ABSTRACT

Soil acts as a natural source and sink for greenhouse gases (GHG) that are responsible for global warming and climate change. As the agricultural sector has an important impact on GHG (e.g., CO₂, CH₄, N₂O) emissions, the definition of mitigation strategies is needed, especially for the Mediterranean climate areas that appear most vulnerable to climate change. The introduction of perennial legumes, such as alfalfa (Medicago sativa L.), falls within this scope, but it requires the application of a termination method aimed at reduction of GHG emissions. With the aim of assessing the short-term effects of two different alfalfa termination methods (Tillage vs No tillage plus herbicide), we defined the hypothesis that alfalfa termination by Tillage will increase soil GHG emissions compared to its termination by No tillage plus herbicide. Soil CO₂, CH₄ and N₂O emissions were monitored over ~2 months (71 days; October–December, 2017) following alfalfa termination, using closed static chambers. The soil total GHG emissions after 71 days were significantly different for Tillage and No tillage plus herbicide: 311.90 ±21.21 versus 195.89 ±11.14 g CO₂ equivalent m⁻², respectively. For both termination methods, CO₂ (up to a maximum value of 1.24 ±0.18 and 0.65± 0.07 kg C-CO₂ ha⁻¹ h⁻¹, respectively) was the greatest contributor to the total soil GHG emissions (about 96%), compared to N₂O (up to a maximum value of 0.37 ±0.13 and 0.31± 0.10 g N-N₂O ha⁻¹ h⁻¹, respectively) and CH₄ (up to a maximum value of −0.01 ±0.03 and 0.07 ±0.03 g C-CH₄ ha⁻¹ h⁻¹, respectively). These data suggest that over the short term, legume perennial crop termination by No tillage plus herbicide better supports the purpose of climate regulations.

摘要

土壤是导致全球变暖和气候变化的温室气体 (GHG) 的天然来源和汇。由于农业部门对温室气体（例如，CO ₂、CH ₄、N ₂ O）排放有重要影响，因此需要定义缓解策略，特别是对于似乎最容易受到气候变化影响的地中海气候区。多年生豆科植物，如紫花苜蓿 ( Medicago sativa L.)的引入属于这一范围，但需要采用旨在减少温室气体排放的终止方法。为了评估两种不同的苜蓿终止方法（耕作与免耕加除草剂），我们定义了这样一个假设，即与免耕加除草剂终止相比，耕作终止苜蓿会增加土壤温室气体排放。在苜蓿终止后约 2 个月（71 天；2017 年 10 月至 12 月）内，使用封闭式静态室监测土壤 CO ₂、CH ₄和 N ₂ O 排放。耕作和免耕加除草剂在 71 天后的土壤总温室气体排放量显着不同：分别为 311.90 ±21.21和195.89 ±11.14 g CO ₂当量 m ^-2。对于这两种终止方法，CO ₂（最大值为 1.24 ±0.18 和 0.65± 0.07 kg C-CO ₂ ha ^-1h ^-1分别是土壤温室气体总排放量的最大贡献者（约 96%），与 N ₂ O相比（最大值为 0.37 ±0.13 和 0.31± 0.10 g NN ₂ O ha ^-1 h ^{- 1} )和CH ₄ (分别高达-0.01 ±0.03和0.07 ±0.03 g C-CH ₄ ha ^-1 h ^-1的最大值)。这些数据表明，在短期内，免耕加除草剂终止豆科多年生作物可以更好地支持气候调节的目的。