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in dry-land farming the most important problem is naturally the 

 amount and distribution of the rainfall. The rain falling in the course 

 of a year is usually measured in the form of inches. This amount ranges 

 all the way from nothing or a mere fraction of an inch, as in the Andes 

 and the great African and Asian deserts, to as much as 600 inches, or 50 

 feet, at Cherapundji, in Eastern India. In studying a rainfall map of 

 the world, it will be seen that a large portion of the earth's surface is 

 arid. This term is commonly meant to imply an annual average of less 

 than 20 inches. The arid region thus denned would include, in the 

 United States, most of thejcountry lying west of a line drawn through 

 North Dakota and Texas, extending north-west into Canada and south- 

 wards into Mexico ; while in South Africa it would be found in the 

 Kalahari Desert, the Karoo, and some portions of the Transvaal. 



Dr. Briggs, of the National Department of Agriculture, Washington, 

 was the first to call attention to the enormous importance of evaporation 

 in relation to dry-farming. And this is a matter of equal, if not greater, 

 importance to the South African farmer in our land of hot suns, bare veld, 

 and dry, sweeping winds. To watch a terrific thunderstorm, to see rivers 

 of water pouring over the land, and a few hours later to walk over perfectly 

 dry ground is a phenomenon familiar to every farmer. This appalling 

 waste is mainly due to hard impenetrable soil ; in a word, to surface run 

 off, and, secondly, to the sucking power of a summer sun. 



Evaporation, therefore, is a factor which should not be ignored in 

 passing judgment on the agricultural productiveness of any region. By 

 the term evaporation is meant the number of inches of water which 

 vaporises or evaporates from a clean water surface in a freely exposed 

 open tank during a given period. Thus the annual evaporation is the 

 total number of inches of water which evaporates during the year, just 

 as the precipitation is measured by the total number of inches of water 

 falling into a tank, as rain, sleet, or snow during the year. 



Evaporation depends upon the temperature of the evaporating surface, 

 the dryness of the air, and the velocity of the wind. The hotter the day, 

 the greater the evaporation ; the drier the day, the greater the evapora- 

 tion ; the harder the wind blows, the greater the evaporation — a ceaseless 

 sucking up of moisture. The amount of evaporation from an open tank 

 of water is thus a measure of the evaporation of that locality A series 

 oi evaporation determinations has been made recently by the United 

 States Department of Agriculture at various points throughout the West 

 during the months of spring and summer. These tests were made by 

 means of a freely exposed tank set in the soil, and some remarkable results 

 were obtained. At North Dakota, with a summer rainfall of 13 inches, 

 the evaporation from the tank was 30 inches, and at Amarillo, Texas, during 

 the same period, with a summer rainfall of 13 inches, the evaporation was 

 54 inches. Summarising these experiments, Briggs says : u In other words, 

 with the same rainfall in North Dakota and at Amarillo during the growing 

 season, the man at Amarillo would be working under conditions which are 

 practically twice as severe as those in. North Dakota," The prospective 

 dry-land farmer must therefore realise that the annual rainfall is not the 

 only factor to be considered in selecting his homestead, since the greater 

 the evaporation in any given locality, the harder will it be for him to 

 conserve enough moisture to produce his crops. 



How then can moisture be conserved ? The answer is : by deep 

 ploughing, constant cultivation, and the prevention of evaporation. 

 Ploughing is the most important operation in dry-farming, and upon it 

 will mainly depend the success or failure of the crop. The dry-land 



