820 EXPEKIMENT STATION RECOED. 



periments were made on a deep soil of uniform physical and chemical com- 

 position at the experiment farm at Greenville. The irrigation water used 

 contained less than 375 parts per million of dissolved substances. 



Summarizing the results of the work, the tiuthors conclude that the maximum 

 amount of water held by the soil in question against gravity under field condi- 

 tions was about 24 per cent (on a dry basis) and the minimum amount above 

 8 per cent except that the soil of the top foot dried out to 5.64 ])er cent. 



"Irrigation was needed whenever the soil moisture fell below 12 per cent. 



"The degree to which water may be removed from the soil depends upon the 

 kind of crop grown ; and the degree of dryness at which irrigation is necessary 

 likewise depends, in a limited measure, upon the kind of ci'op. 



" Soil water was abstracted from below the depths of root penetration. 



"Water applied in irrigation, whether of large or small amount, penetrated 

 in the soil below the depth reached by augers. 8 ft. long. 



"The percentage of soil water soon after an irrigation was invariably largest 

 in the top foot, and became smaller with increasing soil depth. 



" Under given conditions of soil, crop, water, and time after irrigation, the 

 distribution of the soil Avater is always the same. This implies the operation 

 of a definite hiw governing the distribution of soil water. 



" It would seem that the water added to a soil of the Greenville type, up to 

 about 12.75 per cent on the dry basis, is held very firmly by the soil, and can 

 move only with great ditficulty. Water added above this point moves freely 

 in obedience to capillary laws. 



" It is suggested that the point below which capillary movements become 

 sluggish be called the point of lento-capillarity. 



" It would appear that water added to a soil above the point of lento-capil- 

 larity is distributed through the soil inversely with the distance from the 

 source of supply, which is the zone of wettest soil. This law of distribution 

 takes the form of the formula of the equilateral hyperbola. 



" Plants may use the soil water below the point of lento-capilhirity. but not 

 readily. 



" Plants can not use any of the true hygroscopic water. The hygroscopic 

 capacity depends largely on the amount of clay or other colloidal substances 

 found in the soil. 



" In soils of the Greenville type, under field conditions, there are several 

 critical soil water points: The maximum capillary water content, which is 

 about 24 per cent; the oi)timum water content, to a depth of 8 ft., about 18 

 per cent ; the lento-capillary point, about 12.75 per cent ; and the hygroscopic 

 capacity about 6 per cent. 



"In furrow iri-igation. the amounts of water under row and furrow are 

 unequal near the surface, but become more uniform at lower soil depths. This 

 indicates that the lateral movement of soil water increases with the depth. 



" Evaporation from bare soils is large, but may be checked by early and 

 thorough cultivation. On the Greenville farm, under average conditions on 

 cropped plats, a little more water was taken from the soil by evaporation than 

 by transpiration. The I'ate of loss of soil moisture from cropped soils depends 

 on a number of factors. 



"The removal of water from the soil by transpiration varies with the ease 

 with which j\'ater may be obtained, that is with the amount of water in the 

 soil at the beginning of an experiment. It would appear that the rate of loss 

 of soil water varies directly with the cube root of the percentage of water in the 

 soil above the point of lento-capillarity. 



"The loss of soil water increases steadily with the time after irrigation. 

 Moisture conserving methods should, therefore, be applied early. 



