Effects of the addition of rice-straw-based biochar on leaching and retention of fertilizer N in highly fertilized cropland soils

Abstract

Little is known about the effects of adding crop straw biochar on the leaching and retention of fertilizer nitrogen (N) in intensively managed cropland soils. In this study, the relationship between N leaching and retention from or in soils was investigated after adding 5% (by weight) rice (Oryza sativa L.) straw-derived biochar to four cropland soils with varying properties through an experiment involving 300 mg N kg^{–1 15}N labeled urea and soil column leaching. The ¹⁵N results from the 120-d experiment showed that fertilizer N retention increased by 5.6%~26% (of added N; 8.67~40.0 mg N per column) and fertilizer N leaching decreased by 26%~49% (41.0~76.7 mg N) after biochar was added to the four soils (compared to that in the urea-only treatments). Biochar addition consistently reduced N recovery (retention plus leaching) by 4.5%~38% (7.07~59.5 mg) in the soils. These results indicated that the decreased leaching after the addition of biochar could not be entirely explained by increase of N retention in soils; this suggests that the reduced N leaching may result from both improved N retention in the soil and increased unaccounted-for N (increased gaseous losses). The addition of rice straw-based biochar also significantly affected ammonia (NH₃) volatilization related to crop growth in a pot experiment. Our results suggest a potential negative effect of biochar application on N gaseous losses in heavily fertilized cropland soils, which should be investigated further in future.

Key words:

• ammonium volatilization
• gaseous N losses
• leaching
• retention
• ¹⁵N method.

ACKNOWLEDGMENTS

We sincerely thank anonymous reviewers for their valuable suggestions that have greatly improved the manuscript. This study was funded by the National Natural Science Foundation of China (Grants 41001147 and 41271312), the Knowledge Innovation Program of the Institute of Soil Science, Chinese Academy of Sciences (Grant Y112000010), the Special Fund for Agro-scientific Research in the Public Interest (Grant 200903011) and the National Key Technology R&D Program of China (2013BAD11B00).