74 
SOIL SURVEY OF JACKSON COUNTY 
been found desirable to apply a small amount of the fertilizer 
with an attachment on the tobacco or cabbage setter and the 
c 
balance to be applied broadcast after the crop has developed a 
more extensive root system. For onions and other truck crops 
it is usually desirable to apply the fertilize]- broadcast previous 
to planting the crop. 
There are three factors which must be considered in relation 
to fertility and the yield of crops: First, the condition of the 
soil itself and the supplies of the various kinds of plant food 
which it offers in available form; second, the crops to be grown, 
including the kinds and amounts of plant food they require; 
and third, the use of fertilizers which will supplement the sup¬ 
ply of plant food already in the soil in a way to meet the de¬ 
mand of the crops concerned. 
Soils vary greatly in the total amount of plant food they 
contain in available form and especially in the proportion of the 
various elements required by crops. Sandy and light soils are 
generally low in most elements. Light colored clay soils are 
relatively low in nitrogen and are moderately well supplied 
with phosphates, but contain potash in relative abundance. 
Peat soils are always abundantly supplied with nitrogen which 
can be made available by proper treatment, but are practically 
always low in potash, and frequently in phosphates, and even 
sometimes in lime as well. 
With reference to crops, there are two things to consider: 
first, the relative proportion of the different elements they re¬ 
quire; second, the total quantity needed. While there are un¬ 
doubtedly slight variations in the requirements of each single 
individual crop, they can be grouped into classes fairly well. 
Such crops as small grains and grasses, including timothy, re¬ 
quire a relative abundance of phosphates and moderate amounts 
of potash and nitrogen. Such crops as corn, potatoes, tobacco, 
and sugar beets require large amounts of nitrogen and potash 
with moderate supplies of phosphates. Peas, clover, and alfalfa 
. require large amounts of phosphate, potassium, and lime, but 
under proper conditions can secure most of their nitrogen from 
the air. 
The total quantity of plant food needed depends largely on 
the total weight of the crop produced. Such crops as small 
grain, timothy, and flax require but moderate amounts of total 
