230 ALKALI WATER FOR IRRIGATION 



salts in the water are retained by the soil. Large quanti- 

 ties of water applied weekly or semi-weekly kept the salts 

 moving downward continually. Means (25) states that 

 the Arabs in the Desert of Sahara raise good crops of dates, 

 deciduous fruits, and garden vegetables when irrigated 

 with water containing as high as 8000 parts per million 

 of total salts, 50 per cent of which in some cases was sodium 

 chloride. Such alkalinity, however, would not be per- 

 missible except with very resistant crops on light, sandy, 

 or well-drained soils and where great care is given to keep 

 the water from evaporating and concentrating the salts 

 at the surface. 



Without special attention to drainage, a California soil 

 irrigated with water containing 766 parts per million 

 sodium chloride, 327 parts per million sodium carbonate, 

 and 315 parts per million sulphates was proving injurious 

 to an orchard after three years (19). Impervious clay 

 soils might be injured with water too weak in alkali to 

 have any noticeable effect on well-drained ones, because 

 of the cumulative effect. 



Even in a soil with good drainage in Arizona, it was 

 found that when water containing over 1000 parts per 

 million of salts, two-thirds of which was sodium chloride, 

 was applied, 50 to 60 per cent of the salts added in the water 

 were retained by the soil or at least never appeared in the 

 seepage water of the district (8). Soils flooded by sea 

 water for 6 to 8 hours were found to contain 2000 parts 

 per million of sodium chloride in the surface soil where un- 

 flooded land contained only 100 parts per million. How- 

 ever, in a drainage experiment on the Swan Tract, Utah, 

 an alkali soil containing less than 3000 parts per million 

 of salts in the upper 4 feet of soil, when flooded with water 

 containing about 1500 parts per million of salts yielded 



