Nitrification, acidification, and nitrogen leaching from subtropical cropland soils as affected by rice straw-based biochar: laboratory incubation and column leaching studies
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Few studies have examined the effects of biochar on nitrification of ammonium-based fertilizer in acidic arable soils, which contributes to NO3 − leaching and soil acidification.
Materials and methods
We conducted a 42-day aerobic incubation and a 119-day weekly leaching experiment to investigate nitrification, N leaching, and soil acidification in two subtropical soils to which 300 mg N kg−1 ammonium sulfate or urea and 1 or 5 wt% rice straw biochar were applied.
Results and discussion
During aerobic incubation, NO3 − accumulation was enhanced by applying biochar in increasing amounts from 1 to 5 wt%. As a result, pH decreased in the two soils from the original levels. Under leaching conditions, biochar did not increase NO3 −, but 5 wt% biochar addition did reduce N leaching compared to that in soils treated with only N. Consistently, lower amounts of added N were recovered from the incubation (KCl-extractable N) and leaching (leaching plus KCl-extractable N) experiments following 5 wt% biochar application compared to soils treated with only N.
Incorporating biochar into acidic arable soils accelerates nitrification and thus weakens the liming effects of biochar. The enhanced nitrification does not necessarily increase NO3 − leaching. Rather, biochar reduces overall N leaching due to both improved N adsorption and increased unaccounted-for N (immobilization and possible gaseous losses). Further studies are necessary to assess the effects of biochar (when used as an addition to soil) on N.
KeywordsAcidic arable soil Ammonium-based fertilizer Nitrification NO3− leaching Rice straw biochar Soil pH
We sincerely thank the anonymous reviewers for their valuable suggestions that have greatly improved the manuscript. The authors acknowledge the financial support provided by the National Natural Science Foundation of China (grants 41001147 and 41271312), the Knowledge Innovation Program of the Institute of Soil Science of Chinese Academy of Sciences (grant Y112000010), and National Key Technology R&D Program of China (SQ2011BAJY3104 and 2013BAD11B00).
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