HINTS ON SOILS AND FERTILIZERS 21 
just as much as that one element is lacking. 
In fact,' the lack of just one element may be 
considered a measuring stick for the yield of 
the crop being raised. If this one element is 
just half enough to supply the needs of the 
crop, then we may consider that we will get 
just half a normal crop, other conditions being 
favorable. 
Many farmers wonder as to the best way 
to find out what element is lacking in their 
soils. It is a common experience to find farm¬ 
ers sending samples of some unproductive piece 
of land to their Experiment Station, to have 
it analyzed, chemically, so they may discover 
this elusive element. But this method fails 
to give the farmer the information that he 
seeks, because, while the chemist can analyze 
his soil, and find out the elements contained 
in the soil, as well as finding the different pro¬ 
portions of the various elements, he cannot tell 
the farmer how much of each element is avail¬ 
able. And this is the point over which the 
farmer is concerned. He doesn’t care a snap 
if he has sixty per cent- of nitrogen locked up 
in his soil, if he is unable to learn the amount 
that is available for plant food. Hence, this 
method is of little use to the farmer who wishes 
to determine the needs of his soil. 
There is a method, however, that is very prac¬ 
tical, and one which any farmer can use, al¬ 
though the results cannot be determined very 
speedily. This method is known as the test 
plot method. As has been stated in a previous 
chapter, the elements most used by plants, out¬ 
side of the gaseous elements, are nitrogen, phos- 
