726 Journal of Agricultural Research voi.vi.No. 19 



The inorganic carbon (from mineral carbonates) was determined by 

 boiling 20 gm. of soil with 50 c. c. of normal phosphoric acid under a 

 partial vacuum of about 68 cm. of mercury, absorbing the carbon dioxid 

 in N% sodium hydrate and titrating as in the case of total carbon. The 

 phosphoric acid liberates the carbon dioxid in mineral carbonates or 

 bicarbonates, but does not appear to attack appreciably the organic 

 matter. 



The humus was determined by removing the calcium from 10 gm. of 

 soil with dilute hydrochloric acid (1 per cent), washing out the chlorids, 

 extracting the soil with 500 c. c. of 4 per cent ammonia for 24 hours, and 

 measuring the intensity of the humus color in a colorimeter against a 

 standard humus solution. 



The percentage of soluble bicarbonates was determined by shaking the 

 soil with distilled water and allowing it to stand overnight. The clear 

 supernatant liquid was pipetted off the following morning into a Jena 

 flask, a few drops of phenolphthalein added, the flask covered with a 

 watch glass and the solution boiled on a hot plate; while boiling, the red 

 color was titrated out with N/io hydrochloric acid. 



The total nitrogen was determined by the modified Kjeldahl method, 

 which includes the nitrogen of nitrates. 



ORANGE SOILS 



The difficulties encountered in • correlating tree growth with soil con- 

 ditions as determined by a laboratory examination are generally recog- 

 nized. The soil environment of a tree is by no means uniform, and a 

 soil sample at best represents only the average soil condition, and wholly 

 disregards the local variations in root distribution. In the present 

 investigation the correlation between mottling and soil composition is 

 further complicated by the fact that an orange or lemon tree is, generally 

 speaking, slow in response to fertilizer stimuli under the method of 

 orchard management prevailing in the area studied. An application of 

 barnyard manure, for example, even when thoroughly worked into the 

 soil, does not cause tree response until some time after the manure has 

 decomposed. Under such circumstances a soil sample may not repre- 

 sent the soil conditions responsible for the condition of the trees at the 

 time of sampling 



