Agroclimatic variability in the Free State province: a case study in the Setsoto Municipality.

Abstract

This study investigated the impacts of agroclimatic variability; minimum and maximum temperatures and rainfall on maize yield in the Setsoto municipality in the central eastern part of the Free State province of South Africa from 1985 to 2016. This study focused on the Setsoto municipality, because it has been shown that the variability and uncertainty in temperature and rainfall across weather stations, even those close to each other is high. This variability may be impacting maize yield. The daily minimum and maximum temperatures and the rainfall were obtained from the Agricultural Research Council (ARC) and the South African Weather Service (SAWS) for a period from 1985 – 2016. The annual maize yield data was obtained from the Department of Agriculture Forestry and Fisheries (DAFF).

In this study the monthly as well as the growing period (Apr -Oct) minimum and maximum temperatures for the period between 1985 and 2016 varied across the four target stations (Clocolan, Senekal, Marquard and Ficksburg) of the Setsoto municipality. In Clocolan, the monthly minimum temperature and the entire growing period significantly declined by 0.2 to 0.12 °C year-1. A similar trend was also observed in Marquard for some of the months. The maximum temperature trend increased significantly across all the stations by 0.04 - 0.05 °C year1 during the growing period, while on a monthly basis it increased between 0.018 - 0.12 °C year-1 mostly in October, November and March (P < 0.005). The temperature effects were most influential in the months of November and February when leaf initiation and kernel filling occur, respectively. The results showed there was no significant change in rainfall during the growing period across the municipality. Neither the onset nor the cessation of the rains changed significantly over the study period. The duration of the rainfall in all the four stations of the municipality used in this study was sufficient for maize production. Nevertheless, the maize yields of these stations were low, ranging from 1.96 – 2.89 tons ha-1. Although, rainfall does show a strong positive correlation with yield, it is also affected by number of environmental factors among which are the rainfall distribution through the season, minimum and maximum temperatures, soil nutrients as well as other edaphic factors. One unit of rainfall (mm) can increase the maize yield by 0.005 and 0.015 t ha-1year-1

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The overall variation in maize production in Setsoto municipality was due to the variable agroclimatic anomalies, the minimum and maximum temperatures as well as the rainfall ranged from 13.5-15.2%, 21.4-43.2% and 17-47.3% respectively over the period of this study. The increasing minimum and maximum temperatures at all of the stations showed that: where the minimum temperature is currently too low for optimal growth, an increase in these temperatures will increase yield; and the overall increase in both the minimum and maximum temperatures over time will have a negative impact on crop yield, but the magnitude of the effect is dependent on when exactly the increases during the growing season occurs. There are some concerns that as temperatures and rainfall variability increase the area will become marginal for maize production. Yield is not controlled only by agroclimatic variables, but together with a combination of a number of farming practices including area of land planted, fertilizer and pesticide usage etc.