Abstract
Reduction of soil fertility and production efficiency resulting from excessive application of chemical fertilizers is universal in rapeseed-growing fields. The main objective of our study was to assess the effects of biochar combined with nitrogen fertilizer reduction on soil aggregate stability and rapeseed yield and to identify the relationship between yield and soil aggregate stability. A two-factor field experiment (2017–2019) was conducted with biochar (0 (C0), 10 (C10), 20 (C20) and 40 t·ha−1 (C40)) and nitrogen fertilizer (180 (N100), 144 (N80) and 108 kg N·ha−1 (N60)). Experimental results indicated that under N100 and N80 treatments, C10 significantly increased the macro-aggregates (R0.25), mean weight diameter (MWD) and geometric mean diameter (GMD) of soil water stable aggregate by 14.28%–15.85%, 14.88%–17.08% and 36.26%–42.22%, respectively, compared with C0. Besides, the overall difference of the soil water-stable aggregate content in 2–5 mm size range among nitrogen treatments was significant under the application of C10, which increased by 17.04%–33.04% compared with C0. Total organic carbon (TOC) in R0.25 of soil mechanical-stable aggregates was basically all increased after biochar application, especially in 0.25–1 mm and 1–2 mm aggregates, and had an increasing trend with biochar increase. C10 significantly increased rapeseed yield by 22.08%–45.65% in 2019, compared with C0. However, the reduction of nitrogen fertilizer reduced the two-year average rapeseed yield, which decreased by 11.67%–31.67% compared with N100. The highest yield of rapeseed was obtained by N100C10 in two consecutive years, which had no statistical difference with N80C10. However, the two-year yields of N80C10 were all higher than those of N100C0 with increase rate of 16.11%, and which would reduce 35.43% nitrogen fertilizer in the case of small yield difference, compared with the highest yield (2.67 t·ha−1) calculated by multi-dimensional nonlinear regression models. The regression analysis indicated R0.25, MWD and GMD had the strong positive associations with rapeseed yield, whereas percentage of aggregate destruction (PAD0.25) had a significant negative correlation with rapeseed yield. This study suggests that the application of biochar into upland purple soil could improve soil structure, increase the content of TOC in macro-aggregates under nitrogen fertilizer reduction as well as replace part of nitrogen fertilizer to achieve relatively high rapeseed yield.
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Claims 14
Claim · model-written summary
C10 under N100 and N80 significantly increased soil macro-aggregates by 14.28%–15.85% relative to C0.
- Treatment
- C10e0
- Outcome
- macro-aggregates (R0.25)e0
- Direction
- increasede0
- Value
- 14.28%–15.85%e0
- Comparator
- C0e0
Not reportedTaxon
Verbatim
e0“under N100 and N80 treatments, C10 significantly increased the macro-aggregates (R0.25), mean weight diameter (MWD) and geometric mean diameter (GMD) of soil water stable aggregate by 14.28%–15.85%, 14.88%–17.08% and 36.26%–42.22%, respectively, compared with C0”
Claim · model-written summary
C10 under N100 and N80 increased soil aggregate mean weight diameter by 14.88%–17.08% relative to C0.
- Treatment
- C10e0
- Outcome
- mean weight diameter (MWD)e0
- Direction
- increasede0
- Value
- 14.88%–17.08%e0
- Comparator
- C0e0
Not reportedTaxon
Verbatim
e0“under N100 and N80 treatments, C10 significantly increased the macro-aggregates (R0.25), mean weight diameter (MWD) and geometric mean diameter (GMD) of soil water stable aggregate by 14.28%–15.85%, 14.88%–17.08% and 36.26%–42.22%, respectively, compared with C0”
Claim · model-written summary
C10 under N100 and N80 increased soil aggregate geometric mean diameter by 36.26%–42.22% relative to C0.
- Treatment
- C10e0
- Outcome
- geometric mean diameter (GMD)e0
- Direction
- increasede0
- Value
- 36.26%–42.22%e0
- Comparator
- C0e0
Not reportedTaxon
Verbatim
e0“under N100 and N80 treatments, C10 significantly increased the macro-aggregates (R0.25), mean weight diameter (MWD) and geometric mean diameter (GMD) of soil water stable aggregate by 14.28%–15.85%, 14.88%–17.08% and 36.26%–42.22%, respectively, compared with C0”
Claim · model-written summary
Under C10, nitrogen treatments differed significantly in 2–5 mm water-stable aggregate content, which increased 17.04%–33.04% relative to C0.
- Treatment
- C10e0
- Outcome
- soil water-stable aggregate content in 2–5 mm size rangee0
- Direction
- increasede0
- Value
- 17.04%–33.04%e0
- Comparator
- C0e0
Not reportedTaxon
Verbatim
e0“the overall difference of the soil water-stable aggregate content in 2–5 mm size range among nitrogen treatments was significant under the application of C10, which increased by 17.04%–33.04% compared with C0”
Claim · model-written summary
Biochar application generally increased total organic carbon in soil mechanical-stable aggregates, especially 0.25–1 mm and 1–2 mm aggregates, with an increasing trend as biochar increased.
- Treatment
- biochar applicatione0
- Outcome
- Total organic carbon (TOC) in R0.25 of soil mechanical-stable aggregatese0
- Direction
- increasede0
- Qualifier
- especially in 0.25–1 mm and 1–2 mm aggregatese0
Not reportedTaxonComparator
Verbatim
e0“Total organic carbon (TOC) in R0.25 of soil mechanical-stable aggregates was basically all increased after biochar application, especially in 0.25–1 mm and 1–2 mm aggregates, and had an increasing trend with biochar increase.”
Claim · model-written summary
C10 significantly increased rapeseed yield by 22.08%–45.65% in 2019 relative to C0.
Verbatim
e0“C10 significantly increased rapeseed yield by 22.08%–45.65% in 2019, compared with C0.”
Claim · model-written summary
Reducing nitrogen fertilizer decreased two-year mean rapeseed yield by 11.67%–31.67% relative to N100.
Verbatim
e0“the reduction of nitrogen fertilizer reduced the two-year average rapeseed yield, which decreased by 11.67%–31.67% compared with N100.”
Claim · model-written summary
N100C10 gave the highest rapeseed yield in both years.
Verbatim
e0“The highest yield of rapeseed was obtained by N100C10 in two consecutive years”
Claim · model-written summary
Yield under N100C10 was not statistically different from N80C10.
Verbatim
e0“The highest yield of rapeseed was obtained by N100C10 in two consecutive years, which had no statistical difference with N80C10.”
Claim · model-written summary
N80C10 yielded 16.11% more than N100C0 over two years.
Not reportedTaxon
Verbatim
e0“the two-year yields of N80C10 were all higher than those of N100C0 with increase rate of 16.11%”
Claim · model-written summary
The regression model indicated a highest yield of 2.67 t·ha−1 with a 35.43% reduction in nitrogen fertilizer.
Not reportedTaxon
Verbatim
e0“would reduce 35.43% nitrogen fertilizer in the case of small yield difference, compared with the highest yield (2.67 t·ha−1) calculated by multi-dimensional nonlinear regression models”
Claim · model-written summary
Soil macro-aggregate content, mean weight diameter and geometric mean diameter were strongly positively associated with rapeseed yield.
Not reportedTaxonSettingDirection
Verbatim
e0“R0.25, MWD and GMD had the strong positive associations with rapeseed yield”
Claim · model-written summary
Aggregate destruction percentage was significantly negatively correlated with rapeseed yield.
Not reportedTaxonSettingDirection
Verbatim
e0“percentage of aggregate destruction (PAD0.25) had a significant negative correlation with rapeseed yield”
Claim · model-written summary
The authors suggest biochar in upland purple soil can improve soil structure and macro-aggregate carbon under nitrogen reduction while partly replacing fertilizer to maintain relatively high rapeseed yield.
Verbatim
e0“the application of biochar into upland purple soil could improve soil structure, increase the content of TOC in macro-aggregates under nitrogen fertilizer reduction as well as replace part of nitrogen fertilizer to achieve relatively high rapeseed yield”
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