratory grade urea (0, 200 and 500 kg N/ha) and their co‐application on nitrogen (N) mineralization in an acid soil. The results of an incubation study showed that the biochar only treatment and co‐application with urea at 200 kg N/ha could impede transformation of urea to ammonium‐N (NH4+‐N). Soil application of biochar together with urea at 500 kg N/ha produced the highest nitrate‐N (NO3−‐N) and mineral N concentrations in the soil over 90 days. Co‐application of urea N with biochar improved soil N mineralization parameters such as mineralization potential (NA) and coefficient of mineralization rate (k) compared to biochar alone. In a parallel study performed under greenhouse conditions, Chinese cabbage (Brassica rapa L. ssp. chinensis L.) showed significantly greater (P < 0.05) marketable fresh weight, dry matter production and N uptake in soil receiving urea N at 500 kg/ha or co‐application of biochar with urea N compared to the control. Application of biochar only or urea only at 200 kg N/ha did not offer any short‐term agronomic advantages. The N use efficiency of the crop remained unaffected by the fertilizer regimes. Applications of biochar only at 10 t/ha did not offer benefits in this tropical acid soil unless co‐applied with sufficient urea N.