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IV. Benefits Resulting from Plant Introduction in the United States

IV. Benefits Resulting from Plant Introduction in the United States

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210



W. H. HODGE A N D C. 0. E R L A N S O N



about $50,000. The new industry they helped to found in this country

is now worth more than a billion dollars a year. Taxes paid by producers of this crop alone have repaid many times the total cost of all

plant introduction work since its formal inception in 1898. But soybeans

are not the whole story. There are the alfalfas (Medicago satiua L.)LADAK from India, Hairy Peruvian, and Creeping alfalfa from Turkey;

all the clovers (Trifolium spp.), some dozen or more; kudzu (Pueraria

Zobata ( Willd.) Ohwi) ; cowpeas (Vigna sinensis (L.) Savi) ; velvet

beans (StizoZobium deeringianum Bort) ; crotalarias; vetches (Vicia

spp.) ; and lespedeza. All our Korean lespedeza (Lespedeza stipulacea

Maxim.) came from a handful of seed collected in 1919 by a plant explorer in Korea. That handful of seed has mushroomed into a $120,000,000 a year crop.

From the standpoint of cotton the most outstanding find of plant exploration was ACALA, the germ plasm of which has contributed to a series of superior, drought-resistant, big-boll cottons with an excellent,

quality staple. Found over 30 years ago in southern Mexico as a dooryard plant in a hamlet from which it derives its name, ACALA cotton,

in one or more of its selections, has subsequently become the most important cotton in the American Southwest. California growers alone

pocket millions of dollars annually from this fabulous plant.

Horticulturists have long recognized the value of plant introductions

and down through the years have been supplied with a rich heritage of

plant germ plasm from abroad. Scores of varieties of beans, cabbages,

carrots, lettuce, onions, peas, peppers, pumpkins and squashes, radishes,

maize, and the like represent either direct plant introductions or firstgeneration selections. In these days of constant warfare against disease,

present-day vegetable breeders are looking more and more to related

wild species for use as parental material in vegetable improvement programs. The so-called Irish potato, wholly American in origin, is in itself

a good example. Since 1932, 56 new potato varieties have been released

in this country by breeders, and all but one can boast of foreign introductions in their pedigrees. What is more, selections of the wild potato

species of Mexico and South America are showing up as a source of

valuable genes. For example, Solanum acaule Bitt. selections, immune

from X virus, have demonstrated that they can withstand temperatures

down to 23O F.; S. antipovichii Buk. and S. chacoense Bitt. are immune

from Y virus; and many introductions of S. demissum Lindl. carry late

blight resistance. The same thing can be said of the tomato, wild cousin

species of which from Peru have supplied resistant factors for such serious troubles as fusarium wilt and root-knot nematode.

I n the field of tree crops results do not appear so soon because of



PLANT INTRODUCTION



211



the slow growth of such plants. Yet even here examples of the contribution of the federal plant introduction program are legion. The Washington navel orange, introduced from Bahia, Brazil, is the basis of one

of California’s important agricultural industries. Among other fruits introduced mention must be made of the avocado, date, lychee, Quetta

nectarine, Meyer lemon, Geneva apricot, Shalil and Yunnan peaches,

and Methley plum. T o this galaxy of trees should be added such items

as the Chinese hairy chestnut (Castanea mollissima Blume) , pistachio,

and tung.

Of secondary importance in our agriculture, ornamental plants have

always been overshadowed by their more important economic cousins

iii the program of plant introduction. Those that are woody also require

long-term evaluation, as demonstrated by the fact that only in 1953

could a report be issued recommending for the northern Great Plains a

series of several dozen hardy trees and shrubs collected some 40 years

earlier by our explorers in northern China and Japan. That explorers

have not entirely overlooked ornamentals has already been shown in

the galaxy of showy tropical and subtropical woody plants which have

emanated from the plant introduction garden at Coconut Grove to enrich the gardens of Florida and California. But there are others too:

the famed Japanese cherries of Washington, D. C.; the Chinese elm

(Ulmus paruifolia Jacq.) j Rosa xanthina Lindl., which has been a principal gene source of hardiness and color in our modern yellow tea rose;

Zlex cornuta Lindl., the Chinese holly, and its striking compact horticultural variety rotunda. Most recent contribution of the Section in the

field of ornamentals is the fine series of Glenn Dale hybrid azaleas, the

result of a breeding program in which were incorporated the genes of a

number of plant introductions.

The illustrations given represent but a few of the host of successful introductions that have been made since 1898, when the plant

introduction activities of the Department of Agriculture were formally

organized. They indicate how indispensable is sustained plant introduction work to the dynamic agricultural economy of our nation.



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The Enigma of Soil Nitrogen Balance Sheets

F. E . ALLISON

U. S. Department



of



Agriculture, Beltsuille. Maryland

CONTENTS



Page

I. Introduction . . . . . . . . . . . .

. . . . . 213

I1. Nitrogen Balance Sheet for the Cropped Soils of the United States . . 214

I11. Lysimeter Experiments . . . . . . . . . . . . . . . 216

1. Experiments at Ithaca, New York

. . . . . . . . . . 217

2. Experiments at Geneva, New York . . . . . . . . . . 219

3 . Experiments at Windsor. Connecticut . . . . . . . . . 220

4 . Experiments at Knoxville. Tennessee . . . . . . . . . 222

5 . Experiments at Riverside. California . . . . . . . . . . 223

6. General Remarks . . . . . . . . . . . . . . . 224

IV. Field Experiments . . . . . . . . . . . . . . . . 225

1. Experiments at Rothamsted. England

. . . . . . . . . 225

. . . . 226

2. Cylinder Experiments at New Brunswick. New Jersey

3. Miscellaneous Experiments . . . . . . . . . . . . 228

V . Greenhouse Experiments . . . . . . . . . . . . . . . 232

1. Experiments at Beltsville. Maryland . . . . . . . . . . 232

2. Experiments at Woburn Experimental Station. England . . . . 234

VI . Losses of Nitrogen by Volatilization . . . . . . . . . . . 235

1 . Losses as Ammonia . . . . . . . . . . . . . . . 235

2. Losses as Nitric Oxide by Chemical Reaction . . . . . . . 236

3. Losses as Nitrogen Gas by Chemical Reaction . . . . . . . 236

4. Losses as Nitrous Oxide and Nitrogen Gas by Bacterial Denitrification . . . . . . . . . . . . . . . . . . .

238

5 . Losses as Organic Substances from Plants . . . . . . . . 239

6. Practical Importance . . . . . . . . . . . . . . 239

VII . Gains of Nitrogen from the Air by Means Other than Legumes . . . 24.0

. . . . 241

1. Some Reported Nitrogen Gains under Field Conditions

2. The Organisms Involved . . . . . . . . . . . . . 242

3. Nonbiological Nitrogen Gains

. . . . . . . . . . . 244

4. Practical Importance-A General Statement . . . . . . . 246

VIII . Concluding Statement

. . . . . . . . . . . . . . . 246

References . . . . . . . . . . . . . . . . . . . 247



I . INTRODUCTION

During the past fifty or more years. many attempts have been made

to draw up nitrogen balance sheets for both cropped and uncropped

213



214



F. E. ALLISON



soils. In general, these attempts have met with only mediocre success

because quantitative data are usually not available for some of the items

that enter into the calculations.

On the side of income, accurate values for additions in the forms of

rainfall, irrigation water, seeds, fertilizers, and manures are usually

available. However, if legumes are grown, there are difficulties. The

quantity of nitrogen supplied from the air by rhizobia is not likely to

be known accurately under field conditions but can, of course, be determined under special controlled conditions. Or the experimenter may

avoid the problem by growing only nonlegumes. With regard to nonsymbiotic fixation, little is known about the quantities supplied under

field conditions because they are commonly too small to be measured.

Furthermore, any gains may be more than off set by unaccounted-for

losses.

On the expenditure side of the balance sheet, accurate values for

the nitrogen removed in harvested crops and in animals are commonly

available. As for wind and water erosion, these are usually of only

minor importance in carefully planned field studies. Leaching, however, presents a major problem. Seldom is it known what values to assign to this source of loss, and there seems to be a wide divergence of

opinion among agronomists as to whether such losses are likely to be

large or small.

After the balance sheet has been drawn up, income and outgo seldom balance, even though account has been made of all known soil

nitrogen gains and losses. Usually all of the nitrogen that went into

the system has not been recovered. It is assumed that some of it has

volatilized. Is this true, and, if so, how is it lost and in what quantity?

Only on rare occasions does income exceed outgo, if all of the nitrogen

added by legumes is excluded. This failure of nitrogen balance sheets

to balance constitutes the enigma of this discussion. I n a broad sense,

all items that enter into the nitrogen balance sheet are involved; in

other words, there are several enigmas. The present discussion will,

however, deal primarily with losses by leaching and volatilization, and

with gains of soil nitrogen from the air through channels other than

legumes. Such a discussion of nitrogen balance sheets should help to

explain why recoveries of nitrogen in the crop are often only 50 per

cent of that added as fertilizer.



11. NITROGEN

BALANCESHEETFOR THE CROPPEDSOILS

OF THE UNITED

STATES

When the subject of nitrogen balance sheets is mentioned, the one

published at New Jersey by Lipman and Conybeare (1936) imme-



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