PRACTICE XXXIII 



DETERMINATION OF THE PLANT-FOOD REQUIREMENTS 

 OF A SOIL BY A POT-CULTURE TEST 



Procure sufficient soil to fill a series of ten ordinary four-gallon 

 butter crocks. Collect the soil to a depth of 10 inches, keeping the 

 first five inches separate from the second five inches. Air-dry the 

 soil and fine it so that it will pass through a i-inch mesh sieve. 

 Separately mix the two portions very thoroughly. In the center of 

 each pot make a drainage hole about inch in diameter, cover this 

 with a piece of copper-wire netting, and upon this place a bunch of 

 glass wool extending over the hole. Fill each pot to the depth of 5 

 inches with an equal weight of the second depth of soil, pressing it in 

 firmly to represent as nearly as possible natural conditions of com- 

 pactness. With an equal weight for each pot of the first depth of 

 soil, which, when thoroughly compacted, will fill the pot within \ 

 inch of the top, mix very thoroughly the kind and amount of material 

 or materials, as indicated below, and bring the mixture into the pot. 



PLAX FOR POT-CULTURE TEST 



Plant the series with wheat, oats, timothy, or other suitable crop, 

 by removing a layer of the surface soil, distributing the seed, and 

 returning the soil removed. A sufficient number of seeds should be 

 planted so that a uniform number of strong seedlings may finally 

 be left in each pot. (About 20 plants are satisfactory for cereals.) 

 Place the series of pots either in a greenhouse or out in the open, 

 with arrangements so that they may be protected from severe wind 

 or heavy rain. Water as is necessary, preferably with ammonia-free 

 distilled water or with very pure rain water. 



When mature the crop should be harvested uniformly, thoroughly 

 air-dried, and weighed, afterward separating the grain from the 

 straw, in the case of cereals, and weighing the grain. Calculate 

 the applications made, and the yields secured, on the acre basis. 



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