THE WORK OF ROOTS 



155 



to be an injurious effect due to too much fertilizer, try 

 the effect of giving it in two or three applications a 

 few weeks apart. 



In each bed should be sown Wheat or some staple 

 crop; the watering and other conditions should be 

 alike for all the beds. The result is, of course, strictly 

 valid only for the special soil and special kind of crop 

 used, but if the soil be typical of the region and the 

 crop a staple there the result will be of great value. 

 Moreover, it will also have important general appli- 

 cations. 



The following rapid method of soil-testing, used by Prof. R. H. 

 Loughridge, of the California Experiment Station, enables one to make 

 a test in half an hour which is sufficient for all practical purposes. 1 



NITROGEN and HUMUS. To 1 part (by volume) of soil add 5 parts 

 (by volume) of 10 per cent caustic potash; this is best done in a test- 

 tube. Heat to boiling point and then set aside for five to ten minutes. 

 If the liquid is black and opaque, it indicates abundant humus and nitro- 

 gen: if the liquid allows light to pass through when held up at a 

 window, the humus and nitrogen content is low ; if the liquid is merely 

 yellow, the content of these substances is very low. The test really tells 

 us about the humus only, but, since in all except very arid regions the 

 humus content is an accurate index of the nitrogen content, the test is 

 of great value. Try this test on a soil rich in humus, such as leaf-mold 

 or soil from a grove or forest; also on some sandy soil containing little 

 humus. The color of the soil is a good indicator of the amount of humus 

 it contains; the blacker it is the more humus in it. 



PHOSPHORUS. First prepare a standard of comparison as follows: 

 Take about a pint of sand (as pure as possible) and pour on it about 

 three times its volume of dilute hydrochloric acid, made in the propor- 

 tion of one part of acid to four of water. Allow this to stand for an 



!The necessary reagents are obtainable at drug stores. 



