Effects of biochar application depth on nitrate leaching and soil water conditions

ABSTRACT

Nitrate leaching from farmland pollutes the surrounding environment, such as groundwater, causing health hazards to inhabitants. To mitigate the leaching, biochar can be applied. The effect of biochar application differs depending on the application depth; however, the effect of the application depth remains unclear. To evaluate the effect, we conducted a pipe experiment with no plant using bagasse biochar with four treatments: no biochar application, surface application (0−5 cm), plow layer application (0−30 cm), and subsurface application (25−30 cm). The results showed that surface and plow layer applications reduced nitrate leaching, whereas subsurface application did not affect leaching. This difference was due to changes in the soil water movement and water budget. Surface application reduced evaporation, inducing increases in both drainage and the amount of water in the pipe. The increased amount of water might contribute to an increase in the amount of nitrogen in the pipe, reducing the leaching. Plow layer application increased evaporation, leading to decreased drainage and nitrate leaching. Subsurface application did not affect drainage and nitrate leaching; however, the change in the volumetric water content at a depth of 10 cm was the most significant among the treatments. Our study indicated that, although the same amount of biochar was applied, the effect of biochar application differs depending on the application depth.

GRAPHICAL ABSTRACT

KEYWORDS:

• Water budget
• groundwater pollution
• biochar amendment
• bagasse biochar
• soil layer

Acknowledgments

We thank Yasuki Shikina, Masahide Maetsu, Yuto Hateruma, and Akiko Sawa for their help with the experimental apparatuses and sampling and Tokuko Sekine for measuring the soil physical properties. We congratulate Yasuki Shikina, Masahide Maetsu and Yuto Hateruma on receiving the Award for Creativity by the Ministry of Education, Culture, Sports, Science and Technology, Japan.

Disclosure statement

No potential conflict of interest was reported by the author(s).

Data availability statement

The data that support the findings of this study are available from the corresponding author, K.H., upon reasonable request.

Additional information

Funding

This work was supported by Japan International Research Center for Agricultural Sciences under operating cost subsidy.