Application of Data Meta-Analysis for Smallholder Conditions.

Increasing accessibility of papers and data sets have caused an upsurge in the use of meta-analyses in agricultural research. Meta-analysis, a statistical technique for combining and analyzing the results from 10 to hundreds of studies, has been practiced for decades, and in some fields, such as medicine, its use is routine. Analyzing a large set of experiments allows drawing general conclusions. In this paper, I illustrate the use of meta-analysis by analyzing the existing data on crop responses to the practice of Conservation Agriculture (CA) in sub-Saharan Africa (SSA). In recent years a growing number of studies have been carried out in SSA comparing CA to conventional tillage (CT)-based practices. In general, the effects of CA on crop yield compared to CT in these studies are diverse, which makes it very difficult to draw general conclusions. The fact that CA is not a single component technology but is based on three principles makes that the effects on crop yield are complex. A better understanding is required of which principles and related practices, including their interactions, contribute to desired effects on crop productivity. This is all the more important, given that smallholder farmers in SSA are often facing constraints with adopting all principles of CA as a package. The meta-analysis helped in better understanding crop responses to CA and allowed identifying the agro-ecological and management conditions that favor positive crop responses to CA practices. This latter can contribute to better targeting the investments with CA development and research in SSA.