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IV. Green Manuring in Pedocals

IV. Green Manuring in Pedocals

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in the chernozem zone may be practiced to advantage, from the point

of view of supply of nutrients, providing that the moisture relationships

effect can be controlled satisfactorily. Benefits derived are in the category of chelating reactions, supplying phosphates (immobilized by the

heavy circulation of calcium in these soils) and iron, and perhaps

aluminum and manganese, made available in short supply by the wellknown local action reactions. The well-balanced ratio of nutrients supplied by the green manure and the impeded decomposition of native

humus are of positive significance.

With an abundance of moisture in this zone, decomposition of green

manure may cause a serious destruction of the stable native humus,

causing a drop in the organic matter constant and releasing toxic substances until such a time when this constant is re-established. It is

probable that this disturbance may be obviated by supplementing

mineral nitrogen when plowing under the green manure crop. An

example illustrating a number of the reactions involved in the condition just described may be found in the report by Plice (1950).

For 16 years green manures have been turned under in the spring

in a prairie soil of Oklahoma, vetch or winter peas on cotton and darso

(sorghum) land, and cowpeas or mung beans o n oat land. No information is given by Plice as to the time of plowing under the green manure

crop, the yield of tops and roots, the time of planting the case crops, or

the meteorological conditions. From climatological data on Oklahoma,

as reported in the Yearbook of Agriculture (1941), it is clear that at

Stillwater, where the experiments apparently have been conducted,

there is a concentration of rainfall in the spring. And this is the clue to

the lamentable results reported by Plice:

“Green manures have produced disappointing results. Sorghum and

cotton have not been benefited and the yields of oats crops have been

significantly reduced.” Plice states in the summary: “These findings

are mostly contrary to the general opinion on the ameliorating effects

of green manure in soils and are here interpreted to mean that the green

manure has had a degrading effect on the soil.”

Plice (1950) made an extensive study on the soils of the greenmanure and no-green-manure plots. His results are very enlightening

and instructive, but he makes no use of his findings to clarify his disappointing results. He found that “the green-manure soil is lower in

pH, available mineral nutrients, organic matter and nitrogen, bacterial

and fungal population, field moisture capacity, nitrifying power, macro

and micro aggregates, rate of water infiltration” green-manure soil has

“a higher plasticity, volume weight, weak-alkali soluble organic matter



and nitrogen, redox potential, ammonifying power, toxic humic substances, potential and exchangeable acidities, and wilting coefficient.”

The fact that the oats suffered more than the cotton is unquestionably due to their early time of planting. It had to follow soon after the

green-manure crop was plowed under. The oats were subjected to the

full impact of the disturbances described earlier. The sorghums and

cotton crops had a later planting date and by then the intensity of the

disturbances that had raised havoc with the oats had decreased. However, these disturbances had sufficient force to obviate the positive influences of supply of nutrient, etc., by green manuring and to encourage

the negative influences, and the net result was negative as far as yield

is concerned.

Nothing is mentioned by Plice as to the depth of plowing. Plowed

under to any depth, under conditions of the usually wet springs in that

area and in the presence of an initial high organic matter content, the

green manure crops could not but lose most of their positive influences

and exert in full force their negative influences on the crops following.

The excellent analytical data provided by Plice, when subjected to

review in the light of the reactions dictated by the zonality principle,

explain readily his “disappointing results” and challenging statement

that his “findings are mostly contrary to the general opinion.’’

If the green manure crops were removed (or dried and burned if

not used for animal feed) or chopped up and worked into the surface

3 to 4 inches of the soil, the results would have been reversed. An inkling to this probability is apparent from the statement that “oats was

superior on the non-green manure plots 75 per cent of the time.” Why

were not the results on the other 25 per cent of the time superior? A

venturous assumption is offered: during this period, the spring rainfall

must have been below normal and perhaps the top growth was not as

heavy, and the record should show that the sorghums and cotton crops

were much better with the green manure.

It may well be summarized that wherever the growing season is

long enough, green manure crops have their place in degraded chernozem, as well as in normal chernozem where spring precipitation

simulates the one described by Plice for the prairie soils of Oklahoma,

and if properly managed. If, however, the spring precipitation is low,

as is the case in large areas of the vast chernozem, the moisture effect

may preclude the favorable effects of green manuring. When heavy top

growth is plowed under it may introduce a cushion between the furrow

turned and the adjacent soil. The result is a drying out of the furrow

slice to the disadvantage of the germinating corn seedlings. Intake of



water under such conditions is impeded. This phenomenon has been

observed and reported in the literature. Methods of handling it generally consist of disking both prior to plowing under the crop and after.

This establishes contact of the plowed furrow with the soil body and its

moisture supply. In the chernozem zone this operation is more important than in the zones of laterization and podzolization, since the

paucity of precipitation dictates closer watch on conservation of


The better system of handling a green manure crop in the chernozem

zone, in the situation described, is to seed a mixture of a legume and

grass. This combination, even though not new, has been stressed in

recent years for the zone of chernozem in Russia and western Europe.

The papers of Chizhevskii and Losinskii (1953) and Burov (1953)

provide ample data to prove this point. The green manure crop should

be deprived of nutrients, whereby root growth would be enhanced and

top growth inhibited. Reducing the top growth to a minimum, less

moisture is used by the green manure crop and the danger of producing

the cushion referred to is eliminated. It is to be remembered that in the

chernozem zone, even with relatively high spring rains, the surface

soil dries faster than in the zone of podzolization, and every effort has

to be made to conserve moisture. If, for any reason, a heavy green

manure crop is produced, it should be removed and its fertilizing value,

in terms of NPK plus some magnesium, should be added as mineral

salts when plowed under.

I n view of the paucity of information on the practices of green

manuring in this zone, modifications of the expedients suggested in this

paper are to be guided by local experiences and interpreted in the light

of the specificity of the processes of soil formation as dictated by the

zonality principle. In this manner it should be possible to adjust the

steps in carrying out the green manuring operations favoring the positive effects and keeping down to a minimum the negative effects.

As we enter the areas of chernozem adjoining the zone of chestnutbrown and brown soils of the arid steppe, the moisture relationships

effect precludes green manuring. Sod in the rotation is used for a year

or two, with the top growth used for purposes other than plowing it


a. Burning the Straw in Grain Culture. In the areas where grain

culture prevails, there is the problem of handling the standing straw

after combining the grain. Whenever it is economical to remove the

straw from the fields, the minor problem of returning to the soil the

minerals carried away by the straw is similar to that of returning

minerals carried away by the grain. The loss of minerals caused by the



removal of the crop is usually compensated by returning to the soil

some animal manures and mineral fertilizers. Where removal of straw

is not economical, the difficulties engendered by plowing it under reintroduce the practice of burning it. Because of space limitation an

airing of the pros and cons of this practice has to be postponed. A few

remarks will suffice at this juncture.

When we have accepted the view that one of the most important

effects of green manuring is not the supply of organic matter but the

mobilization and release of plant nutrients, the burning of straw may be

evaluated in a more rational light. This controversial practice has in

its favor two points: ( I ) very little loss of nutrients is the result; (2)

the array of attendant disturbances are obviated. In addition the probability of nitrogen fixation should not be ruled out. This problem should

be dealt with by a specialized team of soil microbiologists well trained

in the genetic school of soil science, well grounded in the fundamental

sciences, supported by a staff of biochemists, physicists, pedologists, and

agronomists with similar backgrounds. The study should be made on a

meridianal scale. With the modern tool of isotope techniques, a study of

this kind offers an opportunity to uncover the elements of the specific

process of soil formation that are responsible for the positive and negative effects of nitrogen fixation associated with the expedients of green

manuring in the respective zonal soils.

In this connection one should ponder over the fact that by shredding

and chopping up organic matter and incorporating it into the surface 2 to 3 inches of the soil, the effects of burning are simulated. The

difficulty of this approach lies in the contradictions that arise from a

slow or speedy rate of decomposition of the organic matter, as discussed

earlier in this paper. This phase may become a part of the study


2. Soil T y p e s under Irrigation

These soil types preclude the practice of green manuring unless an

artificial supply of moisture is added. The geographic area of these

soils includes the chestnut and brown, desert-semidesert climatogenic

types of soil formation, and the climatogenetically subordinated or

subdued hydrogenic saline types of soil formation, namely, the solonchak, solonetz, and solodi. These soils differ from the senior member

of the pedocals, the chernozems, in a number of specific processes, of

which the root system is singled out for the purpose of illustrating the

manner in which green manuring may be effectively practiced.

The bulk of the root system in these soils is concentrated in the

relatively shallow A horizon. Tap roots or heavy branched roots do



enter the B and even the C horizons. Records to this effect are to be

found in investigations dealing with the problem of depth of penetration of roots. The shortage of moisture entering the A horizon in this

geographic area is not the only limiting aspect of moisture supply to

plants. The low moisture-holding capacity of the B horizon is probably

just as much of a hindrance as the total short supply of precipitation.

In the chernozem soils this horizon serves as a great reservoir of moisture. The low reservoir capacity of the soils under consideration is in

large measure determined by the high content of carbonates of calcium

in the B horizon and consequent low clay content. The relatively high

silt content of these soils and consequent low clay content impose a

low field capacity for moisture which restricts the development of an

extensive root system. It is because of this condition that the structure

of the soil in this area is not highly developed. Of course, the conditions

described become more acute as we move from the chestnut-brown

soils adjoining the chernozem towards the brown and gray semidesert

types of soil formation.

With the application of irrigation water, the more prolonged periods

of keeping up the optimum range of moisture for crop growth throughout the profile extend the feeding area for the root system and probably

influence favorably the capillary rise of water (the dangers of salinization are a subject by itself and are assumed at this juncture not to be


With the introduction of irrigation, green manuring may be utilized

to fullest extent, aiming at the most desirable effects, the mobilization

and supply of nutrients and a chance for improving the soil structure.

In short, the positive effects of green manuring, as discussed for the

pedalfers (zones of laterization and podzolization) , may readily be attained. Conditions of the system of agriculture followed in any particular section of this area may call for some modifications of expedients


The climatic conditions of this area afford better chances of utilizing

these effects. For one thing, the growing season is longer and with the

moisture factor under control the chances for success in these areas are

much greater.

With the changes in the rhizosphere induced by irrigation, the

reactions associated with the processes of humification and mineralization of the organic matter supplied by the roots and stubble of the green

manure crop (it is assumed that the top growth is not to be plowed

under and wasted) may over a period of years introduce a number of

changes in the profile. It is probable that the carbonate layer may be

pushed deeper, the clay content increased, the A horizon deepened, and

moisture-holding capacity increased. I n prospect is the encouragement



of some of the desirable attributes of the chernozem type of soil formation. Although these are speculative ideas, they lend themselves to

experimental verification and may be included in the scheme of the

meridianal study suggested in Section IV, la.

Green manuring in the areas of the saline type of soil formation is

practiced in a large measure for the purpose of increasing the buffer

capacity of the soil, thereby mitigating the negative effects of the higher

salt content usually present. To accomplish the high buffer effect, heavy

top growth is looked for to be plowed under. Very few reports are available on green manuring problems connected with soil management

practices on irrigated land in general and in particular with the problem

of disturbances accompanying the practice of plowing under heavy

top growth. Among the latest reports on this subject are the papers by

Lukashev ( 1950), who deals with the buffer capacity of irrigated soils,

and by Golubev (1952) on the decomposition of green manures in

irrigated chestnut-brown soils. Actually, these reports are nothing more

than results of empirical trials in the area under consideration.

It would seem that in order to attain the highest buffer capacity, the

green manure crop should be plowed under at a time when the moisture

content is low. Irrigation is to be withheld until the slow rate of decomposition has come to a standstill and desiccating reactions have fixed

the organic complexes and have increased their resistance to decomposition. Shallow mixing of this highly buffered humified organic matter would enhance the result desired.



Green manuring in the scheme of tilling the soil for bigger and

better crops has been appreciated for a long time, especially by progressive farmers whose experiences have contributed a great deal to

present the problems involved. The scientific agriculturists lagged

behind in interpreting gains made and in explaining failures, thereby

causing confusion and misunderstanding on the value of green manures.

The literature on this subject,' even to date, reflects helpless theoretical anchoring and poor comprehension of the mechanism involved

in the functions of green manuring. Misleading and frustrating have

been the attempts to duplicate results of one and the same practice in

different parts of the world.

The underlying cause of the confusion prevailing and lack of

progress in utilizing the potential benefits of green manuring practices

lies in the inappreciation of the zonality principle operating in nature.

It is shown that the pedologic approach, based on this principle, offers

an opportunity to clear the air of misapprehensions and provides rational interpretations of the true nature of reactions set off by green



manuring in the respective zonal soil types. With a clear understanding

of these reactions maximum benefits may be gained by following expedients tailored to fit the reciprocal reactions of the green manure

effects and those involved in the broad fundamental and specific soilforming processes.

The approach, stemming as it does from an application of the

natural laws governing the origin, formation, and geographic distribution of the soil as a body in nature, is sound and offers a chance of

coordinating the reciprocal reactions mentioned and of advancing the

benefits of green manuring.

It should be clear that deductions made for the expedients suggested

are based in some measure on experiments designed empirically for

other purposes. This circumstance may call for some modifications of

procedures and perhaps some experiments designed for that purpose.

Each zonal soil with its characteristic pedologic features has its own

mode of reactions to one or the other procedure. While most of these

reactions may be theoretically anticipated, some experiments to prove

the theories and ideas are in order. To this end a meridianal type of

experiment is suggested.

It is felt that we have not exploited the full potential of benefits

that can be obtained from green manuring for better and bigger crops.


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Plant Introduction as a Federal Service to Agriculture


U . S. Department of Agriculture, Beltsuille, Maryland



I. Preface . . . . . . . . . . . . . . .

11. Federal Participation in Plant Introduction . . . .

111. The Section of Plant Introduction and Its Organization

1. Plant Introduction

. . . . . . . . .

. . . . .


. . . . . . 190

. . . . . . 191

. . . . . . 192

a. Plant Procurement and Exploration . . . . . . . . . 192

b. Inspection House

. . . . . . . . . . . . . . 195

c. Quarantine

. . . . . . . . . . . . . . .

2. Propagation, Testing, and Distribution of Plant Introductions . .

a. Federal Plant Introduction Gardens . . . . . . . .

i. The Glenn Dale, Maryland, Plant Introduction Garden

ii. The Barbour Lathrop Plant Introduction Garden . .

iii. The Coconut Grove, Florida, Plant Introduction Garden

iv. The Chico, California, Plant Introduction Garden. .

b. State-Federal Cooperative Plant Introduction Stations . . .

IV. Benefits Resulting from Plant Introduction in the United States

. .




. 200

. 200













Long before the beginning of any systematic agriculture, prehistoric

man practiced a kind of unorganized plant exploration. As a wandering

fisher-hunter and food-gatherer he was forced to explore daily in order

to satisfy the primary and ever-present urge of hunger. With the establishment of primitive agriculture came the first true introductions of

plants-from the wild into man’s garden plots. Although the culture

of plants permitted a more sedentary existence, man did not entirely

cease his wanderings. The pressures of civilizations made him also a

colonizer. With him went his plants. The success of his plant introductions has been amazing and is typified by such important crops as

wheat, potato, coffee, and rubber, the centers of production of all of

which are now far removed from the native homeland of the parent


The history of plant introduction on this continent, as elsewhere,

started with the wanderings of aborigines who brought in what we commonly think of as “native crops”-maize, pumpkin, squash, bean, and



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

the like-from

tropical areas to the south. Not a single agronomic

species and no truly major crop plant originated in land now included

within the geographical borders of the United States. All except such

indigenous plants as the sunflower, blueberry, pecan, and cranberry

came from foreign lands. Even these indigenous plants required introduction from our fields or woods to our garden plots.

From domestic and foreign germ plasm, strains and varieties have

been selected or bred to fit the needs of our environment. The need for

plant introduction is a continual one. This is so because new diseases,

such as internal cork of sweet potatoes and tristeza in citrus or new

strains of old diseases, exemplified by the virulent 15b strain of wheat

rust, are continually appearing. The disastrous havoc of such plant diseases alone makes it imperative that our agronomists be constantly supplied with possibly resistant materials for trial, and that reservoirs of

basic plant material be maintained to supply the needs of our plant


In the early days, following the discovery of the Americas, colonists,

adventurers, and explorers brought with them seeds and plants from

the Old World. Plants from other parts of the New World were also

brought in, the potato being an important example. These plants became established and spread in the rapidly developing colonies.

As settled community life followed the rough pioneering days in

the colonies and homes followed homesteads, more and more attention

was devoted to bringing over from the Old World the best of fruit trees,

ornamental and flowering plants, shade trees, and food and fiber crops.

Many important collections, the influence of which was far-reaching,

were built up in these early years. At the same time there was tremendous interest on the part of the Old World gardeners in the new species

and types of plants to be found in America. Extensive collecting activities were conducted and immense quantities of plant material were

sent to Europe.





With the organization of an independent government in the

colonies, pressing problems of a political nature occupied the minds of

officials almost exclusively in the early years. Individual officials recognized the importance of plant introduction, but governmental recognition was much slower. I n 1827 President John Quincy Adams directed

all American consuls to forward to Washington rare plants and seed for

distribution. Twelve years later, in 1839, Congress passed its first appropriation for a g r i c u l t u r e a sum of $1 ,000-to be used primarily in collecting and distributing seed. This undertaking was then under the

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IV. Green Manuring in Pedocals

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