16 



quantities of these salts are readily tolerated. For other plants and in 

 other soils these figures may vary to a greater or less extent. 



The conditions are much more complicated where we find mixtures 

 of the different salts in the drae soil. If the effect of the different 

 salts were simply additive, then we could easily calculate what their 

 total effect would be. But the effect of one salt not only does not 

 intensify the action of others, but en the contrary there are certain salts 

 which will counteract the effect of others. Thus sulfates in general will 

 mitigate the effects of carbonates, bicarbonates and chlorides, and calcium 

 salts in general will counteract sodium and magnesium salts. For this 

 reason it is sometimes very difficult to interpret the results of analyses 

 of soluble salts contained in a given soil. 



While some plants are quite resistant to the effect of soluble salts, 

 others are easily harmed by even small amounts. There are certain grasses 

 and other plants that grow well only in places highly impregnated with 

 salt, But they are very few. Among cultivated plants, beets, barley and 

 asparagus are most resistant. Another important point is, that plants 

 usually are much less resistant when young than after they have fully 

 developed and are naturally stronger. Thus the salt content of a soil 

 may, during the growth of a plant decidedly increase, without detriment 

 to the plant, and finally reach a concentration which would have killed 

 the plant in the earlier stages of its growth. A good example of this 

 behavior is alfalfa which shows little resistance to salts when young, but 

 wbicb will stand enormous amounts in subsequent years without showing 

 signs of injury. 



Tbe character of the soil is also very important in this connection. 

 In stiff soils the tolerance for salts is usually much less than in light 

 soils which can be more easily cultivated, thus helping the plant in its 

 attempt to resisl the effeet of the salts. Tn soils high in carbonate of lime 

 the different salts are less injurious than in those devoid of lime, because, 

 as we have already seen, lime salts counteract the effect of sodium and 

 magnesium salts. A high nitrogen content in soils is also helpful against 

 the bad effect of salts in the soil. 



Having thus reviewed the effects of salts in soils in a general way 

 we sliall now turn to the sugar cane in particular which is the natural 

 crop for the coast lands of Porlo Rico. As the cane is not grown for its 

 total weight but for the sugar contained in it. we have to make a distinc- 

 tion between tbe influence of salts on the growth of the cane and that of 

 its composition. 



There is an apparent difference of opinion among authors concern- 

 ing the effect of salt on the srrowth of the cane. Some say that cane will 

 thrive on soils impregnated with salt ( 1 ). Tn Jamaica, Barbados, Trinidad 



(1) Journal d' Agriculture Tropicale, Vol. 1. p. 145. 



