
- •Introductory
- •3. Agriculture and the industries. ВЂ” Agriculture is at
- •Introductory 3
- •Introductory * 5
- •Inous substance develops on the outside of the cell-wall
- •30 The Principles of Agronomy
- •Ings around the stopper and plant be sealed to prevent
- •200 Pounds of water
- •Interaction of the elements.
- •Ing herds ; cats and birds in the control of mice and in-
- •It shall be for meat" (Genesis I. 28, 29).
- •82. How to modify structure. ВЂ” The structure of a
- •98. Need for preventing evaporation. ВЂ” The plant
- •122. Composition of soils. ВЂ” Soils are made up largely
- •133. How to determine fertilizer needs. ВЂ” In the
- •Is completed by bacteria. The carbon of the organic
- •162. Reasons for rotation of crops. ВЂ” Some sort of
- •152 The Principles of Agronomy
- •Influence the amount of erosion that will take place.
- •169. Methods of preventing erosion. ВЂ” Erosion cannot
- •180. The kernel, dry and fairly smooth, has a deep
- •174 The Principles of Agronomy
- •It grows on sands, loams, clays, and silts, avoiding the
- •184. Seed and seeding. ВЂ” Farmers had better use
- •In wheat. High nitrogen and low moisture content in
- •197. Prices vary a few cents according to grade. In
- •If a man buys a million bushels and holds it for a time,
- •221. Uses and value. ВЂ” About nine-tenths of the
- •224. Description. ВЂ” The oat plant has a fibrous root-
- •226. Distribution. ВЂ” Oats are naturally adapted to
- •Is not so good seed as a smaller one from a good hill. It
- •250. Cutting and planting. ВЂ” How large to cut the
- •266. Manufacture of sugar. ВЂ” When the factory is
- •279. Flowers and seed. ВЂ” At blossoming time, each
- •In liberal quantities, as it is likely to be where no leaching
- •270 The Principles of Agronomy
- •297. Crimson clover (Trifolium incarnatum), much
- •311. Description. ВЂ” Timothy bears a slender, spike-
- •327. Value and use. ВЂ” Orchard-grass yields about as
- •Various crops so selected, planted, and arranged as to
- •In other groups. The stalks are fine and leaves more
- •366. Distribution and adaptation. ВЂ” As might be
- •Vators, good harrows, and efficient plows have been in-
- •373. Harvesting and marketing. ВЂ” As soon as the bolls
- •380. Miscellaneous fibers. ВЂ” Manila hemp, or abaca
- •389. Sweet potatoes. ВЂ” Most of the sweet potato
- •401. Artificial selection. ВЂ” Because man has put his
- •390 The Principles of Agronomy
- •430. Work in producing various crops. ВЂ” In arranging
- •Very simple. During the last century, however, there
- •434. Machines that are seldom used. ВЂ” Some pieces
- •444. Keeping records. ВЂ” The fanner cannot, without
- •406 The Principles of Agronomy
- •621. Marketing Farm Products.
- •430 Appendix
- •Is the anther or pollen-case, and this is usually borne on a stalk
- •Ing and marketing the product. It treats in detail some eighteen individ-
122. Composition of soils. ВЂ” Soils are made up largely
of insoluble material of no food value for plants. The
amount of actual plant-food in the soil is comparatively
small, but since plants do not use large quantities of this
food, the supply is sufficient for crop production. Hil-
gard has compiled in the following table a great number
of analyses of typical soils.
These analyses show that less than 5 per cent of humid
soils is composed of plant-food and that the remainder is
largely made up of material insoluble even in strong
acid. In arid soils, the proportion of plant-food is some-
what higher, but even there, it comprises less than 10
per cent of the total soil.
The organic matter in humid soils is usually much higher
than that in soils of arid regions; but the low organic
matter of the arid soils is relatively high in nitrogen.
120
The Principles of Agronomy
Table 1. — Chemical Composition of Humid and Arid
Soils. Strong Hydrochloric Acid Analysis В»
Humid Regions
Arid Regions
Average of 696
Average of 573
Samples
Samples
1. Insoluble residue ....
84.17
69.16
2. Soluble sUica (Si02) . .
4.04
6.71
3. Alumina (AI2O3) . . .
3.66
7.21
4. Ferric iron (Fe2Q8) . . .
3.88
5.48
5. Sulfuric trioxide (SO3) . ,
0.05
0.06
6. Manganese (Mn02) . .
0.13
0.11
7. Phosphoric acid (P2O6)
0.12
0.16
8. Lime (CaO)
0.13
0.43
9. Magnesia (MgO) ....
0.29
1.27
ID. Soda (NazO) .....
0.14
0.35
11. Potash (K2O)
0.21
0.67
12. Humus
1.22
1.13
123. The analysis of soils. — In order to determine
the plant-food in a soil, the chemist takes a sample to a
laboratory, where he analyzes it. He does the sampling
very carefully, since the accuracy of the analysis depends
on the accuracy of the samples. If, for example, he
should analyze just the surface inch, his results would not
apply to the lower depths of the soil where roots often
feed ; frequently the soil varies much in composition at
these different depths. Again, if the sample should be
taken from a low place containing considerable organic
matter, it would not represent the entire field. In sam-
pling, therefore, the chemist takes soil from a number of
places in the field and at various depths and mixes all
together in order to get an average sample for analysis.
After the sample has been prepared, the method of
analysis depends on the information desired. If the total
PlanUfood of the Soil 121
plant-food is to be detennined, the soil is treated with
certain acids which dissolve the soluble matter, after
which the chemist can detennine the quantity of the
various elements in it.
124. Available and reserve plant-food. — Only a small
part of the total plant-food of the soil is available to
crops during any one year. Roots penetrate every part
of the soil, but they can absorb only material that is in
solution. Through the carbon dioxide which they give
off, the roots assist in dissolving the minerals of the soil.
Their action is slow, consequently only a small portion of
each compound can be used in any one year. This is
very fortunate, since, if all plant-food were readily dis-
solved, it would be leached out by rains or floods. The
potassium found in such minerals as mica becomes avail-
able only after years of weathering, while that in kainit
can be immediately dissolved. It is impossible, there-
fore, from a chemical analysis, to tell how much of a given
element is available to plants for immediate use without
knowing in what minerals it is contained.
125. Making plant-food available. — The making avail-
able of reserve plant-foods as fast as needed by crops is
one of the chief problems of soil management. This is
done (1) by tillage, which aids weathering agencies in
their action on soil particles; (2) by drainage, which
allows air to circulate more freely through the soil; (3)
by plowing under organic matter, which, in decaying,
helps to make the minerals soluble ; and (4) by numerous
other less important means. The nitrogen present in
the soil is made available by nitrification, which is favored
by tillage and by a desirable moisture content.
126. Quantity of plant-food removed by plants. —
Each crop uses plant-food in varying quantities. The
quantity of mineral foods taken from the soil by different
122
The Principles of Agronomy
crops is expressed by Warington in the following table, which
includes the material found in the entire harvested crop.
Table 2. Mineral Foods removed from the
Soil by Crops
Total
Crop
Yield
Ash
Nitrogen
Potash
Lime
Phosphoric
Acid
Wheat . .
Barley . .
Oats . .
Maize . .
Meadow hay
Red clover
Potatoes .
Turnips
30 bu.
40 bu.
45 bu.
30 bu.
UT.
2T.
6T.
17 T.
172 lb.
157 lb.
191 lb.
121 lb.
203 lb.
258 lb.
127 lb.
364 1b.
48 1b.
48 1b.
551b.
43 1b.
49 1b.
102 lb.
471b.
192 lb.
28.8 lb.
36.7 lb.
46.1 lb.
36.3 lb.
50.9 lb.
83.4 lb.
76.5 lb.
148.8 lb.
9.2 lb.
9.2 lb.
11.6 lb.
32.1 lb.
90.1 lb.
3.4 lb.
74.0 lb.
21.1 lb.
20.7 lb.
19.4 lb.
18.0 lb.
12.3 lb.
24.9 lb.
21.5 lb.
33.1 lb.
The table shows the variation in the relative quantities
of nitrogen, potash, lime, and phosphoric acid used by
different crops.
127. Plant-foods that are scarce. — Of the ten ele-
ments required by plants, only three may be considered
as scarce. These are nitrogen, phosphorus, and potas-
sium. In a few soils calcium and sulfur may be deficient,
but they are usually present in sufficient quantities to
supply the needs of crops for centuries.
Nitrogen is, without doubt, the element most likely to
be lacking in soils, and it is the most expensive element
when purchased; but the fact that it can be added to
the soil by the growth of leguminous plants makes its
maintenance possible in every soil. Phosphorus, which
is used in large quantities by the grain crops, is present
in exceedingly small quantities in many soils. On this
account, it becomes necessary to use phosphorus fertilizers
PlanUfood of the Sail 123
in order to maintain the fertility of these soils. Potas-
sium is usually present in fairly large quantities^ but
since it is, in the main, not available to plants, soils usually
respond to potassium fertilizers. It is probable, however,
that proper methods of increasing the availability of
reserve potassium will do much toward making unneces-
sary the heavy use of this fertilizer.
128. Exhaustion of the soil. — The possible exhaus-
tion of the soil has been discussed for many years;
niunerous different opinions have been held. Some have
contended that the plant-food supply is rapidly being
used up and that it will not be long before the soil is so
impoverished that crops will not grow. Others have
maintained that the soil is being constantly renewed and
as a result will never be exhausted. Experience has
demonstrated, however, that, if the productivity of the
soil is to be maintained at a high standard, part of the
plant-food removed by crops must be returned either as
farm manure or as commercial fertilizers. Since plant-
food is rendered available but slowly, it is probable that
crops never can entirely exhaust the soil. A lessened
supply of available food, however, greatly reduces yields
of all crops.
129. Losses in plant-food result primarily from the
removal of crops from the land, but in regions of heavy
rainfall large quantities are also removed by leaching and
by surface washing. In some of the limestone areas of
the eastern part of the United States, the rock and soil
have been leached so much that the greater part of the
original material has been removed, leaving only the more
insoluble minerals. Naturally, during this process the
more available compounds have, been carried away. In
many sections, surface erosion is responsible for the
destruction of much valuable land. The soil is, in some
124 The Principles of Agronomy
cases, washed entirely away, while in others, the main
part is retained, but the soluble material is leached from
the surface.
130. Plant-food in organic matter. — The organic
matter of the soil is composed almost entirely of dead
plants in various stages of decomposition. These dead
tissues contain a quantity of mineral matter that has
been once in solution, and is, therefore, more likely to
be available to growing plants than the minerals. Nitro-
gen is particularly important in this connection, since
practically all of the nitrogen of the soil is found in the
organic matter. Besides furnishing directly a part of the
plant-food, organic matter assists, by its decay, in render-
ing available the mineral matter of the soil.
131. Relation of plant-food to value of a soil. — In
order that a soil may be valuable, it must have an ample
supply of plant-food ; but this is by no means the only
consideration. Farmers sometimes submit a small sample
of soil to a chemist with the request that he analyze it
and tell what the land is worth. Those who are familiar
with soil study understand that it is impossible by merely
knowing the total quantity of plant-food to tell the exact
value of any land. Such questions as drainage, aeration,
mositure supply, texture, and many other things help
to determine what a soil can produce. All these factors
must be taken into consideration in estimating the value
of land and in outlining methods of management.
SUPPLEMENTARY READING
Soils, Lyon, Pippin, and Buckman, pp. 327-374.
Fertilizers and Crops, L. L. Van Slyke, pp. 105-116.
The Soil, P. H. King, pp. 107-134.
Soils, E. W. Hilgard, pp. 313^21.
Physics of Agriculture, P. H. King, pp. 69-106.
Pirst Principles of Soil Pertility, A. Vivian, pp. 3-46.
CHAPTER XII
MANURES AND FERTILIZERS
Plants require for their growth an available supply
of various mineral foods. These should be present in
the soil in a balanced condition in order that the plants
may find the most congenial environment. Crop yields
are decreased if any one of these necessary elements is
present in exceptionally small quantities. Even if all
other conditions are favorable, the producing power of
most soils could be materially increased by simply chang-
ing the available supply of one or two elements. The
addition of a fertilizer may effect this readjustment.
Where crops are raised continuously on land and re-
moved each year, a certain amount of plant-food is carried
away. An unreplenished deposit of money in the bank,
no matter how large, will in time be exhausted if contin-
ually drawn out. The plant-foods in the soil may be
considered in much the same way, and while this analogy
is not entirely true, yet the same principle holds.
Some soils contain a very great store of plant-food, but
even such will not continue to endure abuse without
protesting by giving reduced yields. If a permanent
system of agriculture is to be maintained on any soil,
no matter how rich, at least a part of the mineral matter
that is removed must be returned either in the form of
farm manure or commercial fertilizers.
125
126 The Principles of Agronomy
Materials are often applied to the soil for their indirect
action as well as for the plant-food which they add.
Fann manure improves the physical condition of the soil ;
lime corrects acidity and flocculates the particles of fine
clay ; other fertilizers help to render available the reserve
store of plant^food in the soil.
132. Types of fertilizers. — The materials added to
the soil either as direct or indirect fertilizers are numer-
ous. By far the most important of these is farm manure,
which is composed largely of animal excreta mixed with
litter. Of the fertilizers purchased from the outside, the
most common are those applied for the nitrogen, phos-
phorus, and potassium they contain. These are usually,
but not always, in the form of mineral salts. Other
materials called amendments are used for their indirect
action on the soil rather than for the direct plant-food
they furnish. In addition to these substances, which
must be hauled to the soil, it is a common practice to
grow certain crops which serve a similar purpose. These
are usually the legumes. In order for them to be of use
as a fertilizer, they are plowed under.