Abstract
Cover crops (CC), particularly legumes, are key to promote soil carbon (C) sequestration in no-tillage. Nevertheless, the mechanisms regulating this process need further elucidation within a broad comprehensive framework. Therefore, we investigated effects of CC quality: black oat (Avena strigosa Schreb) (oat), common vetch (Vicia sativa L.) (vetch), and oat + vetch on carbon dioxide-C (CO2-C) emission (124 days) under conventional- (CT), minimum- (MT) and no-tillage (NT) plots from a long-term experiment in Southern Brazil. Half-life time (t1/2) of CC residues and the apparent C balance (ACB) were obtained for CT and NT. We linked our data to long-term (22 years) soil C and nitrogen (N) stocks and crop yield data of our experimental field. Compared to CT, NT increased t1/2 of oat, oat + vetch and vetch by 3.9-, 3.1- and 3-fold, respectively; reduced CO2-C emissions in oat, oat + vetch and vetch by 500, 600 and 642 kg ha−1, respectively; and increased the ACB (influx) in oat + vetch (195%) and vetch (207%). For vetch, CO2-C emission in MT was 77% greater than NT. Legume CC should be preferentially combined with NT to reduce CO2-C emissions and avoid a flush of N into the soil. The legume based-NT system showed the greatest soil C and N sequestration rates, which were significantly and positively related to soybean (Glycine max (L.) Merrill) and maize (Zea mays L.) yield. Soil C (0–90 cm depth) and N (0–100 cm depth) sequestration increments of 1 kg ha−1 corresponded to soybean yield increments of 1.2 and 7.4 kg ha−1, respectively.
Highlights
One-third of the soils worldwide are degraded and losing productivity [1], while only 10% of agricultural lands are improving in soil health [2]
Emission in vetch was 68 and 77% greater than in NT, respectively (Figure 2). These findings indicate that high-quality cover crops (CC) as oat + vetch, and especially vetch, should be preferentially combined with NT, which applies to legume cash crops as soybean
After 123 days, the remaining biomass of oat, oat + vetch and vetch in NT was 9%, 1%, and 11% greater than in conventional tillage (CT), respectively. These results indicate that NT slowed residues decomposition more relevantly within the first 30 days of experiment, where oat, oat + vetch and vetch biomass loss was 44%, 37%, and 67% lower, respectively, compared to CT
Summary
One-third of the soils worldwide are degraded and losing productivity [1], while only 10% of agricultural lands are improving in soil health [2]. Based on the world’s growing population and climate change projections, this scenario may aggravate, threatening food security and urging for the increase of crop yield and mitigation of greenhouse gas (GHG) emissions to the atmosphere [3]. Modeling projections onto a world without agriculture suggest a global soil carbon (C) debt of 133 petagrams (0–2 m depth) due to this activity, with SOC loss rates drastically increasing in the past 200 years [5]. Conservation agriculture (CA) systems that include no-tillage (NT), and the use of cover crops (CC) are efficient tools to mitigate GHG emissions [6], and to enhance soil health and crop yields [7], while addressing societal concerns of food and environmental security.
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