Wheat Yield Potential and Yield Gaps in South Africa.

Wheat (Triticum aestivum L.) production in South Africa declined sharply over the past decade because of rising input costs and low global wheat prices, among other challenges. In the present research article, the possibility of improving wheat yields in production systems of South Africa was explored through analysing average farmer yields (Y_a), yield potential (Y_p,  - or water limited yield potential [Y_w] in the case of dryland wheat) and yield gaps (Y_p or Y_w – Y_a). Wheat yield data was obtained from farmer-representative yield trials that were conducted continuously over 15 years from 2000 to 2014 across the major production areas of South Africa, namely the summer rainfall area (SRA), the winter rainfall area (WRA) and the irrigation area (IA). Average yields for dryland wheat in the SRA ranged from 1.62 ± 0.046 to 3.61 ± 0.068 t ha^-1 and were significantly higher (p<0.001) for later plantings than early plantings. For the WRA, dryland wheat Y_a ranged from 3.48 ± 0.072 to 3.85 ± 0.15 t ha^-1, and it was significantly higher (p<0.001) for conventional tillage (3.79 t ha^-1) than reduced tillage (3.59 t ha^-1). However, Y_w was higher for reduced tillage (5.67 t ha^-1) than conventional tillage (5.32 t ha^-1). Irrigated wheat Y_a ranged from 6.64 ± 0.15 to 8.32 ± 0.10 t ha^-1 and were highest among precision farmers. The exploitable yield gaps, hence potential to improve farmer yields were as follows: SRA (0.46 – 1.48 t ha^-1), WRA (0.38 - 1.04 t ha^-1) and IA (0.44 – 1.41 t ha^-1). Yield gaps were positively related to the Y_p. Dryland and irrigated wheat could be increased by 10 – 48% and 7 – 17% through closing exploitable yield gaps in various production systems, respectively. Refinements in farmer planting date decision and tillage practices are important considerations for closing the wheat yield gaps.