AFRICA
6.5 Conducive and Non-Conducive Growing Conditions
6.5.2 Distribution Patterns of Conducive and Non-Conducive Sugarcane Growth Conditions
Maps of conducive and non-conducive growing conditions were produced for the months of January and June, in order to represent summer and winter conditions, respectively, and for the entire year. In Figure 6.35, showing conducive cane growth units for the month of January, the majority of conducive growing conditions are found in the eastern half of the country, with values ranging from approximately 60 units to in excess of 240 units. Regions showing the greatest potential for sugarcane growth, according to these criteria, include the central and southern coast areas of KwaZulu-Natal, central Swaziland, Mpumalanga and the central Limpopo provinces. The distribution patterns shown in this map may be attributed to the fact that soil water contents in these areas, at this time of year, are largely in excess of 50% PAW, therefore allowing for the accumulation of heat units. The opposite is true for the western half of the country, where temperature conditions would be conducive, but the lack of soil water would result in sub-optimal growing conditions for sugarcane.
18°E 24°E 30°E 32°S
25°S
CONDUCIVE GROWTH UNITS January
0 - 60 60 - 120 120 - 180 180 - 240 > 240 Mean number of conducive growth units
Base
temperature: 10ºC SMC > 50 % PAW
Figure 6.35 Mean number of conducive growth units for the month of January
The distribution patterns shown in Figure 6.36 are vastly different to those for January. In June the majority of conducive growth units is limited to the coastal areas, with the Western Cape indicating the largest area in which conditions are favourable for growth. The number of conducive growth units for these regions range between 25 and 75, which is significantly lower to those of January. For the winter period, soil water contents and temperature are both too low for optimal sugarcane growth in the inland regions of South Africa, resulting in the low number of optimal heat unit accumulations. Parts of the Eastern Cape may have sufficient soil water content (cf. Figures 6.3 and 6.11), but owing to the low winter temperatures there is only a low accumulation of optimal growth heat units (cf. Figures 4.1 to 4.8). When comparing the distribution patterns shown in Figure 6.35 with those in Figure 6.36, it may be seen that, although some areas in the summer months may show optimal growing conditions for sugarcane, it is not possible to grow sugarcane in these areas owing to lack of optimal growing conditions in the winter.
18°E 24°E 30°E 32°S
25°S
CONDUCIVE GROWTH UNITS June
0 - 25 25 - 50 50 - 75 75 - 100 > 100 Mean number of conducive growth units
Base
temperature: 10ºC SMC > 50 % PAW
Figure 6.36 Mean number of conducive growth units for the month of June
Figure 6.37 shows the distribution patterns of non-optimal heat units for the month of January. These range from less than 125 units in areas of the eastern parts of South Africa to between 500 and 625 heat units in the central and northern regions of South Africa. The relatively high numbers of heat units found in the central and northern parts of South Africa may be attributed to the high temperatures in combination with relatively low rainfall amounts during this time of the year. Figure 6.37 confirms the results shown in Figure 6.35, in that during summer months, the northern parts of the Eastern Cape, KwaZulu-Natal, central Swaziland, Mpumalanga and central Limpopo show conditions that are conducive to sugarcane growth. The patterns shown in Figure 6.38 of non-conducive heat units for the month of June show a very different pattern to those shown in Figure 6.37. The majority of non-conducive heat units are concentrated around the coastal and northeastern regions of southern Africa. The total number of accumulated heat units varies from fewer than 50 units in the central and southeastern parts of southern Africa, to in excess of 200 units in the northeastern regions of southern Africa. The relative lack in the number of heat units, especially in the central areas of southern Africa, may be attributed to the low temperatures during this time of the year, which results in the reduced number of accumulated units.
18°E 24°E 30°E 32°S
25°S
NON-CONDUCIVE GROWTH UNITS January
0 - 125 125 - 250 250 - 375 375 - 500 > 500 Mean number of non-conducive growth units
Base
temperature: 10ºC SMC < 50 % PAW
Figure 6.37 Mean number of non-conducive growth units for the month of January
18°E 24°E 30°E
32°S 25°S
NON-CONDUCIVE GROWTH UNITS June
0 - 50 50 - 100 100 - 150 150 - 200 > 200 Mean number of non-conducive growth units
Base
temperature: 10ºC SMC < 50 % PAW
Figure 6.38 Mean number of non-conducive growth units for the month of June
Distribution patterns of mean annual conducive and non-conducive growth units for southern Africa are shown in Figures 6.39 and 6.40 respectively. In Figure 6.39, the majority of conducive growth units are found in the eastern half of southern Africa. Regions showing the
greatest potential for sugarcane growth include the northeatern parts of the Eastern Cape, coastal and midland regions of KwaZulu-Natal, central Swaziland, Mpumalanga and parts of Limpopo province, where values ranged between 1000 and 1750 growth units. These distribution patterns may be attributed to higher incidences of moist soil conditions as a result of higher magnitudes of mean annual precipitation, as depicted by Schulze and Lynch (2007).
The mean annual non-conducive growth units, shown in Figure 6.40, depict the coastal, northern and north-eastern parts of southern Africa as having the highest numbers of non- conducive growth units, with numbers ranging from ~ 1500 units to > 3750 units. The high number of non-conducive growth units is evidence of the generally hot and arid nature of much of southern Africa. The distribution patterns of non-conducive growth units follow very closely to the distribution patterns of mean annual temperature as depicted by Schulze and Maharaj (2007a), which shows the distribution of non-conducive growth units is largely affected by temperature through its influence on heat units.
18°E 24°E 30°E
32°S 25°S
CONDUCIVE GROWTH UNITS Annual
0 - 250 250 - 500 500 - 750 750 - 1000 1000 - 1250 1250 - 1500 1500 - 1750 > 1750 Mean annual number of conducive growth units
Base
temperature: 10ºC SMC > 50 % PAW
Figure 6.39 Mean annual number of conducive growth units for southern Africa
18°E 24°E 30°E 32°S
25°S
NON-CONDUCIVE GROWTH UNITS Annual
0 - 750 750 - 1500 1500 - 2250 2250 - 3000 3000 - 3750 > 3750 Mean annual number of non-conducive growth units
Base
temperature: 10ºC SMC < 50 % PAW
Figure 6.40 Mean annual number of non-conducive growth units for southern Africa