POT EXPERIMENTS WITH FERTILIZERS. 1 55 



tracks which extend into the yard. On these tracks are placed 

 trucks for holding the pots of soil in which the plants are 

 grown. The pots used are 18.5 inches deep and 10 inches in 

 diameter and will hold from 60 to 80 pounds of soil, sand and 

 gravel. The pots are made of heav}^ galvanized iron and are 

 fitted with half-inch lead pipes on the outside which are at- 

 tached in such a way as to allow for watering at the bottoms 

 of the pots. 



The soil used and the method offillhig the pots. — The soil used 

 in the experiments was taken from field plots which have been 

 supplied with nothing but mineral fertilizers since 1890. This 

 soil was used because there seemed to be but little organic mat- 

 ter in it, and judging from the crops grown on it in recent 

 years there was but little available nitrogen present. The soil 

 was thoroughly mixed before it was put into the pots. In fill- 

 ing the pots about two inches of coarse gravel was placed in 

 the bottom of each, and this was covered with a thin la3'er of 

 sand; the soil was then added in layers of about one inch in 

 thickness, each layer being well tamped as it was filled in. In 

 the earlier experiments from 50 to 60 pounds of soil were used 

 in each pot, the quantity varying somewhat for the different 

 series, but uniform for each pot in the same series. 



In the experiments of 1901 all of the soil which had been 

 used in the experiments of 1900 was discarded and a new lot 

 was obtained, as in previous years, from the mineral plots in 

 the field experiments. This was placed in a heap and thor- 

 oughly mixed; the gravel and sand was placed in the bottom 

 of each pot, and then 55 pounds of the mixed soil was added. 

 The moisture content of the soil was determined by drying 

 samples at 105° C; the soil in pots i to 12 contained 13.25 per 

 cent, and that in the other pots 12 per cent. The weights of 

 the filled pots was ascertained, to be used as explained later in 

 keeping the percentage of moisture of the soil within a certain 

 range. 



Adding the fertilizer. — To each pot in the whole experiment 

 mineral fertilizers were applied uniformly as follows: phosphate 

 of potash 2.54 grams, sulphate of potash .50 gram, carbonate 

 of lime 4.00 grams. Some of the pots received no other fertil- 

 izer besides the minerals, while other pots received nitrate of 



