Does minimum tillage with planting basins or ripping raise maize yields? Meso-panel data evidence from Zambia

Despite nearly two decades of minimum tillage (MT) promotion in Zambia, there is limited empirical evidence on its effect on maize yields under typical smallholder conditions. We use nationally representative survey data from nearly 48,000 smallholder maize plots for the period 2008-2011 to estimate the maize yield effects of the primary MT strategies promoted in Zambia: planting basins and ripping. The estimation approach applies pooled ordinary least squares-correlated random effects to control for time invariant unobserved heterogeneity at the enumeration area level. All else equal, yields on plots tilled with ripping are significantly higher than on conventionally plowed plots if tillage is done before rather than during the rains. The gains average 577 kg/ha nation-wide and 821 kg/ha in agro-ecological zones 1 and 2a (the two zones most suitable for conservation agriculture). Planting basins also have a positive effect on yields, increasing maize yields by 191 kg/ha on average relative to conventional hand-hoe tillage when tillage is done before the onset of the rains. These results suggest that MT with ripping and basin tillage only substantially raises smallholder maize yields relative to conventional tillage when combined with early land preparation.