816 EXPERIMENT STATION RECORD. 



maintain a good appearance in tlie trees but not to produce new growth : the 

 application of irrigation water caused increased growth. 



" The unobstructed movement of water in loam soils is downward, with 

 great irregularity in rate of progress and in the amount of water retained at 

 various depths. The water beneath the surface does not move from the furrows 

 toward the trees for more than 2 ft., and at a depth below 2 ft. the wet area 

 is usually rapidly contracted to a cone shape. The soils in the tree rows, 

 therefore, fail to receive any of the irrigation water, and the dry space increases 

 in width and extent downward; the tree* roots, which usually are confined to 

 the upper 3 ft., are thus only partially supplied with needed moisture. 



" The relative proportion of dry soil to that wetted by irrigation across 16 

 furrows and 4 tree rows in the sandy loam soil, was as 2 to 3 in a depth of 

 5 ft. As seen in the profiles, the proportions are as follows, taking the dry 

 soil as the unit : Surface foot, 1 to 3.4 ; second foot, 1 to 4.3 : third foot, 1 to 

 2.3 : fourth foot. 1 to O.S : fifth foot, 1 to 0.4 : and sixth foot, 1 to 0.1. 



" The depth reached by the percolation of irrigation water deitends on the 

 nature of the soils and length of time of flow ; in the unobstructed loose soil 

 it was 26 ft. near the head ditch, 4 ft. In the middle, and about the same 

 at 30 ft. from the end, and many feet where the excess was received. In the 

 compact, semiimpervious soil it reached a depth of 4 ft., while in the imper- 

 vious hardpan soil the depth was but little more than 12 in. even after 3 days' 

 application. 



" The amount of water held by the soil when the downward movement ceased 

 was always gi-eatest in the upper 2 ft. and diminished in percentage to the 

 bottom. [The general averages of 9 furrows were] 9.95 per cent in the first 

 foot, 11.19 in the second, 9.14 in the thii-d, and 8.27 per cent in the fourth foot. 



" The presence of an impervious hardpan near the surface causes sidewise 

 seepage of the water, a greater wetting of the surface, and consequent in- 

 creased Idss by evaporation and by accumulation and run-off at the lower end 

 of the furrows. 



" Shallow irrigation furrows do not give as good results as deep ones; they 

 allow a large part of the water to rise by capillarity to the surface on either 

 side and thence to escape into the air by evaporation, while deep furrows 

 enable the soil to receive and retain nearly all of the water applied. The 

 furrows in [the principal orchard experimented with] had an average depth 

 of 3 or 4 in. and from these the lateral seepage was so great as to wet about 

 85 per cent of the space between the tree rows. During the 3 days of irri- 

 gation in which these soils were being kept wet the rate of evaporation was 

 very high. After this the soil gradually dried out and the loss diminished. 



" On loose sandy loams water percolates with such rapidity near the head 

 ditch that a great part is lost by passing far below the roots and possibly into 

 sand and gravel strata, through which it fiows away. Thus on [one] orchard 

 the depth of percolation was 26 ft. at a distance of 30 ft. fi'om the ditch. 



" It is extremely doubtful [whether] water at a depth of more than 5 ft. below 

 the root systems will be of any benefit to the trees in times when needed, for the 

 capillary rise is extremely slow, and especially so if the temperature of the soil 

 be low. . . . 



" In orchards with shallow mulches it was observed that the amount of water 

 in the soil 6 weeks after irrigation was about the same as just previous to the 

 application of water. . . . 



" Percolation is influenced by the time that water is allowed to remain in the 

 furrow. The water should be made to reach the end of the furrow as soon as 

 possible, and then the flow so regulated that the whole line may receive prae- 



U 



