ey have yielded, and continue to
yield, as good crops as adjacent plats which have received yard manure
every two years in place of commercial fertilizer."

Soil Analysis.--There is wide misconception regarding the value of
chemical analysis of the soil as an aid in making choice of a
fertilizer. Analysis has shown that some soil types are relatively
richer in plant-constituents than are others, and it has shown abnormal
deficiency in some types of limited area. It has given us more
knowledge of soils, but as a guide to fertilization in particular
instances it usually has no value. The samples used by an analyst are
so small that the inaccuracy in his determination may easily be greater
than the total amount of plant-food in a very heavy application of
commercial fertilizer. A field that has been reduced to temporarily low
productive power by heavy cropping or bad farming methods may show a
greater content of plant-food than another field that is in a highly
productive condition. This is a fact difficult of acceptance by some
who want the aid of science, but such are the present limitations. The
weight of a fertilizer application is so small in comparison with the
weight of the surface part of an acre of land that the use of a ton of
fertilizer may not be detected in the analyst's determinations, and
moreover his determinations of actual availability in the soil's
supplies are not serviceable in the selection of a fertilizer for any
particular field and crop.

Physical Analysis.--Chemical analysis is costly and unsatisfactory as a
guide to fertilization. Physical analysis by a competent man may have
distinct value, and especially to one lacking experience with his soil.
The mapping of soils by national and state authorities has given pretty
accurate knowledge of hundreds of soil types, their location and
characteristics, and when a soil expert obtains a sample of soil and
the history of its past treatment, he can assign it to its type and
give to its owner dependable advice regarding its crop-adaptation and
probable fertilizer requirements.

The Use of Nitrogen.--There is no fully satisfactory way of determining
the kind and amount of fertilizer that should be used at any particular
time for any one crop. Perfection in this respect is no easier in
attainment than in other matters. There are, however, means of arriving
at conclusions that are a valuable guide.

In a general way, nitrogen is in scant supply in all wor