Crop Yield Forecasting

FIGURE 4.10
Coverage of digitized field crop boundaries
The digitalization of field crop boundaries has been completed for all South Africa’s nine provinces.
The advantage of using field crop boundaries as the basis for stratification is that it drastically
reduces the area that must be covered, as illustrated in Table 4.1 below. This reduction was
of 66 percent, 67 percent and 73 percent for the Free State, North West and Mpumalanga
provinces respectively.
TABLE 4.1
Advantage of using digitized field boundaries to reduce surveyed area.
Advantage of field boundaries: Survey area (ha) reduced
Province Stratification Mapped fields Reduction % Reduction
Free State 10,794,982 3,712,625 7,082,357 65.61
North West 5,776,803 1,921,927 3,854,876 66.73
Mpumalanga 4,118,568 1,103,706 3,014,862 73.20
Point frame design and random selection of sample points
The next step in the process is to randomly select the sample points (which potentially
represent cropped fields) to be surveyed in the field. The starting point for this part of the
process is the generation of a point grid of 45 m x 45 m over the total provincial area. The
grid points outside the field boundaries are then removed from the total sample population,
as these points are highly unlikely to feature any crops (see Figure 4.11 below).
Crop Yield Forecasting: Methodological and Institutional Aspects 141