Cereal yield, yield stability, and nitrous oxide release in European conservation agriculture : A meta-analysis

Context: Conservation Agriculture (CA) aims to enhance the sustainability of agricultural production by minimizing soil disturbance, maintaining soil cover and implementing crop rotations. Despite its potential benefits, the effects of CA on cereal production and soil borne nitrous oxide (N2O) emissions have not yet been investigated at a European scale. Objective: We conducted a comprehensive meta-analysis on the effects of CA on cereal yield, yield stability, and N2O emissions compared with conventional agriculture (CONV). Further, we performed a spatial-explicit analysis across different pedoclimatic conditions in Europe to identify regions more susceptible to negative impacts. Methods: We compiled a dataset of 58 field experiments (a median duration of 7 years) examining the effect of CA on cereal yields (i.e., winter and spring wheat, barley, oats and maize). Additionally, a separate dataset of 11 field experiments (a median duration of 10 years) was assembled to evaluate CA effects on N2O emissions. A weighted meta-analysis was conducted, and Cochran`s Q test was applied to evaluate heterogeneity in effect sizes associated with pedoclimatic conditions and agronomic management practices. Maps for Europe were created to evaluate the spatial patterns of yield changes under two tillage scenarios - minimum tillage (MT) and no tillage (NT) - both adhering to the core principles of CA. Results Overall, CA led to a statistically significant reduction in cereal yields by 3 % (95 % Confidence Interval (CI): 0.2 %–5 %, n = 58) and a decrease in yield stability by 9 % (95 % CI: 3 %–15 %, n = 50) when compared to CONV. A larger yield gap was linked to a higher topsoil clay content and a decreased tillage depth (p < 0.001). For soils with 30 % clay content, the estimated yield gap was 1 % under MT (15 cm depth) and 4.4 % under NT. N2O emissions under CA did not differ from CONV overall (0 %, 95 % CI: –37 % to +67 %, n = 11), but increased significantly when clay content exceeded 30 % (p < 0.0001), though this result relies on the small dataset available. Conclusions Overall, this meta-analysis demonstrated a slight reduction in cereal yields under CA across Europe compared to CONV, coupled with a more pronounced decrease in yield stability, but no impact on N2O emissions. Top soil clay content was a key moderator that amplified both the yield gap and N2O emissions under CA. Consequently, cereal yields in Central and Southern Europe, where the soil clay content is generally higher, are more susceptible to tillage intensity. Thus, MT may offer greater benefits than NT in these regions, provided that the other principles of CA are met. Implications: These findings demonstrate that a one-size-fits-all approach to CA is ineffective and highlights the importance of developing region-specific guidelines. This is particularly important regarding the tillage intensity in clay-rich soils. Recognizing the trade-offs associated with CA practices is critical for their effective and widespread adoption across varying pedoclimatic conditions in Europe.