Effects of Fresh and Aged Maize Straw-Derived Biochars on Inorganic Nitrogen Adsorption in Aqueous Solution and Leaching from Calcareous Clay Soil

摘要

Biochar’s production and application in soils has been suggested as a means of abating climate change by sequestering carbon, while simultaneously providing energy and increasing crop yields. However, little is known about the effects of aged biochars on ammonium (NH 4 + ) and nitrate (NO 3 - ) adsorption and leaching from arable calcareous clay soil. Based on the physicochemical analyses of the fresh and spontaneously aged maize straw-derived biochars (prepared at 400 and 600 o C, designated as F400, F600, A400, and A600, respectively), the effects of the four kinds of biochars on NH 4 + and NO 3 - adsorption in aqueous solution and their leaching from calcareous clay soil were explored. Results showed that the aged biochars (A400 and A600) decreased pH and mean pore size, but increased carboxyl amount and specific surface area compared with the fresh biochars (F400 and F600). NH 4 + adsorption capacity of the biochars was as follows A400 > A600/F400 > F600, with the maximum of 4.20 mg NH 4 + -N/g biochar at A400. Though biochar NO 3 - adsorption capacity showed the similar trend as NH 4 + , the variations were significantly large, indicating the instability of NO 3 - adsorption by biochar. The column leaching experiment showed that both the fresh and aged biochars inhibited inorganic N leaching. For NH 4 + , though all the biochars postponed the occurrence of leaching peak compared with control, A400 and A600 showed much stronger ability than F400 and F600 to delay the leaching peak occurring. However, for NO 3 - , the leaching peak of A400 and A600 occurred at the same leaching event as control, while F400 and F600 even brought the leaching peak forward. Furthermore, the distribution profiles of potential ammonia-oxidation rate and ammonia-oxidizing bacteria amount in soil column after leaching indicated that A400 and A600 possessed relatively stronger ability than F400 and F600 to retain NH 4 + transportation into the deep layers of soil column. In all, the spontaneous aging process enhanced the inorganic N adsorption capacity and retention ability of maize straw-derived biochars.