436 



ANNUAL REPORT SMITHSONIAN INSTITUTION, 1941 



Nantucket off the coast of Massachusetts, the thrifty farmers still 

 gather the drif tweed and use it as fertilizer. 



The fertilizing properties of the kelps are chiefly due to the potash 

 or potassium salts contained in these seaweeds. If plants are to grow 

 and thrive in the soil, the three essential elements necessary for their 

 growth are potassium, nitrogen, and phosphorous. The seaweeds sup- 

 ply potassium in especial abundance. The application of seaweeds in 

 bulk also has a desirable physical effect upon the soil. The majority 

 of algae when first dried and then soaked in fresh water tend to swell 

 enormously. When the dried seaweeds are plowed under into the 

 light, dry soil, this spongelike action of the seaweeds holds small res- 

 ervoirs of water in close contact with the roots of the cultivated plants. 

 There is also a large amount of organic material in the kelp which 

 decays slowly in the soil and forms humus. 



There is a great deal of variation in the analyses made of kelp since 

 the stipes of Nereocystis (pi. 9, fig. 2) and Macrocystis (pi. 7, fig. 1) 

 contain much more potash than the leaves. The proportion of stipes 

 to leaves in the samples of kelp according to Merz has a direct effect 

 upon the result obtained. 



Using figures obtained by Cameron, Frye and Rigg, Hoagland, and 

 Turrentine, Rigg calculated the amount of potassium chloride, iodine, 

 algin, and other contents in a ton of giant kelp. These figures given in 

 table 4 indicate the large amount of kelp which must be handled in 

 order to obtain a ton of potassium chloride. 



Tabu: 4. — Content of a ton- of the various Jcelps 



» No data. 



In 1912 Senate Document No. 190 appeared with a preface by the 

 President of the United States and a letter of transmittal from the 

 Secretary of Agriculture. This monumental book of about 300 

 pages contains a number of plates and maps describing particularly 

 the larger Pacific coast seaweeds and kelps and reiterates that the 

 seaweeds of the United States which have been neglected for so long 

 a period should be developed agriculturally and economically. A 

 second Government document entitled "Potash from Kelp," issued 

 by the United States and Alaska, reports further surveys of the kelp 

 beds of the United States and Alaska and reports progress in the 

 mechanical problems connected with harvesting and drying kelp. 



