36 Journal of Agricultural Research voi. jv.no. i 



Pelagophycus porta ranks next to the Nereocystis in availability, while 

 Macrocystis pyrifera, the commercial variety, is the least available of all. 

 The studies carried through with this material prove that when very 

 completely oven-dried this kelp is changed in the soil with extreme slow- 

 ness. When sun-dried so that it can be readily ground, it requires 

 about II weeks to ammonify and to begin to nitrify appreciably. In 

 Series IV a slight gain is shown by one quantity of air-dry Macrocystis 

 at the end of three weeks. This kelp was dried for the shortest possible 

 time in the sun and the drying was then completed in the incubator room 

 at 28° C. The other samples in Series IV, which contained greater 

 amounts of moisture, were all more available. It would therefore appear 

 that ]\Iacrocystis should be dried and ground at as low a temperature as 

 possible. Commercially, artificial heat will probably be necessary for 

 drying. This drying will have to continue till the kelp is crisp and prac- 

 tically water-free, but should not be carried on for a longer time than 

 may be necessary to have it attain this condition. 



The addition of moderate quantities of Nereocystis to the soil has not 

 caused any great inhibition to either ammonification or nitrification. 

 With Macrocystis, however, very appreciable inhibition is at first shown. 

 As time goes on, this is gradually less evident. With the smaller amounts 

 of kelp used in held fertilization, the inhibition would undoubtedly be 

 less and would probably be sooner counteracted. 



CONCLUSIONS 



(1) In preparing dried and ground kelp as a fertilizer the availability 

 or readiness with which the nitrogen in it is changed to ammonia and 

 nitrates in fresh field soil was found to vary Mith different species and 

 with the manner of preparation. 



(2) The nitrogen of Nereocystis luetkeana is relatively very available, 

 while that of Pelagophycus porra is less readily changed. These two 

 varieties are of minor commercial importance. 



(3) Macrocystis pyrifera, the commercial variety, is very slowly 

 changed in the soil. 



(4) The availability of the nitrogen of M. pyrifera is greatest when 

 the kelp is added in a fresh or only partially dried condition. 



(5) The availability of its nitrogen decreases materially when Macro- 

 cystis is fully dried. 



(6) Removing a large portion of the salts from either fresh or dry 

 Macrocystis by leaching does not cause it to decompose more readily. 



(7) Macrocystis must be dried till crisp in order to grind readily. 

 This drying should not be continued longer than necessary, and the kelp 

 should not be scorched or overheated. 



(8) The addition of moderate quantities of Nereocystis to a sample of 

 fresh soil in the laboratorv did not cause an'v great interference with 



