Sept. lo, 1917 



Formation of ''Black Alkali'' 



573 



the absence of it. It is the writer's opinion that calcium carbonate in 

 itself has a tendency to bring the organic matter of the soil into solution, 

 and this action is hastened by the presence of all the sodium salts. It is 

 true that our limestone soils are our most fertile soils, and certainly 

 contain the most organic matter, but this is probably brought about by 

 the fact 'that the vast majority of humus-forming plants thrive best 

 upon limestone soils. An upland acid soil usually supports but a sparse 

 vegetation, and consequently accumulates little humus. The limestone 

 or calcium carbonate unquestionably stimulates the activity of the bac- 

 terial flora, and in this way, if in no other, would tend to destroy the 

 organic matter of the soil. The calcareous soils, then, probably are 

 richer in humus, not because of the protective action of lime, but because 

 of the greater supply of organic material. 



When the Citrus soils of southern California are given plenty of water, 

 the percentage of organic matter is without doubt a great factor in pro- 

 ductivity. These soils are usually extremely low in organic matter, and 

 a little variation one way or the other, brought about by proper or im- 

 proper cultural methods, sometimes shows very striking results. 



A series of pots were filled with the soil from the new Citrus station 

 site and treated as follows: 



1. Soil untreated. 



2. Soil treated with 2 per cent of calcium 



carbonate. 



3. Soil treated with i per cent of manure. 



4. Soil treated with i per cent of manure 



+ 2 per cent of calcium carbonate. 



5. Soil treated with i per cent of ground 



alfalfa. 



6. Soil treated with i per cent of ground 



alfalfa+2 per cent of calcium car- 

 bonate. 



Soil treated with i per cent of ground 

 me li lotus. 



Soil treated with i per cent of ground 

 melilotus-t-2 per cent of calcium 

 carbonate. 



Soil treated with i per cent of peat 

 (leaf mold). 



Soil treated with i per cent of peat 

 -\-2 per cent of calcium carbon- 

 ate. 



Five other soils were collected from Corona and treated with i per 

 cent of alfalfa, with and without lime. All of these pots were kept moist 

 and allowed to stand approximately for one year before being planted 

 to lemon seedlings. In every case a depressing effect was noticed when 

 lime was added to the soil. Four representative 5-month-old plants 

 are shown in Plate 62, A. 



The effect of lime is not noticeable when the seedlings are planted 

 immediately after the treatment and grown for several months. As 

 organic matter is, under the conditions of culture, the controlling factor, 

 it seems highly probable that the depressing action of lime upon the 

 seedlings is due to its indirect action upon the organic matter of the 

 soil. Even in the control soil, to which no organic matter was added, 

 the lime seems to have attacked the little organic matter existing there 

 and, in the common term, "burned it out." 

 4599°— 17 3 



