Crop rotations and residue management in conservation agriculture

Abstract

Yield increases and sustainability of conservation agriculture (CA) systems largely depend on systematic crop rotations and in situ crop harvest residue management coupled with adequate crop nutrition. In this chapter, the beneficial effects of crop residue management and crop rotations on maize (Zea mays L.) grain yield in CA systems under rainfed conditions are explained through a meta-analysis. The effects of crop residue management are most beneficial under rainfed conditions as rainfall distribution is often erratic and seasonal dry spells common. The meta-analysis was based on the weighted mean difference (WMD) effect size using the random effects model. Yield advantages of CA systems over conventional tillage systems were only significant when in rotation, under low rainfall conditions and with large N fertiliser inputs. The WMD for CA with continuous maize ranged from − 1.32 to 1.27 with a mean of − 0.03 t ha−1, and when rotation was included the WMD ranged from − 0.34 to 1.92 with a mean of 0.64 t ha−1. Mulch retention under low rainfall (< 600 mm) had a WMD between −0.2 and 1.0 with a mean of 0.4 t ha−1 while high rainfall (> 1000 mm per season) reduced the yield advantage with the WMD ranging from − 1.2 to 0.02 with a mean of − 0.59 t ha−1. CA is likely to have the largest impact in low-rainfall environments where increased infiltration of rainfall and reduced evaporative losses are achieved by retaining crop residues. However, it is in these areas that achieving sufficient crop residues is a challenge, particularly in mixed crop–livestock systems where crop residues are needed for livestock feed in the dry season. The results suggest that CA needs to be targeted and adapted to specific biophysical as well as socioeconomic circumstances of farmers for improved impact. The ability of farmers to purchase fertiliser inputs, achieve sufficient biomass production as well as produce alternative feed will allow them to practise CA and possibly achieve large yields.