The _fifteenth_ season (1857-8,) gives a yield of 18 bushels of wheat per acre on the continuously unmanured plot, and nearly 39 bushels on the plot continuously manured with 14 tons of barnyard manure. Mixed mineral manures on 5_a_ and 5_b_, give a mean yield of less than 19 bushels per acre. Mixed mineral manures and 100 lbs. ammonia-salts, on plots 21 and 22, give 23¼ bushels per acre. In other words: 25 lbs. ammonia, gives an _increase_ of 4¼ bush. (100 lbs. ammonia-salts) 50 ” ” , ” ” ” ” 10 ” (200 ” ” ” ) 100 ” ” , ” ” ” ” 20 ” (400 ” ” ” ) 150 ” ” , ” ” ” ” 23 ” (600 ” ” ” ) 200 ” ” , ” ” ” ” 23 ” (800 ” ” ” ) “It takes,” said the Deacon, “about 5 lbs. of ammonia to produce a bushel of wheat. And according to this, 500 lbs. of Peruvian guano, guaranteed to contain 10 per cent of ammonia, would give an increase of 10 bushels of wheat.” “This is a very interesting matter,” said I, “but we will not discuss it at present. Let us continue the examination of the subject. I do not propose to make many remarks on the tables. You must study them for yourself. I have spent hours and days and weeks making and pondering over these tables. The more you study them the more interesting and instructive they become.” The _sixteenth_ season (1858-9), gives us a little over 18¼ bushels on the unmanured plot. On the plot manured with 14 tons farmyard manure, 36¼ bushels; and this is the highest yield this season in the wheat-field. Mixed mineral manures alone, (mean of plot 5_a_ and 5_b_), give 20½ bushels. 25 lbs. ammonia (100 lbs. ammonia-salts), and mixed minerals, give 25¼ bushels, or an _increase_ over minerals alone of 4¾ bushels. 50 lbs. ammonia, an increase of 9¼ bushels. 100 ” ” ” ” ” 14 ” 150 ” ” ” ” ” 14 ” 200 ” ” ” ” ” 14¼ ” The season was an unfavorable one for excessive manuring. It was too wet and the crops of wheat when highly manured were much laid. The quality of the grain was inferior, as will be seen from the light weight per bushel. The _seventeenth_ season (1859-60,) gives less than 13 bushels per acre on the unmanured plot; and 32¼ bushels on the plot manured with 14 tons farm-yard manure. This season (1860), was a miserable year for wheat in England. It was both cold and wet. Mixed mineral manures, on plots 5_a_ and 5_b_, gave nearly 16 bushels per acre. 25 lbs. ammonia, in addition to the above, gave less than 15 bushels. In other words it gave no _increase_ at all. 50 lbs. ammonia, gave an _increase_ of 6 bushels. 100 ” ” ” ” ” ” 11¾ ” 150 ” ” ” ” ” ” 15¼ ” 200 ” ” ” ” ” ” 16¾ ”