深松与免耕频次对黄土旱塬春玉米田土壤团聚体与土壤碳库的影响

【目的】明确减少深松频次对黄土旱塬春玉米田土壤结构与土壤碳库的影响。【方法】2007—2019年在渭北旱塬春玉米田实施不同深松与免耕频次的保护性耕作长期定位试验,以连续深松（S）为对照,设置减少深松频次的免耕与深松结合耕作模式,分别是两年一深松（NS）和三年一深松（NNS)。分析减少深松频次对土壤团聚体、团聚体固碳能力、土壤碳库组成及碳库管理指数的影响。【结果】（1）减少深松频次提高了土壤大土壤团聚体（R_0.25）含量,NNS处理下0—40 cm土层机械稳定性团聚体（DR_0.25）含量提升3.8%,水稳定性团聚体（WR_0.25）含量提升38.9%,NS处理下WR_0.25 提升41.8%。NNS处理降低了团聚体破坏率（PAD）和不稳定团粒指数（E_LT）,平均质量直径（MWD）和几何平均直径（GMD）显著增加13.2%和16.6%。（2）减少深松频次处理下团聚体总固碳能力（TOPC）得到显著提升。NNS处理0—40cm土层平均团聚体固碳能力提升10.8%,但20—30cm土层团聚体固碳能力有所下降。不同粒径团聚体固碳能力表明,<0.25mm粒径团聚体固碳能力较强。（3）NNS处理对0—40cm土层土壤总有机碳（TOC）含量无显著影响,但增加了10—20cm土层TOC含量,减轻了表层土壤有机碳层化效果,降低了30—40cm土层TOC含量,促进了深层土壤有机碳的层化。（4）NNS处理0—40cm土层活性有机碳（EOC）含量显著增加24.9%,EOC含量的增加提升了EOC/TOC比值,增加了碳库活度（A）和碳库活度指数（AI）,相比于S处理,增加碳库管理指数（CPIM）39.8%。【结论】长期连续深松不利于土壤团聚体的形成及土壤碳库的良性循环,而三年一深松的耕作模式有助于降低土壤团聚体的破坏程度,提高碳库管理指数,增强土壤碳库的活度,调节土壤碳库的更新和循环,是适合该地区的耕作模式。

Effects of Subsoiling and No-Tillage Frequencies on Soil Aggregates and Carbon Pools in the Loess Plateau

【Objective】This study was aimed to clarify the effects of reducing the frequencies of subsoiling on the soil structures and soil carbon pool in spring maize fields on the Loess Plateau. 【Method】A long-term positioning experiment of conservation tillage with different frequencies of subsoiling and no-tillage was carried out in spring maize fields on Weibei dryland from 2007 to 2019, with continuous subsoiling (S) as the contrast, which set up combination tillage modes of no-tillage and subsoiling to reduce the frequency of subsoiling: subsoiling once two years (NS) and subsoiling once three years (NNS). The effects of reducing the frequency of subsoiling on soil aggregates, carbon preservation capacity of soil aggregates, soil carbon pool composition and carbon pool management index under different tillage treatments were observed after 12 year continuous experiment. 【Result】(1) Decreasing the frequency of subsoiling improved the content of macroaggregates (R_0.25), the content of 0-40 cm soil layer mechanical-stability aggregates (DR_0.25) increased by 3.8% and water-stable aggregates (WR_0.25) increased by 38.9% under NNS treatment, respectively. NS treatment increased the WR_0.25 by 41.8%. Meanwhile, NNS decreased the destruction rate (PAD) and unstable aggregate index (E_LT) of aggregates, with the mean weight diameter (MWD) and geometrical mean diameter (GMD) significantly increased by 13.3% and 16.6%. (2) The total carbon preservation capacity (TOPC) of the aggregates under NNS and NS was significantly increased. The average carbon sequestration capacity of aggregates in 0-40 cm soil layer under NNS was increased by 10.8%, whereas it was decreased in 20-30 cm soil layer. The carbon preservation ability of aggregates in different sizes indicated that the carbon preservation ability of aggregates with particle size of <0.25 mm was stronger. (3) NNS treatment had no significant effect on the total organic carbon (TOC) content in 0-40 cm soil layer, but increased the TOC content in the 10-20 cm soil layer, reduced stratification effect of surface soil organic carbon, and decreased the TOC content in 30-40 cm soil layer and caused the effect of organic carbon layering in deep soil. (4) The content of active organic carbon (EOC) in the 0-40 cm soil layer under NNS treatment obviously increased by 24.9%. Furthermore, the increase of EOC content lead to higher EOC/TOC ratio, carbon pool activity (A) and carbon pool activity index (AI), with the carbon pool management index (CPIM) increased by 39.8% compared to S. 【Conclusion】Long-term continuous subsoiling was not conducive to the formation of soil aggregates and the cycle of soil carbon pools. While subsoiling once three years tillage mode helped to reduce the degree of damage about soil aggregates, improve the carbon pool management index and adjust the renewal and cycling of soil carbon pool, which was a suitable tillage model for the region.