半乾燥地域における小麦作の進展と降水量変動 : 南オーストラリア州マレーマリー地域を例として

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Exploitation of the semi-arid region of Australia began in the late 19th century. Major expansion of farm land started at the beginning of this century. The landscape covered with the dense mallee changed to wheat fields or green pasture lands. The change was very rapid and drastic.In this paper the authors examine the characteristics of marginal land for agriculture in the semi-arid region by analyzing the relationship between wheat growing and rainfall. The condition of marginal land for agriculture and the reality of wheat growing in the semi-arid region will be clarified based on the analysis of the correlation between wheat yield (bushels per acre) and winter rainfall from June to September, which coincides with the growing season for wheat. The Murray Mallee region of South Australia in the period 1907-1946, was selected as the main study area (Fig. 1). This study uses the following sources: “Statistical Register of South Australia-Production” compiled in the South Australian Parliamentary Paper, and “Report of Monthly and Yearly Rainfall, 1907-1946” collected by the Bureau of Meteorology, Australia. The 33 hundreds and stations examined are: Cadell (Morgan P. O.), Paisley (Notts Well), Waikerie (Waikerie Lands), Holder (Maggea), Moorook (Moorook), Nildottie (Swan Reach), Mantung (Caliph P. O.), Bandon (Copeville) and Mindarie (Mindarie) in County Albert, Murtho (Wilkadine), Paringa (Renmark P. O.), Gordon (Taldra P. O.), Pyap (Pyap), Bookpurnong (Loxton P. O.), Allen (Alawoona), Kekwick (Paruna) and McGorrery (Meribah P. O.) in County Alfred, Vincent (Perponda), Wilson (Borrika), McPherson (Sandalwood), Hooper (Wynarka), Marmon Jabuk (Karoonda), Sherlock (Moorlands), Roby (Coomandook), Peake (Peake), Price (Parrakie P. O.), Livingston (Kiki) and Coneybeer (Coonalpyn) in County Buccleuch, Billiatt (Gurrai P. O.), Kingsford (Karte), Bews (Lameroo P. O.), Parilla (Parilla) and Pinnaroo (Pinnaroo P. O.) in County Chandos (Figs. 2 and 3). The statistics from these hundreds and stations provided sufficient working data.Originally, wheat yield was not stable here because of the influence of variable rainfall (Fig. 4). In the semi-arid region, if rainfall is plentiful, the wheat yield increases proportionally. But if there is a scanty rainfall, mainly in winter, the wheat growing will suffer deadly damage. The characteristics of the correlation between annual wheat yield and annual winter rainfall (1907-1946) can be classified into four types: Types I-IV (Figs. 7, 8, 9 and 10). Fig. 11 shows the distribution of the four types. The data shows that hundreds included in the same type tend to be in close proximity.D. W. Goyder, the Surveyor General of South Australia, defined the extent of servere drought in 1865. This is called “Goyders Line of Rainfall”. It was a base line against which the safe and the unsafe areas for semi-arid agriculture were measured. It has a considerable validity even today. In the Murray Mallee region, “Goyders Line of Rainfall” was drawn from Swan Reach in the hundred of Nildottie to the south of Peebinga in the hundred of Peebinga near the Victorian boundary.From analysis of the four types shown in Figs. 7, 8, 9 and 10, it is clear that “Goyders Line of Rainfall” is not a fixed or static line but a boundary belt which moves dynamically within the Type II area, that is the safe and the unsafe wheat growing area. Also it can be suggested that the wheat growing conditions in the marginal land change drastically at the border, the difference being as high as 100 to 120mm of winter rainfall from June to September.

半乾燥地域における小麦作の進展と降水量変動 : 南オーストラリア州マレーマリー地域を例として

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