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Productivity limits and potentials of the principles of conservation agriculture

Cameron M. Pittelkow, Xinqiang Liang, Bruce A. Linquist, Kees Jan van Groenigen, Juhwan Lee, Mark E. Lundy, Natasja van Gestel, Johan Six, Rodney T. Venterea, Chris van Kessel
Nature 2015 v.517 no.7534 pp. 365-368
agroecosystems, climate, climate change, conventional tillage, cover crops, crop residues, crop rotation, crop yield, disturbed soils, environmental impact, meta-analysis, no-tillage, planting, small-scale farming, socioeconomic factors, South Africa, South Asia
One of the primary challenges of our time is to feed a growing and more demanding world population with reduced external inputs and minimal environmental impacts, all under more variable and extreme climate conditions of the future. Conservation agriculture (CA) represents a set of three crop management principles (direct planting of crops with minimum soil disturbance (i.e. no-till), permanent soil cover by crop residues or cover crops, and crop rotation) that has received strong international support to help address this challenge, with recent CA efforts focusing on smallholder farming systems in Sub-Saharan Africa and South Asia. However, CA is highly debated, both with respect to its effects on crop yields and its applicability in different farming contexts. Here, we conducted a global meta-analysis of 5551 paired yield observations from 613 studies comparing no-till, the original and central concept of CA, to conventional tillage practices across 33 crops and 60 countries. Overall, our results show that no-till reduces yields on average by 4.7% (95% CI: -5.7 to -3.7%) . Importantly, we found that when the other two CA principles are implemented, the negative impacts of no-till are minimized and it takes less time for no-till to match conventional yields following no-till adoption. Moreover, in rainfed agroecosystems under dry climates, no-till in combination with the other two principles significantly increases productivity. While farming systems are multifunctional and both environmental and socio-economic factors need to be considered, our meta-analysis indicates that no-till is an effective longer-term climate change adaptation strategy in ever-becoming-drier regions of the world, but only when it is integrated with residue retention and crop rotation.