Frost and its Implications on Maize Production in the Free State Province of South Africa

Frost in the Free State is considered as one of the main hazards that have negative impact on crops. In this study, spatial variability on the onset of frost, cessation of frost and duration of frost will be investigated with reference to the maize growing season. Research on the timing of the frost and its duration is important for sustainability of maize production in the province. The frost indices are determined for varying risk levels (20%, 50% and 80% exceeding and non-exceeding probabilities). The onset of frost for all the thresholds is earlier over the northern, eastern and far southeastern parts of the Free State while the first frost dates are later over the western and southwestern parts. The northern and eastern parts are also marked by late cessation of frost, giving a shorter frost-free period (220-240 days at medium frost severity). The western and southwestern areas mostly have earlier cessation of frost, resulting in a relatively long frost-free period (241-300 days at medium frost severity level). Cessation of frost occurring later than normal over the Free State can impact negatively on the maize crop if planted in October and early November, especially over the highlands. Productivity of the crops can also be hampered by earlier than normal onset of frost that affects maize at silking and grain-filling stages.