DRAINAGE 165 



Hart (6) gives an example of a tract on which before 

 drainage the ground water stood within 2 feet of the 

 surface. A white crust of salts covered the surface and 

 nothing of value grew on the land, the only vegetation 

 being an occasional salt weed. The average salt content 

 for the first 4 feet of depth was 2.25 per cent. A drain- 

 age system was installed and in a month so much of the 

 excess water in the soil was removed, that the water- 

 table was practically down to the level of the drains. 

 The drainage water was very high in salt. By the end of 

 the month an analysis showed the salt content of the soil 

 to have been reduced to 1 per cent. The ground surface 

 was cultivated and irrigated with a limited supply of water 

 and crops were planted. These gave only fair results. 

 Meanwhile the higher temperature of summer had in- 

 creased evaporation and the average salt content for 4 

 feet was found to have increased to 1.28 per cent in spite 

 of drainage. A near-by uncultivated and unirrigated spot 

 which had been affected to some extent by the drainage 

 system showed an average salt content for the first four 

 feet of 1. 51 per cent. It was evident that drainage alone 

 would never reclaim the tract; hence, a heavy flooding 

 was given which reduced the average salt content for the 

 first 4 feet to 0.43 per cent, less than one-fifth of the origi- 

 nal content. At the same time the near-by uncultivated 

 spot showed an average salt content for the first 4 feet of 

 1.73 per cent, an increase which was caused by percolation 

 from flooding the adjacent land. 



Thousands of examples could be given to show the 

 effectiveness of drainage in reclaiming alkali lands. Many 

 failures have also been recorded. These have resulted 

 from improper methods which were decided on before all 

 conditions were studied and also from the fact that the 

 drainage system was expected to do everything. 



