PRACTICE XXII 



SOIL ANALYSIS. DETERMINATION OF TOTAL PLANT FOOD 



Each student will select a soil in which he is especially interested. 1 



1. Dnj Matter. 



Weigh out 5 g. of the air-dried soil in a small porcelain dish, dry 

 at 100 for five hours, cool in a desiccator, and weigh. 



Weight of vessel plus dry matter 



Weight of vessel -.. 



Weight of dry matter 



Per cent of dry matter 



Av. per cent 



2. Nitrogen. 



Determine according to directions given in Practice IV. 2 



Titrations (1) cc. XH 3 



(2) cc.XH 3 



Av cc. XH 3 



Per cent X 



X in 2 million of soil 



1 Collecting Soil Samples. After one has become familiar with the typical boring 

 of the soil type, the sample is collected by taking borings from 10 to 20 different 

 places, a rod or more apart, each of which should appear to be truly representative 

 of the soil type. These borings, thoroughly mixed, should make a trustworthy sample 

 for analysis. An auger about 1^ inches in diameter, with the screw point and the 

 vertical lips filed off, is the most satisfactory instrument to use. The stem may be cut 

 in two and a steel rod of good quality welded to make the auger about 40 inches long. 



Ordinarily, samples may well be taken in sets of three : the surface, or average 

 plowed soil (0 to 6| inches) ; the subsurface, or that which can possibly be moved with 

 a subsoil plow (6 to 20 inches) ; and the subsoil (20 to 40 inches), corresponding to 

 about two million, four million, and six million pounds, respectively, of ordinary soil 

 per acre. The surface boring is made and the hole enlarged about \ inch in diameter, 

 the soil all being saved. The subsurface boring is then taken and the hole again 

 enlarged, but the extra soil is not saved. Finally, the subsoil boring is taken and the 

 soil saved from only one half (one groove) of the auger. This provides about equal 

 quantities of soil from each stratum. 



Preparation of Sample. The sample of soil after air drying is pulverized to pass 

 through a sieve with round holes 1 mm. in diameter. Any gravel which does not 

 pulverize as easily as the dried lumps of clay is weighed and its percentage deter- 

 mined, after which it is discarded. After thorough mixing, the sample is then placed 

 in a tight jar and labeled for analysis. 



2 If for any reason it is thought that the soil contains unusual amounts of nitrates, 

 the modified method given in Practice XXIV may be used. 



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