Below-Average 2012/13 Corn Yields in South Africa Caused by Drought in North West and Free State Provinces
The USDA’s 2012/13 corn production forecast for South Africa was lowered from 13.5 million tons to 12.5 during the past two months, due to a drought in North West and Free State provinces during February and March, 2013. Corn yields in both provinces are expected to be below the 5-year average, with forecast yields being lowest in North West province where the drought was most severe. Although the drought was most severe in North West province, NDVI ((Normalized Difference Vegetation Index) analysis indicates the 2012/13 forecast corn yield of 2.6 tons/hectare will not be as low as yields of 1.8 tons/hectare reported for the province during the more extreme drought year of 2006/07.
South Africa’s crop conditions at the end of March are summarized in the NDVI-MODIS anomaly image shown in Figure 1, which indicates below-average crop conditions in both North West and western Free State provinces and above-average crop conditions in Mpumalanga province.
Figure 1. NDVI-MODIS Anomaly Image for March 22-29, 2013
The Foreign Agricultural Service (FAS) of the USDA estimated potential corn yields for each province in South Africa at the end of March by regressing 13-years of NDVI cropland pixels extracted from Red and Near-infrared (NIR) MODIS imagery from NASA, with 13-years of provincial corn yield data from South Africa’s Crop Estimates Committee (CEC). The corn yield forecasts from NDVI/MODIS regression analysis is updated at the end of each month for each province from January-April, with yield forecast updates occurring approximately from the pollination through the grain-filling stages. The corn crop in South Africa’s major grain belt reaches maturity in April and harvest begins several weeks to several months later, depending on how long the crop is kept in the field for drying.
The corn yield forecasts from the NDVI/MODIS regression analysis for the three largest corn-producing provinces on March 29, 2013 are presented in Table 1, along with corn yield forecasts by South Africa’s CEC released on March 26, 2013. Results from Table 1 indicate corn yield forecasts by the NDVI/MODIS regression analysis closely agreed with the CEC yield forecasts, and both agencies forecast below-average corn yields for North West and Free State provinces and above-average yields for Mpumalanga province.
Table 1. Summary of corn yield estimates for the three largest corn-producing provinces.
The summary NDVI/MODIS time series graphs for North West province are shown in Figures 2 and 3, which were obtained by extracting NDVI values from all cropland pixels within 250-meter MODIS imagery of North West province from 2000-present. In addition, the NDVI time series profiles in Figures 2 and 3 show that the 2006/07 growing period has the lowest amplitude compared to all crop years, which corresponds to the extreme drought year of 2006/07 when South Africa’s CEC estimated final corn yields at 1.8 tons/hectare for North West province.
Figure 2. Historical NDVI Time-Series Profiles Compared to Historical Corn Yields (from SAGIS)
Figure 3. Historical NDVI Time-Series Profiles for North West Province.
Figure 4 shows the 2012/13 yield-NDVI regression forecast for North West province at 2.6 tons/hectare, which is close to the 2.7 tons/hectare forecast by South Africa’s CEC. It should be noted that the yield-NDVI regression forecast methodology tends to be a conservative method which over-estimates yields for dryland agriculture during drought yields. However, irrigation corn area is increasing in South Africa North West province (see Figure 5), which should help to compensate for the over-estimated yields for dryland agriculture forecasted by the yield-NDVI regression methodology.
Figure 4. 2012/13 Corn Yield Forecast from NDVI/MODIS Regression (2000-present)
Irrigated Corn Continues to Increase in South Africa
Irrigated corn area in South Africa has more than doubled during the past 12 years. It has increased from 100,000 hectares in 2000/01 to 240,500 hectares in 2011/12, as shown in Figure 5. Irrigated corn area in South Africa is also dependent on corn price, with the 2005/06 irrigated corn area being reduced by 73,000 hectares from the previous year when corn prices were low in 2005/06. In contrast, corn prices this year have been high and USDA/FAS forecast the 2012/13 irrigated corn area to be greater than last year’s record irrigated corn area of 240,500 hectares. By assuming average irrigated corn yields at 10-tons/hectare on 250,000 hectares of irrigated corn, USDA/FAS-Washington estimates the 2012/13 irrigated corn output to be nearly 2.5 million tons, or about 20 percent of South Africa’s total corn output of 12.5 million tons.
Figure 5. Irrigated Corn Area in South Africa from 1995/96-2012/13
Center pivot irrigation systems have become very popular in South Africa, as indicated by the numerous center pivot irrigation systems shown by red circles corresponding to irrigated green vegetation in Figure 6, for the March 24, 2013 Landsat-7 image over Jan Kempdorp, South Africa. In addition, Figure 6 indicates that center pivot irrigation systems have a wide variety of diameters so that fields of many different shapes and sizes can be easily converted to center pivot irrigation systems.
Figure 7 also shows increasing amounts of irrigation within the Jan Kempdorp region, with increasing amounts of red (or green irrigated vegetation) for each Landsat image from 1973, 1998, 2008, and 2013. Figures 8-9 zoom into Figure 7, with the 1973 Landsat-1 image on the left clearly showing no center pivot irrigation systems were installed in the Jan Kempdorp region before 1973.
Figure 6. Center pivots in 2013 have a wide variety of diameters.
Figure 7. No center pivots in 1973 installed near Jan Kempdorp, South Africa.
Figure 8. No center pivots in 1973 installed near Jan Kempdorp, South Africa.
Figure 9. No center pivots in 1973 installed near Jan Kempdorp, South Africa.
Historical Landsat Images from USGS Earth Explorer
USDA/NASA’s NDVI-MODIS (with 250-meter spatial resolution) imagery archive from 2000-present
SAGIS (South African Grain Information Service)
South Africa’s Crop Estimates Committee (CEC)- Department of Agriculture, Forestry and Fisheries
NDVI/MODIS Crop Yield Analysis by GDA (Geospatial Data Analysis) Corp
Current USDA area and production estimates for grains and other agricultural commodities are available on IPAD's Agricultural Production page or at PSD Online.