Productivity limits and potentials of the principles of conservation agriculture

Abstract

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 in the future. Conservation agriculture represents a set of three crop management principles that has received strong international support to help address this challenge, with recent conservation agriculture efforts focusing on smallholder farming systems in sub-Saharan Africa and South Asia. However, conservation agriculture is highly debated, with respect to both its effects on crop yields and its applicability in different farming contexts. Here we conduct a global meta-analysis using 5,463 paired yield observations from 610 studies to compare no-till, the original and central concept of conservation agriculture, with conventional tillage practices across 48 crops and 63 countries. Overall, our results show that no-till reduces yields, yet this response is variable and under certain conditions no-till can produce equivalent or greater yields than conventional tillage. Importantly, when no-till is combined with the other two conservation agriculture principles of residue retention and crop rotation, its negative impacts are minimized. Moreover, no-till in combination with the other two principles significantly increases rainfed crop productivity in dry climates, suggesting that it may become an important climate-change adaptation strategy for ever-drier regions of the world. However, any expansion of conservation agriculture should be done with caution in these areas, as implementation of the other two principles is often challenging in resource-poor and vulnerable smallholder farming systems, thereby increasing the likelihood of yield losses rather than gains. Although farming systems are multifunctional, and environmental and socio-economic factors need to be considered, our analysis indicates that the potential contribution of no-till to the sustainable intensification of agriculture is more limited than often assumed.

Mainstreaming conservation agriculture in Malawi: Knowledge gaps and institutional barriers

“…This national situation matches that seen for the African smallholder context more widely (e.g. Giller et al, 2009Giller et al, , 2015, notably in the ability of CA to enhance crop yields without being linked to enhanced agricultural inputs (Pittelkow et al, 2015). Changing the national dynamic of CA communications is vital, to move -to more inclusive planning processes that assess how best to use CA practices as part of an integrated set of actions capable of leading to agricultural development and enhanced adaptive capacity to climatic variability.…”

“…Despite enthusiasm for CA across levels, uncertainty around performance and trade-offs associated with CA practice and its compatibility with diverse livelihood strategies and varied agro-ecological conditions have caused some to question its universal efficacy (e.g. Giller et al, 2009Giller et al, , 2015Andersson and Giller, 2012;Powlson et al, 2014;Rosenstock et al, 2014;Pittelkow et al, 2015). This has led to greater recognition of the need for context-specific guidance on CA as part of an integrated suite of agricultural land management practices (Thierfelder et al, 2016).…”

How to implement biodiversity-based agriculture to enhance ecosystem services: a review

“…For example, positive effects of conservation agriculture, through implementation of its three principles (no-till, permanent soil cover, and crop rotation), may be provided after several years, possibly more than ten. Implementation of only one or two of these principles may lead to negative effects, especially on yields (Pittelkow et al 2014). Furthermore, a single tillage event may significantly damage soil quality, since it can lead to loss of sequestered soil carbon and years of soil restoration (Pisante et al 2015).…”

Zero-tillage as a pathway for sustainable wheat intensification in the Eastern Indo-Gangetic Plains: does it work in farmers’ fields?

“…Based on on-farm trials in Haryana, Mehla et al (2000) estimated a ZT induced yield gain of 15.4 %, which they attributed to timely sowing (9.4 %) and enhanced fertilizer-and water use efficiency, as well as weed suppression (6.0 %). Despite such regional examples that demonstrate the yield advantages of ZT in the irrigated production ecologies of South Asia, the role of ZT and conservation agriculture as foundational technologies for sustainable intensification has recently been drawn into question by a global meta-analysis of paired comparisons of crop yields in ZT and conventionally tilled production systems (Pittelkow et al 2014). The authors conclude that ZT tends to only have yield benefits in rainfed systems and must be combined with residue retention and crop rotation for these benefits to accrue.…”