389. Sweet potatoes. ВЂ” Most of the sweet potato

(Iporncsa Batatas) crop of the United States is grown in

the South. Loose, friable soils favor best growth of the

enlarged roots which are the edible plant parts. Cultiva-

tion is very similar to that given " Irish " potatoes.

Shoots from the roots are transplanted for a new crop

(Fig. 86). Since frost injures the crop readily, the plant is

harvested before cold weather sets in.

Sweet potatoes are used almost entirely for human

consiunption, forming in the South a more important

article of diet than the common potato (Fig. 87). They

are fed to hogs to some extent and the fields are used

for pasturing hogs, which are turned in to " root " out the

potatoes.

The Principles of Agronomy

Flo. 86, — Sweet potato plaats started in

Fig. 87. — In the South sneet potatoes are an important crop.

Fibers and Miscellaneous Crops 349

390. Fruits. — Apples, peaches, pears, cherries, citrus-

fruits, and small-fruits are all grown extensively in various

parts of the country on such large areas that they might

rank as field crops, though, of course, they are classed

as horticultural products. Formerly, they were grown

in small plots, but with more extensive culture their

problems are akin in some respects to grain and forage,

differing, however, in prunmg, spraying, thinnmg, pack-

ing, and marketing.

Irrigation, cultivation, and fertility of orchard soils

depend on the same principles that influence farm crops.

Weeds must be kept down by plowing between the trees

or by using cultivators (Fig. 89) ; the soil must be kept

in good tilth by the addition of farm manure or the plow-

ing under of cover crops. Clovers are probably best for

this purpose. In some cases, at least, it seems advisable

to have the rows in sod instead of bare.

391. Truck crops. — In the neighborhood of canneries,

large acreages of tomatoes are grown under contract.

This crop is usually transplanted from hot-beds and

cultivated much as potatoes until harvest season, when

the tomatoes are picked by hand and hauled to the fac-

tory.

Peas, beans, cucumbers, cauliflowers, and other garden

crops are grown near factories for canning purposes, or

near large cities that afford ready markets. Cantaloupes

and melons are also grown under peculiarly favorable

conditions and shipped or hauled to market.

Squash and pumpkins are grown on many farms for

use in the house, or for cattle- and hog-feed. They are

usually planted in hills five or six feet apart and culti-

vated as long as the vines permit. When the vines die

from frost or from maturity, the squash and pumpkins

are gathered and stored under cover.

360 The Prindplea of Agronomy

Fio. 88. — Greenhouse crops are in demand near large cities.

Fig. 89. — A good implement with whioh to cultivate on t, large a

Fibers and Miscellaneous Crops 351

392. Timber crop. — With the depletion of many

forest lands, the price of lumber has risen to such an ex-

tent that it is profitable for farmers in many localities

to grow small patches of timber. Hardwood for repair

of various machines and tools ought to be at hand at all

times. In some sections, a few trees may be grown for

this purpose and kept free from low branches by pinching

off branch buds and by pruning wisely.

393. Other crops. — Tea, coffee, nuts, tropical fruits,

rubber trees, sugar maples, poppies for opium, hops, cacti,

and dye and medicinal plants are grown to some extent

in parts of the world. Besides these, countless plants are

grown in small gardens for home use. Finally, the

flower-growing industry has assumed importance (Fig. 88).

Greenhouses and home-, roof-, and house-gardens abound

with innimierable plants bearing beautiful flowers, leaves,

or stems.

SUPPLEMENTARY READING

Cotton, C. W. Burkett.

Hemp, Boyce.

Field Crops, Wilson and Warburton, pp. 241-255, 363-386.

Field Crop Production, G. Livingston, pp. 337-357.

Forage and Fiber Crops in America, T. F. Himt, pp. 304-402.

Forage Crops, E. B. Voorhees, pp. 292-310.

Forage Plants, C. V. Piper, pp. 589-595.

Southern Field Crops, J. F. Duggar, pp. 248-424, 484-547.

Cyclopedia of American Agriculture, Vol. II, pp. 221-224, 226-229,

247-258, 281-303, 377-380, 380-384, 388-391, 494-410, 530-

534, 554-559, 631-636, 639-656.

U. S. D. A. Farmers' Bulletins :

No. 27. Flax for Seed and Fiber.

36. Cotton Seed and its Products.

47. Insects Affecting the Cotton Plant.

48. The Manuring of Cotton.

164. Rape as a Forage Crop.

352 The Principles of Agronomy

209. Controlling the Boll Weevil in Cotton Seed and at

Ginneries.

211. The Use of Paris Green in Controlling the Cotton

Boll Weevil.

217. Essential Steps in Securing an Early Crop of Cotton.

223. Miscellaneous Cotton Insects in Texas.

226. Building up a Run-down Cotton Plantation.

274. Flax Culture.

276. The Advantage of Planting Heavy Cotton Seed.

290. The Cotton BoUworm.

302. Sea^Island Cotton.

314. A Method of Breeding Early Cotton to Escape Boll

Weevils.

333. Cotton Wilt.

344. The Boll Weevil Problem.

364. A Profitable Cotton Farm.

433. Cabbage.

500. The Control of the Boll Weevil.

501. Cotton Improvement Under Weevil Conditions.

512. The Boll Weevil Problem.

519. An Example of Intensive Farming in the Cotton Belt.

577. Growing Egyptian Cotton in Salt River Valley, Ari-

zona.

601. A New Method of Cotton Culture and its Application.

625. Cotton Wilt and Root-Knot.

CHAPTER XXVII

IMPROVEMENT OF CROPS

Though our crops are far superior in many respects to

those of our ancestors, there still remains room for im-

dreamed-of improvement. Every farmer knows he will

have some small and some knotty potatoes ; that some of

the wheat will shrink or lose color, become smutty or

lodge and rust; that some ears of corn will be nearly

bare, and that most ears will not be entirely filled with

deep kernels. Regardless of its care, a farm returns

lower yields some seasons than others; no matter how

much caution is used in cultivation and selection of seed,

poor stands in some parts of the field will be found. The

farmer knows that his yield from each acre is never so

large as it might have been had not the unexpected or

the unavoidable happened, or had the field been handled

a little differently. That much can be done to improve

crops is apparent. A plant-breeding field is seen in Fig.

90 and a hand thresher in Fig. 91.

Experience has proved that careful cultivation, rota-

tion, manuring, and irrigation may increase, and even

double the yields in some cases. These gains last only

for a short period of time, that is, until the effect of the

extra care has passed. Next year it must be repeated

to secure the extra yields. If plants could be found that

would produce more, simply because they were higher

2a 353

354 The PriTtdples of Agronomy

yielders, whatever increase came might be expected year

after year. Nor would this bar the opportunity for

improvement by superior cultural methods; indeed, it

often happens that the better the plant the more readily

it responds to additional care.

Hmit ' estimates that if grain plants could be obtained

that would produce one additional kernel in each head or

on each ear, the total yield of the United States would

increase by 5,000,000 bushels of com, 15,000,000 bushels

of oats, and 1,500,000 bushels of barley. One additional

potato in each hill would total 21,000,000 extra bushels

of potatoes.

394. What is improvement ? — Perhaps the most im-

portant thing in crop improvement is increase in yield-

Better quality also deserves attention in that it increases

the usefulness and market price of the product. Clean,

uniform potatoes free from disease are much sought after,

particularly for seed. Growers would pay extra for them.

' Cereali in America, pp. 14-15.

Improvement of Crops 355

Pliimp wheat of uniform texture; soft, leafy bay; or

apples alike in color, flavor, and size bring extra prices..

Both yield and quality are resultants of several complex

factors. They are ends — goals toward which improve-

ment must be pushed. Not always can this be done

directly, for it may be that one factor alone, such as disease

in potatoes, is hindering. Improvement in yield or quality

Flo. 91. — Hand thresher for work m plBtit-breeding.

is most often made by looking back to find the cause of

the defect. One muddy tributary will discolor all the

river below its entrance; if this is cleared, the whole

stream is clear. If a crop lacks resistance to drouth,

to beat, to frost, to insects, to disease, to alkali, or to

• water, it may be injured seriously any time by a single

weakness, though it has strength in all other respects.

" A chain is no stronger than its weakest link."

356 The Principles of Agronomy

•

Should a variety of com from a section with a long

growing-season be brought into a district with a shorter

one, it could not mature ; and whatever its possibiUties

in other respects, not much will actually come from it.

Though climatic adaptation is paramount, general suit-

ability to soil and cultural methods is also essential.

Potatoes succeed best on loose, fertile soils and under

clean cultivation. A selection of adapted varieties is

the first step toward better crops. Experiment stations

are continually testing crops to find the strains best

suited to their localities.

396. Ideal sought. — Improvement consists largely of

advancement toward some desired quality in a given

crop. The factors that determine best growth are tools

of the plant-breeder who can wield them eflFectively.

This he can do only when he knows where to strike and

how. We have much to learn about plant-breeding, but

even if we knew all, no great gains could be made unless

the breeder had an ideal plant clearly in mind. Just as

an architect sees and always works to build the house he

has in mind, so must the plant-breeder know just what he

desires. Nor must the ideal change. Imagine the kind

of house a person would have if he changed his mind each

week while he was building it. If his ideal is wrong, he

will come out wrong ; if he has a good plan, he will come

out right, provided he does not change. So it is with the

plant ; the first ideal must be right, then all effort must

bend toward it. But this ideal may be impossible or

so nearly so that it is not feasible. We can hardly hope

to grow grass that is all leaves, but we can accomplish

much in reducing the percentage of stem. The ideal

sought should be possible, valuable, distinct, and constantly

striven for.

Improvement of Crops 357

METHODS OF IMPROVEMENT

Crops may be improved by three general methods : (1)

better culture, (2) attention to the purity and strength of

seeds, and (3) plant-breeding, which consists of selection

or of crossing and selection.

396. Cultivation. — Though fann methods have im-

proved very materially since the Civil War and even in

the last few years, many farms do not get cultivation

that comes up to the best knowledge of the owners, much

less up to the standard urged upon them by agricultural

colleges and farmers' organizations. A more systematic

practice of the care and use of farm manure, good plowing,

early spring harrowing, wise rotation, moderate irrigation,

clean farming, treatment for insects and plant diseases,

harvesting in the proper way and at the proper time all

deserve attention. A systematic practice of these well-

known cultural methods will improve both the yield and

the quality of fann crops. In any kind of farming the

best results cannot come without proper attention to

these principles.

397. Seed-testing. — Whether the farmer raises or buys

his seed, it is almost sure to contain some impurities, such

as broken kernels, seed of other crops, dirt, chaff, and weed

seed. A mixture of varieties prevents marketing to best

advantage where it does not hinder in other ways, while

broken kernels, dirt, and chaff may cause poor crop stands,

thereby lowering yields and affording opportunity for

weeds to get started. Weed seeds introduce undesirable

plants into the field. These usually cause a decrease

in the desirability of the harvest as well as a decrease in

yield, to say nothing of the extra labor entailed in con-

trolling the pests. Noxious weeds new to the district

or to the farm are frequently introduced into fields, causing

358 The Principles of Agronomy

endless diflSeuIty and perhaps making Impossible the

profitable production of some crop. Russian thistle,

bindweed, quack-grass, perennial sow-thistle, Canada

thistle, and milkweed are a few weeds especially hard to

eradicate that may be thoughtlessly introduced in impure

seed.

In addition to impurities in the seed there may be some

that lack the power to germinate or lack the necessary

strength to send up vigorous plants. Since it is desir-

able to know what kind and how much impurity seed

contains, and its relative power to grow, it is essential

to test samples before sowing.

In order to do this, small quantities of seed from several

parts of the sack or bin should be mixed thoroughly and

divided into halves, .one of which should be repeatedly

mixed and divided until a representative sample small

enough to test is secured. With the help of hand forceps,

needles, and a hand lens a separation of the sample into

five piles may be made : (1) good seed, (2) dirt and chaff,

(3) other crop seed, (4) broken kernels, and (5) weed seed.

By carefully weighing the separates, the tester can deter-

mine the percentage of purity, and by comparing the

weed seed with samples in a collection, he can find out to

what weeds they belong. The next step is to test the

viability, or germinable power, of the pure seed. To do

this a plate half full of moist sand is covered with a piece

of white cloth or blotting paper, and 100 or 200 seeds are

counted out on it. After placing another plate on top

to prevent drying, the plates are set in a warm place. In

a few days the seeds that have germinated may be counted

and recorded. Repetition of the counting every day for

a short period will show the percentage of germination.

By referring to tables of purity and of germination stand-

ards, one may find out if the seed is worth planting.

Improvement of Crops 359

398. Reproduction. — A seed is the mature, fertilized

ovary of a plant and the connecting link between two

generations' of plants. The parent plant grew and

developed partly in order to produce seed that it might

leave another generation of similar plants. Flowers in

plants seem to be primarily for this purpose. A perfect

flower consists of calyx, corolla, stamens, and pistil, but

many plants have only the last two parts, which are the

important ones, since from them the seed develops.

Pollen from the stamens alights on the stigma of the

pistil and under favorable conditions sends a long tube

down the style to the ovule. The union of the pollen

and ovary causes a union of the male gamete in the

pollen with the female gamete in the ovule. This process,

known as fertilization, begins the life of the seed which,

when mature, consists of (1) a miniature plant or embryo

surrounded by (2) a quantity of stored-up food, both

of which are in turn inclosed in (3) a membranous cover-

ing called the hull. Since each seed is capable of be-

coming a plant, the number of descendants a parent

plant may have depends on the number of seeds it can

produce. This varies from a few hundred in the case of

some crops to a quarter of a million or more in the case

of large Russian thistles or tumbling mustard.

399. Variation. — Mere chance would cause some of

the many descendants to differ from others, but the law

of variation causes each individual to differ from every

other. Just as no two people are alike, no two plants

are alike. They differ in color, size, shape, rooting, flower-

ing, and in numerous other ways. Oats always bring forth

oats, but there are no two oat plants that do not differ.

One among several thousand will do best in particular

surroundings. It is upon this principle that both natural

and artificial selection depend.

360 The Principles of Agronomy

400. Natural selection. — Because some one plant out

of thousands is more fitted to survive in its particular

siUToundings, that one plant will grow most vigorously.

Now, if all the seeds from any one kind of plant grew,

this plant would soon fill the whole earth. Therefore,

in the end, not many more individuals can live next year

than do this year without crowding out others. Since

only a few of all the descendants of a plant can possibly

survive, those most fit live and the remaining ones die.

Thus nature constantly improves the wild plaints by

unending, relentless selection. For countless ages, only

the most fit of whole races have endured to rear descend-

ants, which in turn are culled out by ever increasingly

rigorous selection. The longer this weeding out of the

weakest continues, the better adapted the siu'vivors are

to cope with their enemies. All our bad weeds origi-

nated in the Old World where, for thousands of years,

they have been struggling for existence in cultivated

fields. This long, incessant struggle to retain foothold

has developed their means of survival.