84 THK RAISIN INDUSTRY. 



the land. Whenever such subirrigation exists, the water level will be 

 found higher in the winter than in the summer, and drainage should 

 accompany subirrigation in nearly every instance. A subirrigation 

 like the above exists in Denia and other of the Spanish districts. 

 Subirrigation may be also caused by either impervious subsoils, such 

 as hardpaii and clay, or by spongy subsoils, which keep the water like 

 a sponge. Such is the case to a limited extent in parts of San Ber- 

 nardino county. At Redlands, for instance, much less irrigation is 

 now used than when the vines were first planted, and this fact is 

 attributed to a spongy subsoil peculiarly retentive of water. A similar 

 subirrigation exists in the Mussel Slough country, where the water 

 rapidly fills the land and keeps it moist throughout the summer. The 

 phenomenal moisture of the El Cajon land is probably also produced 

 by some kind of subirrigation, either on impervious or through reten- 

 tive strata; the waste water from the surrounding hills no doubt 

 supplies much of the water appearing in the lower lands of the valley. 

 Other valleys close by do not show this moisture, the underlying strata 

 probably making subirrigation impossible with the present amount of 

 rainfall. 



Seepage. Seepage is the quality of the soil to attract moisture and 

 retain it. Seepage soils attract the water from a ditch run through 

 the land, the water spreading all through the soil towards all sides 

 instead of sinking only vertically down. There is a distinct difference 

 between such seepage soils and those that do not seep, although there 

 is a gradation in the degree of the seepage, some soils seeping more 

 than others. Thus the Fresno soil, or the soils on the Fresno plains, 

 especially the red and sandy soils, do not seep or percolate. Vines 

 planted on the sides of the ditches, or a foot or two from their banks, 

 will die and dry up if not specially irrigated by bringing water to 

 their very roots. Other soils, especially the river-bottom soils or the 

 alluvial soils, seep or percolate in a great or less degree. They act 

 like a sponge, attract water and give it away slowly, and the soil will 

 be found wet for long distances from the ditch. This seepage capacity 

 of the soil is partly caused by an abundance of humus or vegetable 

 matter. The seepage capacity of the soil greatly increases by admix- 

 tures of green vegetable matters through the plowing under of green 

 crops, such as alfalfa, peas, beans, grain, etc. The value of seepage 

 soils is seen especially where some uneven ground is scraped off and 

 the top soil removed to low places. Such ground often becomes use- 

 less for years afterwards, especially if the quantity of humus in the 

 lower soils is small. Frequent irrigations will not serve to keep such 

 soils moist, as the water sinks rapidly down, leaving the poor top soil 

 dry. Vines planted in such places never -do well, and even heavy 

 manuring will not suffice to bring on a strong, healthy growth. Such 

 humus-wanting soils must be treated with green crops, as stated above, 

 in order to become fertile and moist. Thus seepage and subirrigation 

 are often confounded. The former is caused by the retentive and 

 communicative quality of the soil, while the latter is caused by the 

 natural or artificial distribution of the underground water. 



Subirrigation and seepage combined make the most perfect irrigation 

 for a raisin vineyard, with advantages that can in no other way be 



