102 MARINE PRODUCTS OF COMMERCE 



the water-soluble potassium compounds to growing crops were discovered, they 

 explained, in large measure, the advantages derived from the use of seaweeds 

 and seaweed ashes; for these substances usually contain relatively high percentages 

 of potash. 



The use of seaweed as manure is the most general and in some countries the 

 most important. In Great Britain, since the potash and iodine industries have been 

 abandoned, the use of seaweed as fertilizer has become about the most important 

 seaweed industry. No statistics relative to the amount of seaweed used as manure 

 are available since it is rarely sold or transported for long distances. The algae 

 are usually collected in the vicinity of the seacoast by farmers who apply them to 

 their land. Some seaweed is gathered in the New England states; but, except for 

 the giant kelps on the California coast, its use for fertilizer in the United States 

 has always been of only minor importance. Evidently this is because the United 

 States possesses a great abundance of other more easily accessible fertilizing 

 materials. 



In addition to the relatively high potassium content (varying from 3 to 17 

 per cent) the dry matter of seaweeds contains from 1.0 per cent to 7.0 per cent 

 nitrogen. In most common seaweeds the amount of nitrogen in the dry matter 

 varies between 2 and 3 per cent. Much smaller amounts of phosphorus, calcu- 

 lated as phosphoric acid (P2O5), are present; the maximum amount is about 1.0 

 per cent and the minimum about 0.2 per cent of the dry weight. The total amovmt 

 of fertilizing constituents present in fresh seaweed is comparable to the amount 

 present in barnyard manure. However, seaweed contains a much greater propor- 

 tion of potassium salts, a much smaller proportion of phosphoric acid, and about 

 the same proportion of nitrogen. 



For certain root crops, such as beets and potatoes, the use of seaweed as 

 fertilizer is particularly desirable because they need larger proportions of potash 

 than most other crops. Since seaweed is especially low in phosphorus and rela- 

 tively low in nitrogenous constituents, materials high in these substances should 

 be mixed with it to obtain a complete and balanced fertilizer. 



Nearly all of the potash in seaweed is water-soluble and, therefore, immediately 

 available for plant use. The nitrogen and phosphoric acid which it contains be- 

 come available only when the seaweed decays. This takes place relatively slowly 

 in the soil. Thus, it is not especially valuable as a top-dressing as it has little 

 water-solubility or readily available nitrogen. If it is mixed with barnyard manure 

 before application, it decays more rapidly when it is applied and the nitrogen 

 and phosphorus become available more quickly. 



Algae Used for Stock Feed. In Norway, Scotland, and Ireland herds pasturing 

 along the seashore graze on the fuci exposed at low tide. In Norway and Scotland 

 Irish moss and various rockweeds are gathered, boiled, mixed with meal, and fed 

 to horses, pigs, and cattle. Cattle and horses are not usually fond of seaweed un- 

 less they are accustomed to eating it. Furthermore, seaweed is considered poor 

 animal feed since it is not readily digested. 



Recently, however, there have been attempts to manufacture chicken and stock 

 feed from rockweed. A "seaweed meal," which is prepared by drying and grinding 

 rockweed (Fticus vesiculostis) , has been put on the market at Harsted, Norway. 

 This feed, which was said to contain too much inorganic matter, had the follow- 

 ing proximate analysis: 



