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. 2021 Jul 20:9:e11674.
doi: 10.7717/peerj.11674. eCollection 2021.

Effects of fertilizer and biochar applications on the relationship among soil moisture, temperature, and N2O emissions in farmland

Xiao Wang  1 , Ping Lu  2 , Peiling Yang  1 , Shumei Ren  1
Affiliations

Effects of fertilizer and biochar applications on the relationship among soil moisture, temperature, and N2O emissions in farmland

Xiao Wang et al. PeerJ. .

Abstract

Background: Di-nitrogen oxide (N2O) emissions from soil may lead to nonpoint-source pollution in farmland. Improving the C and N content in the soil is an excellent strategy to reduce N2O emission and mitigate soil N loss. However, this method lacks a unified mathematical index or standard to evaluate its effect.

Methods: To quantify the impact of soil improvement (C and N) on N2O emissions, we conducted a 2-year field experiment using biochar as carbon source and fertilizer as nitrogen source, setting three treatments (fertilization (300 kg N ha-1), fertilization + biochar (30 t ha-1), control).

Results: Results indicate that after biochar application, the average soil water content above 20 cm increased by ∼26% and 26.92% in 2019, and ∼10% and 12.49% in 2020. The average soil temperature above 20 cm also increased by ∼2% and 3.41% in 2019. Fertigation significantly promotes the soil N2O emissions, and biochar application indeed inhibited the cumulation by approximately 52.4% in 2019 and 33.9% in 2020, respectively. N2O emissions strongly depend on the deep soil moisture and temperature (20-80 cm), in addition to the surface soil moisture and temperature (0-20 cm). Therefore, we established an exponential model between the soil moisture and N2O emissions based on theoretical analysis. We find that the N2O emissions exponentially increase with increasing soil moisture regardless of fertilization or biochar application. Furthermore, the coefficient a < 0 means that N2O emissions initially increase and then decrease. The aRU < aCK indicates that fertilization does promote the rate of N2O emissions, and the aBRU > aRU indicates that biochar application mitigates this rate induced by fertilization. This conclusion can be verified by the sensitivity coefficient (SCB of 1.02 and 14.74; SCU of 19.18 and 20.83). Thus, we believe the model can quantify the impact of soil C and N changes on N2O emissions. We can conclude that biochar does significantly reduce N2O emissions from farmland.

Keywords: Biochar; Exponential fitting; Fertilization; Multivariate nonlinear fitting; N2O emissions; Sensitivity coefficient; Soil moisture; Soil temperature.

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Conflict of interest statement

The authors declare there are no competing interests.

Figures

Figure 1
Figure 1. The soil water content for each treatment in the depth of 10 cm, 20 cm, 40 cm, 60 cm, and 80 cm during 2019–2020 is presented.
(A), (B), and (C) show the soil water content in RU, BRU, and CK treatments in 2019, respectively; (D), (E), and (F) show the soil water content in RU, BRU, and CK treatments in 2020 respectively.
Figure 2
Figure 2. The soil temperature for each treatment in the depth of 10 cm, 20 cm, 40 cm, 60 cm, and 80 cm during 2019–2020 is presented.
(A), (B), and (C) show the soil temperature for RU, BRU, and CK treatment in 2019, respectively; (D), (E), and (F) show the soil temperature for RU, BRU, and CK treatment in 2020.
Figure 3
Figure 3. N2O emissions in the maize growth stage is presented.
(A) and (B) show the N2O emissions in 2019 and 2020, respectively.
Figure 4
Figure 4. The fitting about WFPS, soil temperature, and N2O emissions based on MNF-DR analysis for each treatment during 2019–2020 is presented.
(A) and (E) represents the measured data of the three treatments (RU + BRU + CK) we used for MNF-DR analysis in 2019 and 2020, respectively; (B) and (F) represents the measured data of RU we used for MNF-DR analysis in 2019 and 2020, respectively; (C) and (G) represents the measured data of BRU we used for MNF-DR analysis in 2019 and 2020, respectively; (D) and (H) represents the measured data of CK we used for MNF-DR analysis in 2019 and 2020, respectively.
Figure 5
Figure 5. The fitting about WFPS and N2O emissions based on the exponential model for each treatment during 2019–2020 is presented.
(A) and (D) represents the measured data of RU we used for the exponential model in 2019 and 2020, respectively; (B) and (E) represents the measured data of BRU we used for the exponential model in 2019 and 2020, respectively; (C) and (F) represents the measured data of CK we used for the exponential model in 2019 and 2020, respectively.
Figure 6
Figure 6. Determinants of soil N2O emissions.
See this image and copyright information in PMC

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