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Production
Estimates and Crop Assessment Division |
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Production
Estimates and Crop Assessment Division |
October 13, 2004
USDA's October estimate for South Africa's 2003/04 corn production, for both developing and commercial agricultural sectors, is 8.93 million tons, up 234,000 tons from last month but down 741,000 from last year. USDA's October corn production estimate is consistent with final corn estimates by South Africa’s Crop Estimates Committee (CEC) released on September 20th. Production estimates by the CEC are based on corn deliveries to grain bins, but FAS' Pretoria office recently reported that grain bin deliveries from March to August 2004 were 8.76 million tons and the CEC may have underestimated the 2003/04 crop by 500,000 tons. USDA's area estimate is 3.2 million hectares, or 200,000 hectares above CEC's area estimate of 3.0 million. This year's area estimates by CEC were the lowest since the 1930’s and these low area estimates were not adjusted upwards later in the season which gave a high national yield of 2.97 tons/hectare. In contrast, USDA's yield is 2.79 tons/hectare or slightly above the 5-year average yield of 2.64.
The time series graph (shown below) for commercial corn production, area, and yield indicates that CEC did not adjust its area estimate later in the season, although CEC area estimates were adjusted upwards later in the season for the past five years. The CEC first production estimate also assumed a yield below the 5-year average, which is not recommended for early season estimates because rainfall is highly variable in the region.
In addition, final CEC yield estimates for 2003/04 were high when irrigated area was low from low reservoir levels caused by dry winter and summer seasons in 2003. In summary, CEC yields appear high because area was under-estimated at the beginning of the season; these low area estimates were not adjusted upward later in the season as done in previous years, and irrigated area was also low when compared to previous years.
FAS/PECAD, in cooperation with NASA-Goddard and University of Maryland, recently developed a powerful tool for monitoring crop yields at the provincial level by using MODIS (Moderate Resolution Imaging Spectroradiometer) data onboard the Terra and Aqua satellites from January 2001 to present. This NDVI/MODIS tool can extract NDVI values for 250-meter resolution pixels classified as croplands within each administrative unit (or polygon). The NDVI/MODIS tool was used to plot NDVI time series curves for the three major corn-producing provinces of South Africa: Free State, Mpumalanga, and Northwest. Results were compared to CEC provincial yield data for the past three years.
The NDVI/MODIS results indicate that CEC probably under-estimated area and over-estimated yields for Mpumalanga and Northwest provinces during the 2003/04 season. For the Free State province, the CEC yield estimates are close to the 3-year average as indicated by the MODIS/NDVI time series graph. However, for Mpumalanga and Northwest provinces, CEC yield estimates were above the 2001/02 bumper year although NDVI/MODIS data indicate slightly-above average yields and below 2001/02 bumper yields. It is important to note these discrepancies because similar errors could be transferred to next year’s crop estimates if the 2003/04 season is used as a baseline year.
Planting for the 2004/05 corn crop will begin this month; the CEC currently estimates planted area for commercial corn at 2,854,000 hectares, or slightly over 200,000 hectares from last year. CEC has under-estimated planted area early in the season for the past five years due to its farmer survey methodology. These initial area estimates for 2004/05 may be adjusted later in the season by 100,000 hectares or more.
FAS-Pretoria
GAIN Report (10/6/2004)
FAS/PECAD MODIS
Project with NASA and University of Maryland
NDVI/MODIS 250-meter Interactive Tool (for Crop Yield
Analysis at Provincial-Level)
Corn Yields Improve for South Africa
South Africa: Planted Corn at Historic Lows
South Africa: Crop Tour Summary
South Africa Grain Bins
Low Corn Area Estimates at Start of Season for Past
5-Years
Irrigated Corn
Increases in South AfricaCrop
Explorer for Southern Africa
