Cultivated area and yield dynamics of maize and soybean in South Africa: a pre- and post-GM introduction analysis (1987-2025)

Introduction South Africa has cultivated genetically modified (GM) maize and soybean commercially for more than two decades, yet long-term evidence on how cultivated area and yield evolved across the periods before and after GM introduction remains limited. Using a pre- and post-GM introduction framework, this study examines national cultivated-area and yield dynamics for maize (1987-2025) and soybean (1988-2025), using 1998 and 2001 as the predefined commercial GM introduction breakpoints, respectively. The pre-GM period refers to the historical years before commercial GM introduction, while the post-GM period covers the years from commercial introduction onward. Methods Annual commercial crop data from the Crop Estimates Committee were analysed using descriptive comparisons, Chow structural-break tests and autoregressive distributed lag (ARDL) bounds testing. Results Mean maize cultivated area declined from approximately 3.55 million ha in the pre-GM period to 2.65 million ha in the post-GM period (−25.4%), while mean yield increased from 2.28 to 4.42 t/ha (+94.1%). Mean soybean cultivated area increased from approximately 74,561 ha to 515,198 ha (+591.0%), while mean yield increased from 1.45 to 1.81 t/ha (+24.8%). The Chow test identified a significant structural break in the maize cultivated area-yield relationship at 1998 [F(2,35)=6.234, p=0.0048], but not for soybean at 2001 [F(2,34)=0.791, p=0.4615]. ARDL bounds testing supported a long-run relationship between cultivated area and yield for soybean (F=9.250, p<0.001), whereas cointegration was not supported for maize (F=3.203, p=0.226), whose selected ARDL model also showed diagnostic weaknesses. Discussion The findings reveal different patterns for the two crops. Maize yields increased despite a decline in cultivated area, while soybean experienced increases in both cultivated area and yield. However, these changes cannot be attributed solely to GM technology, as other factors, including climate, market conditions, agricultural policies and technological developments, may also have influenced the observed trends.