112 MAINE AGRICULTURAL EXPERIMENT STATION. I914. 



potash. In field experiments potash has rarely been a deter- 

 mining element in the yield of the potato crop. 



While the writer believes it to be important for Maine that 

 as much potash be put in the commercial fertilizers as can be 

 used under the present circumstances, it is more than probable 

 that by more thorough preparation of the soil, the use of liberal 

 quantities of high grade fertilizers carrying ecjually as much 

 nitrogen as in the past and perhaps rather more phosphoric 

 acid, and with as much potash as can be obtained, there will be 

 no serious shortage in the crops for 1915. 



While there are some chemicals, such as lime, gypsum, and 

 chloride and sulphate of sodium, which are supposed to be- more 

 or less efifective in making soil potash available, they can be 

 only slightly depended upon. When potatoes enter into the 

 rotation lime cannot be used because of the danger of scab. 

 Gypsum (land plaster) and sodium chloride (common salt) are 

 about the only chemical agents that can be economically and 

 safely used. All commercial fertilizers carry as a byproduct in 

 the manufacture of acid phosphate, considerable quantities of 

 gypsum. As land plaster is not an expensive product it prob- 

 ably will be advisable to use it at the rate of perhaps half a ton 

 per acre. It will also be advisable to use a small amount, per- 

 haps 300 pounds per acre, of common salt. 



If the present conditions continue we plan to use both at 

 Highmoor Farm and at Aroostook Farm in 1915 a fertilizer 

 carrying about five per cent of nitrogen, eight to ten per cent 

 of available phosphoric acid and all the potash that we can 

 obtain up to seven per cent. One-third of the nitrogen will be 

 in the form of nitrate, one-third in the form of ammonia salts 

 and one-third in the form of high grade organic nitrogen. The 

 amount of phosphoric acid will depend upon the amount of 

 potash that can be had. The more potash the less the phos- 

 phoric acid. If the potash falls below five per cent we shall 

 apply broadcast about 1000 pounds of land plaster and 300 

 pounds of common salt per acre. As the land plaster is quite 

 insoluble it must be finely ground. The common salt is readily 

 soluble in water and it can be safely applied in as coarse form 

 as so-called Liverpool salt. 



It is to be remembered that this formula is not based upon 

 the results of definite field experiments, nor is it one that the 



