580 Journal of Agricultural Research voi. x. No. n 



Several samples of soil were taken from lemon groves, good and poor, 

 without and with the alkali crust. These soils were placed in 6-inch 

 pots and planted with very young lemon seedlings. In every case the 

 soils from the good groves gave good plants, while the soils from the 

 poor groves, the groves which had the alkali crust, gave poor plants. 

 Two representative plants are shown in Plate 62, B. Both of these soils 

 Were taken from the feeding zone (second foot) ; the poor one, therefore 

 contained little of the alkali crust which was, at the time of sampling, 

 principally on the surface, but certainly enough to affect the lemon 

 seedlings. The analysis of the crust appearing on the surface of this soil 

 is given in Table XLII, Corona grove. 



The high percentage of soluble organic matter was the most striking 

 feature of the analysis of the water-soluble salts, constituting the crusts. 

 This amounted to as high as 36 per cent of the dry material and was 

 suflicient to give color to all the solutions, ranging from brown to nearly 

 black. It will be shown later that, with the exception of sodium car- 

 bonate, none of the salts likely to occur has an appreciable effect in 

 bringing the organic matter of the soil into solution. In fact, most of 

 the lime salts seem either to be inert in this respect or else to exert a pro- 

 tective action upon the organic matter. The action of sodium carbonate 

 upon organic matter is pronounced. 



None of the crusts would react with phenolphthalein ; neither did 

 their solutions give any reaction for sodium carbonate, until they had 

 been boiled for some time. This showed that no sodium carbonate was 

 present at the time of sampling, but the color of the solution indicated, 

 if it did not prove, that sodium carbonate had at one time been present. 



ORIGIN OF BARREN, OR "SLICK," SPOTS 



The fact that a very toxic compound is formed by the union of sodium 

 carbonate and organic matter goes far to explain many of the phenomena 

 noticed in the field. At North Platte, Nebr., in the river valley, there 

 are many barren spots in the grain and alfalfa fields that are probably 

 due to this cause. These spots are usually absolutely barren, and are 

 surrounded by luxuriant growths of grain or alfalfa. By the casual 

 observer these are attributed to excessive amounts of sodium sulphate 

 or sodium chlorid, but a chemical examination of the soils showed little 

 difference in the inorganic salt content of the good and poor spots. These 

 spots are typical of a thousand that are scattered over the arid and semi- 

 arid regions of the West. The predominating alkali at North Platte is 

 sodium sulphate. The soil is rich in calcium carbonate and humus, and 

 the conditions are ideal for the reaction before described. When ex- 

 tracts from the good and poor spots from this vicinity are made, the poor 

 spots can be readily detected by the deep color of the solutions, owing to 

 the organic matter, and by a characteristic "soapy," or alkali, odor. 



