LA WES AND GILBERT'S EXPERIMENTS. 143 



of soda each contained eighty-two pounds of nitrogen ; and it 

 will be seen that this eighty-two pounds of nitrogen produced 

 as great an effect as the two hundred pounds of nitrogen in 

 barn-yard manure. 



Similar experiments have been made on barley, with even 

 more striking results. The plot dressed with three hundred 

 pounds of superphosphate of lime and two hundred pounds 

 ammoniacal salts per acre produced as large a crop as four- 

 teen tons of farm-yard manure. The average yield of barley 

 for nineteen crops, grown on the same land each year, was 

 forty-eight bushels and twenty-eight hundred weight of straw 

 per acre on both plots. In other words, forty-one pounds of 

 nitrogen, in ammoniacal salts, produced as great an effect as 

 tivo hundred pounds of nitrogen in farm-yard manure/ Dur- 

 ing the nineteen years one plot had received one hundred and 

 sixty-two thousand two hundred and sixty pounds of organic 

 matter, sixteen thousand four hundred and ninety-two pounds 

 of mineral matter, and three thousand eight hundred pounds 

 of nitrogen ; while the other had received only five thousand 

 seven hundred pounds of mineral matter and seven hundred 

 and seventy -nine pounds of nitrogen, and yet one has pro- 

 duced as large a crop as the other. 



Why this difference? It will not do to say that more nitro- 

 gen was applied in the farm-yard manure than was needed. 

 Mr. Lawes says : "For some years an amount of ammonia 

 salts, containing eighty-two pounds of nitrogen, was applied 

 to one series of plots, on barley ; but this was found to be 

 too much, the crop generally being too heavy and laid. Yet 

 probably about two hundred pounds of nitrogen was annually 

 supplied in the dung, but with it there was no over-luxuriance, 

 and no more crop than where forty-one pounds of nitrogen 

 was supplied in the form of ammonia or nitric acid." 



It would seem that there can be but one explanation of 

 these facts. The nitrogenous matter in the manure is not in 

 an available condition. It is in the manure, but the plants 

 cannot take it up until it is decomposed and rendered soluble. 

 Dr. Voelcker analyzed "perfectly fresh horse-dung," and found 

 that of free ammonia there was not more than one pound in 

 fifteen tons ! And yet these fifteen tons contained nitrogen 

 enough to furnish one hundred and forty pounds of ammonia. 



