After-Effects of Hydrochar Amendment on Water Spinach Production, N Leaching, and N2O Emission from a Vegetable Soil under Varying N-Inputs

Biochar use in agriculture brings significant agronomic and environmental co-benefits, which are a function of biochar and crop types and nitrogen (N) rates. We here conducted a soil column experiment to evaluate the after-effects of hydrochar amendment at 0.5 and 2.0 wt% on vegetable production, N recovery and losses via leaching and nitrous oxide (N2O) emission from water-spinach (Ipomoea aquatica Forsk)-planted vegetable soil receiving three N inputs (120, 160, and 200 kg/ha). The results showed that hydrochar with 2.0 wt% significantly (p < 0.05) improved the biomass yield of water spinach, receiving 120-160 kg N/ha by 11.6-14.2%, compared with no change in the hydrochar treatment. Hydrochar had no effect on total N content of water spinach, and only increased the total N recovery under 2.0 wt% given hydrochar amended treatment with 120 kg N/ha. Neither pH or EC of leachate was changed with N reduction or hydrochar application. However, in some cases, hydrochar changes the NH4+, NO3- and total N concentrations in leachate. When applied at 2.0 wt%, hydrochar significantly (p < 0.05) increased total N leaching losses by 28.9% and 57.1%, under 120 and 160 kg N/ha plot, respectively. Hydrochar applied at two rates increased the N2O emissions by 109-133% under 200 kg N/ha but decreased them by 46-67% under 160 kg N/ha. Therefore, after three years of application, hydrochar still improves the production of leafy vegetable, but the impacts on N leaching and N2O emission vary, depending on inorganic N and hydrochar application rates.

Automated summary

Biochar use in agriculture has significant effects on crop production and nitrogen recovery, but the impacts on nitrogen leaching and N2O emissions vary depending on the application rates and methods.