Impact of preceding crop sequences on wheat growth and development under conservation agriculture in the eastern Free State, South Africa

Conservation agriculture (CA) is advocated to promote sustainable cropping. Little is known about the impact of preceding crop sequences on the growth and development of dryland wheat under CA in the eastern Free State Province of South Africa. In a criss-cross experimental design, the response of wheat planted after 25 summer and 25 winter crop sequences was evaluated. Biomass yield was a more reliable indicator than grain yield as a consequence of water and nitrogen stress in the reproductive phase as indicated by harvest index, precipitation use efficiency and nitrogen agronomic efficiency. The five best sequences that favoured wheat biomass yields were, in decreasing order: grain sorghum × maize, sunflower × dry bean, sunflower × maize, soybean × soybean, and maize × maize for summer crops (7.1–7.8 t ha−1); and fallow × vetch, fallow × wheat, fallow × fallow, vetch × fodder oat, and wheat × oat for winter crops (6.5–7.4 t ha−1). Of the grading parameters, only protein content was influenced significantly by the winter crop sequences. A single 3-year cycle comprising wheat after two seasons with preceding crop sequences was insufficient to test abiotic stress factors thoroughly to establish with certainty the best crop sequences for dryland wheat production.