use blue instead of red litmus paper. Allow the balls of earth to 

 lie undisturbed for half an hour; then open, and if the red litmus 

 paper has turned blue no lime is needed. If it remains red, and the 

 blue litmus paper turns red, lime is needed and should be applied as 

 above directed. If neither the red nor the blue litmus paper should 

 change color during half an hour or more, then the reaction of the soil 

 is neutral and small applications of ground limestone, not to exceed 

 one ton per acre, will be sufficient. 



WHEN AND HOW GYPSUM MAY BE USED 



Gypsum may be used to good advantage on alfalfa fields to stim- 

 ulate the growth of the plants. This is especially to be remembered 

 in connection with alfalfa fields of several years' standing in which 

 "bald" spots or bare patches are found. An application of gypsum 

 in such cases, not to exceed 300 or 400 pounds to the acre, along with 

 fall disking will give striking stimulation to the plants and rejuvenate 

 the field. The reason for this is believed to be that gypsum is a 

 stimulant to the alfalfa plant itself and to the nitrogen-gathering 

 bacteria which grow in the nodules on its roots. 



If lime is very expensive, as it may be in some districts of this 

 state, gypsum, if much cheaper, may also be used as indicated above, 

 to lighten heavy soils. Applications varying from one-half ton to 

 one ton per acre may be used in such cases. 



Another use for gypsum, which is more limited, consists in apply- 

 ing it to ' ' black alkali ' ' land to neutralize or make harmless the black 

 alkali. In this respect gypsum cannot l>e replaced by lime. The 

 amounts to be used in such cases will depend on the amount of black 

 alkali present in the soil. This must be determined for those inter- 

 ested by the California Agricultural Experiment Station, which 

 should be communicated with under such circumstances. Address 

 Division of Soil Chemistry and Bacteriology, Budd Hall, Berkeley, 

 California. 



