24 BULLETIN" 462, U. S. DEPARTMENT OF AGRICULTURE. 



to subirrigate lands of such type near Orlando, but in every case com- 

 plete failure has followed. There have been also several attempts 

 to subirrigate the heavy clay loams of Alabama, but with most dis- 

 heartening results. The causes of failure are obvious in every case 

 when the nature of subirrigation is considered. In the attempts 

 made near Orlando the water was lost in the depths below the sur- 

 face soil and would have had to fill up all the soil above the clay 

 substratum before surface irrigation could take place. In the Ala- 

 bama installations the clay surface soils were water-logged for a dis- 

 tance of a foot or two on either side of the tile, the soil beyond being 

 perfectly dry. 



In the Sanford district, however, the distribution of the water is 

 not impeded by heavy soils. There the action of the water during 

 subirrigation has been studied carefully with the aid of a soil- 

 sampling apparatus. These tests show that the irrigation of the sur- 

 face soils is not due so much to the action of capillarity as to the 

 simple process of filling up the soils with water. Tests taken at the 

 time of irrigation show that the soil reaches the saturation point 6 

 inches under the ground surface before the surface soils are irrigated 

 sufficiently. It also is common to find free water standing in the 

 soils at 1-foot depths when the plants are in need of irrigation. 

 These tests, along with many others, show conclusively the nature 

 of subirrigation. 



It is evident that this system of irrigation requires large quanti- 

 ties of water, and consequently subirrigation under soil conditions 

 similar to those at Sanford is not an economical method where the 

 water has to be pumped. Nevertheless, it is common for the uniniti- 

 ated to regard this method with favor on account of its supposed 

 saving of water. The large quantity of water needed is no particular 

 drawback to the Sanford farmer because the nature of the water 

 supply assures him an unlimited quantity at no operating cost. 



A comparatively even ground surface, or a uniform slope, is re- 

 quired for successful subirrigation. If the ground is uneven the low 

 places will become flooded while the high knolls will not be irrigated 

 sufficiently. 



Another factor in the successful operation of a subirrigation sys- 

 tem is the correct kind of cropping. It has been stated that the San- 

 ford district depends almost entirely on garden products. These 

 crops invariably are shallow-rooted, most of the plant roots feeding 

 within 6 inches of the surface. These, being annual plants, do not 

 have an extensive root system. It has been demonstrated in the West 

 that the subirrigation of trees is a failure on account of the stopping 

 up of the tile by tree roots. This is especially true if the soil is rich 

 in plant food to the depth of the tiling. On the other hand, there are 

 records of successful subirrigation of citrus groves through tile sys- 



