This law fixed a northern limit to dry farming, but it was never applied; in fact, millet cultivation spread farther and farther north, to the 10 in (250 mm) and 8 in (200 mm) isohyets
, even in the major drought that began in 1969.
25 [degrees] C intervals and mean annual precipitation isohyets
of 1-cm intervals for the region.
Yet toward the south, in the region transitional to the Brazilian shield, the mean annual isohyets
are around 2,000mm (79in) (Sioli 1985).
6[degrees]E, and between the 300 and 400 mm mean annual rainfall isohyets
with soils that are typically texture contrast (duplex) soils of sand or loams over clay (Chromosols and Sodosols) and sands over gravels (Ferric Chromosols) (Isbell 1996; Schoknecht 2002).
Perhaps the best example of zonality in savannah soils is in western Africa, where the isohyets
, the basic vegetation zones (Guinea savannah, Sudan savannah, and Sahel savannah), and the main soil types follow the same latitudinal gradient from the rainforest in the south to the desert in the north.
Climatic data were obtained from the existing meteorological stations in the area while the rainfall isohyets
for the area were determined (Pagounis, et al.
The rainfall in the study area from the Bureau of Meteorology isohyets
is between 650 mm and 600 mm.