Co-application of straw incorporation and biochar addition stimulated soil N2O and NH3 productions

Abstract

Nitrous oxide (N2O) and ammonia (NH3) volatilization (AV) are the major pathways of nitrogen (N) loss in soil, and recently, N2O and NH3 mitigation has become urgently needed in agricultural systems worldwide. However, the influence of straw incorporation (SI) and biochar addition (BC) on N2O and NH3 emissions are still unclear. To fill this knowledge gap, a soil column experiment was conducted with two management strategies using straw - straw incorporation (S1) and straw removal (S0) - and four biochar application rates (0 (C0), 15 (C1), 30 (C2), and 45 t ha-1 (C3)) to evaluate the impacts of their interactions on N2O and NH3 emissions. The results showed that NO3--N concentration and pH was the major contributors to affect the N2O and NH3 losses. Without biochar addition, N2O emissions was decreased by 59.6% (P<0.05) but AV was increased by 97.3% (P<0.05) under SI when compared to SR. Biochar was beneficial for N2O mitigation when straw was removed, but increased N2O emission by 39.4%-83.8% when straw was incorporated. Additionally, biochar stimulated AV by 27.9%-60.4% under S0 and 78.6%-170.3% under S1. Consequently, SI was found to significantly interact with BC in terms of affecting N2O (P<0.001) and NH3 (P<0.001) emissions; co-application of SI and BC promoted N2O emissions and offset the mitigation potential by SI or BC alone. The indirect N2O emissions caused by AV, however, might offset the reduction of direct N2O caused by SI or BC, thus leading to an increase in overall N2O emission. This paper recommended that SI combined BC at the amount of 8.2 t ha-1 for maintaining a lower overall N2O emission for future agriculture practices, but the long-term impacts of straw incorporation and biochar addition on the trade-off between N2O and NH3 emissions and reactive N losses should be further examined and assessed.

Fig 1

(a) Design drawing of pot experiment, (b) schedule of fertilization and irrigation managements and air temperature, and (c) photograph of the indoor experiment. SI: straw incorporation; S0: straw removal; BC: biochar addition; B0: without biochar.

Fig 2

The emission fluxes of N₂O and NH₃ under conditions of either straw incorporation (a, b) and straw removal (c, d) with different addition amounts of biochar. Error bars denote standard errors. C0: without biochar; C1: biochar applied at 15 t ha⁻¹; C2: biochar applied at 30 t ha⁻¹; C3: biochar applied at 45 t ha⁻¹.

Fig 3. The influence of straw and biochar on N₂O and NH₃ emissions.

Error bars denote standard errors. * P<0.05. Definitions of C0, C1, C2, and C3 are given in caption of Fig 2.

Fig 4. Soil temperature under different treatments during the experimental period.

Error bars denote standard errors. Definitions of C0, C1, C2, and C3 are given in caption of Fig 2.

Fig 5. WFPS under different treatments during the experimental period.

Error bars denote standard errors. Definitions of C0, C1, C2, and C3 are given in caption of Fig 2.

Fig 6. Soil NO₃⁻−N, NH₄⁺−N, total N, and organic matter content in different soil layers under different treatments.

Error bars denote standard errors. The different letters in the same soil layer indicate a significant difference (P<0.05) with Turkey’s multiple range test of different amounts of biochar addition either under straw incorporation or not. Definitions of C0, C1, C2 and C3 are given in caption of Fig 2.

Fig 7

(a) Redundancy analysis of the influence and the contribution (b) of soil properties on N2O and NH3 losses.

Fig 8. Correlation analysis between biochar addition, N₂O, NH_3, and measured variables under straw incorporation or removal.

Each bubble with * indicates a significant correlation at P<0.05.

Fig 9. The relationship between overall N₂O emission and biochar addition under straw incorporation (S1) and removal (S0).

Error bars denote standard errors.