44 Effective Farming 



The addition of humus-forming materials, such as farm manure, 

 green-manure, or muck, increases the capacity of a soil, espe- 

 cially if it is sandy, to retain water. Humus has the power of 

 absorbing and retaining water and when added to soil increases 

 the water-content. Humus also reduces the size of many of 

 the pore spaces, and, in the case of a sandy soil, results in a 

 finer soil that is more retentive of water. 



22. Irrigation. In arid and semi-arid regions irrigation, or 

 the artificial supplying of water to soil, is necessary for crop 

 production. In these regions large irrigation systems that 

 supply vast areas are installed and water rights are sold with 

 the property, for without the water the land is practically worth- 

 less for crop production. 



In humid regions irrigation is sometimes practicable, for 

 in certain sections the rainfall is so distributed that periods of 

 drought are likely to occur during the growing season with a 

 consequent complete or partial loss of the crop. Vegetable- 

 gardens, nurseries, small-fruit plantations, and greenhouses 

 are often irrigated, but for less intensive farming the supplying 

 of water artificially is not often profitable. 



In general, four methods are in use for distributing water in 

 irrigation. These are overhead irrigation, sub-irrigation, flood- 

 ing, and furrow irrigation. 



Overhead irrigation. In humid regions overhead irrigation 

 is used largely for watering market-garden crops, fruit crops, 

 and in greenhouses. A system of overhead pipes is arranged in 

 parallel lines across the area to be irrigated. These pipes, 

 which are fitted with small holes at regular intervals, are con- 

 nected with a water-supply system and water is delivered to 

 them under pressure. The holes in the pipes are fitted with 

 small nozzles that cause the water passing through them to 

 break into a spray, thus preventing the packing of the soil 

 that would result were the water to reach the ground as a stream. 

 Fig. 17 shows an irrigated garden of the Irrigated Farms Com- 

 pany near Trenton, New Jersey. 



