58 CALIFORNIA VEGETABLES 



ment, and the observing man will allow the plants to tell him by 

 their vigor and speed of growth how the supply suits them. 



It is possible to tell how much water will bring a certain depth 

 of soil into the best condition for growth and working. With this 

 knowledge the gardener can more rationally follow the results of 

 his observation of the plants themselves. The following are the 

 conclusions of the late Professor F. H. King from very careful 

 investigation and experiment: 



The maximum capacity of upland field soils for water ranges from about 

 eighteen per cent of their dry weight for the light sandy types to about thirty 

 per cent for the heavy clayey varieties, while the amounts of water these 

 soils should contain in order that plants may thrive in them best is from 

 twelve to fourteen per cent for the former and from eighteen to twenty per 

 cent for the latter. The growth of plants will be seriously checked in sandy 

 soils when the water content falls below eight per cent, and in heavy, clayey 

 types when it falls below fourteen per cent of the dry weight of the soil. 



The dry weight of a light sandy soil and subsoil will average about one 

 hundred and five pounds per cubic foot, and the heavy clayey type about 

 eighty pounds per cubic foot. Hence the maximum amount of water per 

 cubic foot of soil would be about twenty-four pounds for the clay and eighteen 

 and nine-tenths pounds for the sand. This being true, four and six-tenths 

 inches of water on the level would completely saturate the surface foot of 

 heavy clay soil, were it entirely dry to begin with, while three and six-tenths 

 inches would place the sandy soil in a similar condition. 



But since water should be applied as soon as the water content of the 

 sandy soil falls to eight per cent and that of the clayey soil to fourteen per 

 cent, it follows that under these conditions ten and five-tenths pounds of 

 water, or two inches, is the maximum amount which would be needed to 

 fill the surface foot of sandy soil and twelve and eight-tenths pounds, or two 

 and forty-six one-hundredths inches, is enough to fill the surface foot of 

 clay soil. 



If we consider the second foot of soil to have been dried out to a cor- 

 responding extent, and that it is desirable to saturate this with water also, 

 then the amounts just stated would need to be doubled, four inches being 

 demanded for the sandy soil and four and ninety-two one-hundredths inches 

 for the clayey soil. It is quite certain, however, that such an application of 

 water to a field at one time would result in the percolation of a considerable 

 amount of this water below the depth of root action, and hence in a con- 

 siderable loss of it unless a large crop were growing upon the land at the 

 time. It appears, therefore, that the amounts of water which may be applied 

 to a field at one time will lie between two and five inches in depth over its 

 whole surface. 



How often this watering may need to be repeated it is not possible to 

 state in anything like definite terms, but practical experience shows that as 

 a rough average the intervals between watering where maximum yields are 

 sought cannot much exceed seven to fourteen days, the time being shortest 

 when the crop is making its most vigorous growth. 



This account is useful as showing how much the soil may be 

 expected to hold, consequently the maximum to be considered in 

 application. The times of repetition naturally have to be indefinite 

 because rates of evaporation and leaching are so variable. If the 

 reader should get the idea from these calculations that he ought to 

 have a generous water supply for the best summer growth of vege- 

 tables, he will start right at least. He will soon learn how to use 

 the water to the best advantage. 



