leafy vegetables like spinach. On the other hand, corn, peas, beans
and other seed-forming crops need to have the nitrogen balanced with
phosphorus. Potatoes, in common with other tuber and root crops, will
utilize plenty of potassium in the development of starch.

_Sources of Plant Food._--Chemical fertilizers can be purchased at supply
stores in ready mixed condition and of analyses that will meet general
crop needs. A good formula for such a general purpose fertilizer is 4 to 5
per cent nitrogen, 7 to 9 per cent phosphoric acid and 7 to 10 per cent
potash to the ton. It is known that such a mixture will supply the food
needs of a large variety of plants in balanced amounts. Highly
concentrated mixtures are now on the market providing double the amount of
plant food in the example quoted, costing nearly twice as much but
effecting a saving by cutting in half the material handled to get the same
result. Care should be taken, in using these highly concentrated
fertilizers, to avoid contact with tender roots. A mixture for general
farm and garden purposes may contain the following ingredients:

100 pounds nitrate of soda
230 pounds sulphate of ammonia
250 pounds animal tankage (7 per cent nitrogen)
1,140 pounds superphosphate (16 per cent phosphoric acid)
280 pounds muriate of potash (50 per cent potash)
-----
2,000 pounds.

This mixture will have a formula of 4-9-7 (4 per cent nitrogen, 9 per cent
phosphoric acid and 7 per cent potassium). The individual who wishes to
mix his own fertilizer may do so by purchasing the finely ground
ingredients separately, and by means of a shovel, integrate them all into
a mixture. Home mixing will not be found profitable where small amounts of
fertilizer are used. Those who practice home mixing for the first time
should realize that most combinations of ingredients will "set" or harden
if not used immediately, necessitating the breaking up and pulverizing of
the mass. When it is broken up after curing, no further difficulty should
be experienced with "setting" if the mixture is kept in a dry place. The
advantages of home mixing for the large user lie in lower cost per ton of
plant food as a rule; confidence in the quality of the ingredients which
he should purchase on the basis of guaranteed analysis; and the setting up
of a mixture which study of his soil and the plant requirements has
convinced him is best suited for his individual case.

_Chemical Soil An