FIELD EXPERIMENTS WITH FERTILIZERS. I 23 



SPECIAL NITROGEN EXPERIMENTS. 



The special nitrogen experiments on corn, cow peas and soy 

 beans have been continued since 1895 on a set of plots that had 

 been used for similar experiments, but with other crops, for a 

 number of j'ears before this series was begun. The purpose of 

 the experiments is to study the effects of nitrogenous fertilizers 

 upon the yields of the different crops and the proportions of 

 nitrogen in them. The plan of the experiments, which has 

 been described in detail in previous reports,* consists, briefly, 

 in growing the several crops in a series of plots all of which, 

 except two without fertilizer, are supplied with uniform quan- 

 tities of mineral fertilizers, supplying phosphoric acid and 

 potash in definite amounts, and with varying quantities of 

 nitrogenous fertilizers supplying nitrogen in different amounts, 

 and in comparing the weights and the composition of the crops 

 from the different plots. The general methods of the experi- 

 ment are illustrated and explained by the diagram and the dis- 

 cussion following. 



The field used for the experiments was divided into ten long, 

 rather narrow, parallel plots, which are indicated in the diagram 

 by the numbers o, 7, 8, etc., at each end of the plots. Those 

 designated as o and 00 have received no fertilizer for twelve 

 years, while those designated as 6a and 6d have received each 

 year during the same period only the fertilizers called for con- 

 venience " mixed minerals," which consist of dissolved bone- 

 black at the rate of 320 pounds per acre, equivalent to 53 

 pounds of phosphoric acid, and muriate of potash 160 pounds 

 per acre, equivalent to 82 pounds of potash. Plots 7, 8, and 9 

 have received in addition to the mixed minerals respectively 

 160, 320 and 480 pounds of nitrate of soda per acre, equivalent 

 to 25, 50 and 75 pounds of nitrogen, while the nitrogenous 

 fertilizer added to the mixed minerals on plots 10, 11 and 12 

 consist of 120, 240 and 360 pounds of sulphate of ammonia per 

 acre, supplying 25, 50 and 75 pounds of nitrogen. 



The land on which these plots are laid out has considerable 

 slope, so that with heavy rains there is some washing of the 

 surface soil. Although this washing runs mainly lengthwise 

 of the plots, it doubtless interferes somewhat with the accuracy 



* See Reports for 1S98 and 1899. 



