1914] Loughridge: Humus and Nitrogen in California Soil Columns 177 



for the upper two feet, as it was not then known that the humus 

 reached to a greater depth than three feet. In the rej)ort for 

 1904 the first analysis is given of a soil with humus to a depth 

 of twelve feet. 



During these years the call from farmers for information 

 regarding the needs of their soils was very great, and thousands 

 of soils were sent in for examination. These did not require an 

 accurate and full analysis in every case, and were subjected to 

 cursory tests* by which approximate determinations could be 

 reached very quickly for phosphoric acid, lime, and humus. The 

 results were graded into "poor" for less than 0.7 per cent; 

 "fair" for 0.7 to 1.0 per cent; and "good" when the percentage 

 was above 1.0, and only the surface soils were examined. From 

 1893 to 1908 there were made humus tests on nearly fifteen 

 hundred soils distributed among the following agricultural 

 regions ; in this table are given the percentages of soils whose 

 humus belonged to the several grades. 



Table 2. — Humus in Soils of the Agricultural Regions; Quick Method 



No. of soils Percentage of soils having 



examined Good Fair Poor 



Regions for humus humus humus humus 



Sacramento Valley 211 55 18 27 



San Joaquin Valley 434 24 24 52 



Foothills of Sierra Nevada 66 59 12 29 



Coast Range valleys 398 64 19 17 



Southern California 347 43 23 34 



Average 1,456 46 21 33 



It will be seen from the above that more than one-half of the 

 soils of the Sacramento, Foothill, and Coast Range regions that 

 were sent for examination by farmers of those regions had as 

 much as 1 per cent of humus, though for the state at large only 

 46 per cent of the 1456 soils had that amount. 



4 The method of this cursory examination for humus is as follows: 

 Take two grams of air-dried, well-mixed soil of twelve inches depth, place 

 in a test-tube of one-half inch diameter and add about ten cubic centi- 

 meters of 10 per cent solution of potassic hydrate. Boil for a few minutes 

 and allow the soil to settle. The potash dissolves the humus and produces 

 a dark color of greater or less intensity according to the amount of humus 

 present. By taking soils in which the humus percentages have already 

 been ascertained correctly, and treating them by this short method, a 

 scale of color intensities may be adopted by which approximate percent- 

 age of humus may be reached in most of the soils. 



