260 TALKS ON MAJfUEES. 



least, they have very little eflfect, 400 lbs. giving an increase of only 

 five bushels per acre. One hundred pounds of plaster per acre gave 

 an in 'rease of six bushels. Plaster and ashes combined, an increase 

 per acre of 15 busheLs. 



One fact is clearly brought out by these experiments : that this 

 soil, which has been under cultivation without manure for many 

 years, is not, relatively to other constituents of crops, deticieiit iu 

 potash. Had such been the case, the sulphate of ammonia and 

 supcrphospiiateof lime — manures wliich coataiu no potasli — would 

 not have given an increase of 84 bushels of potatoes j)er acre. 

 There was sufficient potash in the soil, in an available condition, 

 for 179 bushels of potatoes per acre ; and the reason wliy the soil 

 without manure produced only 95 bushels per acre, was owing to 

 a deficiency of ammonia and phosphates. 



Since tljese experiments were made, Dr. Voelcker and otiiers have 

 nvide similar ones iu England. Tlie results on the whole all point 

 in one direction. They show that the manures most valuable for 

 potatoes are thosj rich in nitrogen and phosphoric acid, and that 

 occasionally potash is also a useful addition. 



"There is one thing I should like to know," said the Doctor. 

 " Admittmg that nitrogen and phosphoric acid and potash are the 

 most important elements of plant-food, hovv many bushels of po- 

 tatoes should we be likely to get from a judicious application of 

 these manures?" 



"Tliere is no way," said I, "of getting at this with any degree 

 of certauny. The numerous experiments that have been made in 

 England seem to show tliat a given quantity of manure will produce 

 a larger increase on poor land than on land in better condition." 



In England potatoes are rarely if ever planted without manure, 

 and the land selected for tliis crop, even witliout manure, would 

 usually be in better condition than the average potato land of this 

 section, and consequently a given amount of manure, applied to 

 potatoes here, would be likely to do more good, up to a certain 

 point, than the same amount would in England. 



Let us look at some of the cxpenments that have been made in 

 England : — 



In tlie Transactions of the Highland and Agricultural Society of 

 Scotland for 1873 is a prize essay on " Experiments upon Potatoes, 

 with Potash Salts, on Light Land," by Charles D. Hunter, F. C. S., 

 made on the firm of William Lawson, in Cumberland. Mr. Hun- 

 ter " was cliarircd witli the manuring of the farm and tiic purehas- 

 inur of cliemical maimres to the annual value of £2,000," or say 

 110,000. 



