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II. The Principle of Interactions in Soil Use

II. The Principle of Interactions in Soil Use

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I I3

Within his skills and with the facilities available to him, he tries to make

the soil as nearly ideal as practicable for the crops most likely to grow

well. Only a tiny fraction of the soils of the world produce well under

simple management that includes only clearing, plowing, seeding, and

harvesting. For most crops the farmer needs a stable soil that water, air,

and roots can penetrate deeply in order to have a large volume of soil

for storing water and plant nutrients and for releasing them to the roots

of the plants.

For each kind of soil, and the associated climate and length of day,

standards can be designed for the combinations of characteristics that

an arable soil should have for the most rewarding results. No soilmanagement practice or system is universally beneficial. A well-proved

system for one kind of soil may be harmful or perhaps wasteful on another

kind, even in an adjoining field.

Because the effect of any single soil characteristic depends on the host

of other characteristics in the combination that makes a soil of a certain

kind, we cannot make useful generalizations in terms of a single soil

characteristic or even of only three or four. Few useful statements about

soil management can be made about salty soils, hilly soils, clayey soils,

red soils, or the like.

Because of differences in clay minerals, some kinds of gently sloping

clayey soils are slowly permeable to water and have a high erosion

hazard under cultivation, whereas other kinds of clayey soils are so

permeable to water that crops can be grown without significant erosion

even on soils with 40 percent slope. (Fig. I).

Every productive hectare of arable soil in the world has at least four

basic conditions, appropriately related to one another and to the local

kind of soil. A balanced combination may have been arrived at over

years of trial-and-error or through planning with the aid of science. If

adequate practices for any one of the conditions are neglected, little can

be expected from the other practices. Some unique kinds of soil respond

well to only a very few combinations of practices; other kinds of soil

have a wider range of alternatives. The four basic conditions are:

1. The arable soil needs a balanced supply of plant nutrients for

acceptable yields. For the best results, at least some chemical fertilizers

are nearly always necessary to supplement the supply of one or more of

the many essential plant nutrients within the soils plus that contributed

by compost, manures, crop residues, and green manures. Thus the kinds

and amounts of fertilizers to use depend on the soil, other practices, and

expected costs and returns. Fertilizers are especially critical in areas of

high rainfall and leaching, all the way from the cool temperate regions

to the humid Tropics (lgnatieff and Page, 1958).



Recently some have overemphasized the critical role of fertilizers in

tropical countries in relation to the other inputs. That is, high yields on a

sustained basis do require considerable fertilizer, but fertilizer alone is

FIG. 1 . A strongly sloping, yet only slightly erodible excellent clayey soil used for

potatoes near Ootacamund, India. The trees are Eucalyptus. Pruned branches are used for

manufacturing a special oil. (These are examples of some of the best upland soils of the

Tropics -typical Reddish-Brown Latosols, likely Ustropepts in the new system of classification.)

not enough. Fertilizers are economically effective only i f ( a ) the correct

kinds and amounts are used for the local kind of soil and the crops to be

grown and ( b ) the practices needed to meet the other requirements for

good harvests are adopted at the same time.

2. A productive arable soil has adequate moisture in the rooting zone

when the plants need it, without the waterlogging that deprives the roots

of air. A good arable soil holds abundant water and lets the excess drain

on through. Few kinds of soil have a combination of characteristics and

associated climate for ideal water control. Some need shaping, diversions,

or terraces (bunds) for runoff control; some need irrigation; others need

drainage; and many need a combination of two or more of these practices.

Recently much emphasis, perhaps overemphasis, has been given to

irrigation. We must recall that by far the greatest amount of water used

by the crop plants of the world is that which falls as rain on the surface of



fields. Practices to conserve this water are normally cheaper than those

for irrigation. Nor will irrigation be successful unless a good job is done

of shaping the surface and of avoiding waterlogging and accumulation

of salts.

This is not to say that irrigation cannot be highly rewarding if a good

enough job is done to eliminate moisture deficiency as a limiting factor,

and if the other essential practices are also carried out. In a great many

regions with erratic rainfall, more can be had for the labor and capital

with improved runoff control.

3 . Success requires a variety of crop (or varieties of several crops in

rotation or in a mixed culture) adapted to the environment and with the

genetic potential to respond to the most favorable arable soil that it is

practicable to develop. Occasionally but not commonly, an improved

variety by itself can lead to significant increases in yield, at least for a

while. That is, a new crop variety placed in a primitive system may

result in a 2-fold increase; yet if combined with adequate fertilizers and

water control, it might lead to a 10-fold increase. Neither crop variety

nor fertilizer is any kind of panacea by itself.

4 . Arrangements are needed to protect plants (and animals for which

the crops may be grown) against diseases, insects, weeds, predatory

animals, and other hazards. The problem ofweeds, for example, commonly

becomes very difficult after clearing for continuous culture as compared

to primitive shifting cultivation, especially in the Tropics. With 3 to 4

years in crops, let us say, and 12 years of rejuvenating forest trees, the

biological cycles of insects, diseases, and weeds are interrupted, but if the

soils are used in open fields under permanent cultivation, much more

attention must be given to pest control.

5 . Supplementary practices. In addition to these basic and universal

sets of practices, some potentially arable soils can be used with heavy

investments for protection against the sea, mountain torrents, and floods.

From smaller investments some can be used with protection against high


We emphasize again: Each vital practice in the combination depends

on and supports the others. We can never be sure how much of a crop

yield can be attributed to fertilizer, how much to a new variety, or how

much to water control. Many interactions in farming are a bit obscure,

and unless we find them, we can be seriously misled. For example,

people have interviewed cultivators using fertilizer. Those cultivators

may get higher yields than others. But it is wrong to attribute all the

differences in yield to fertilizer or to any other single item under study.

Cultivators who take the trouble to use fertilizers usually carry out other





improved practices that help to make them effective. The same is true

of those who use a new variety or some other improved practice.

Besides the “pessimistic” or “scare” statements about the hopelessness

of the world food problem - “no new land,” “erosion,” “leached tropical

soils,” and so on, we have had overemphasis on fertilizer alone, on

irrigation alone, and recently on the new “miracle” varieties. Clearly

fertilizers and high-yielding varieties are essential parts of combinations

of practices suited to the local kinds of soil. So are water control and

plant protection. A failure of any one can make the others ineffective.

Perhaps it is only human to look for a single answer or slogan to promote increased farm production. The hopeless search results partly because people unfamiliar with farming may think that agriculture is very

simple. Nothing could be further from the truth (United Nations, 1963).


The principle of interactions also guides the working out of a good

system for an operating unit made up of fields of different sizes and kinds

of soil. The management system best for any one field of a farm depends

partly on the alternatives for use of other fields, especially in mixed

farming either with crops and livestock or with industrial crops and food


Soils that do not response economically to systems with cultivated

crops may support permanent or semipermanent forage, trees, palms, or

shrubs. Industrial or forage crops can be grown on some of these soils,

and food crops on those easily made arable. Commonly, sloping soils

unstable in cultivation can be changed gradually from natural forest

cover to rubber trees, coffee, cacao, or oil palms without exposing more

than narrow contour strips to the sun and rain, and these only for a short


Small areas too wet for normal crops can gradually be built up by

bedding with soil from the outside or from ditches between beds for crops

that can be sold or othenvide used within the farming enterprise (Fig. 2).

Thus, the measure of success is not simply what can be done on the

most productive soils but the production that can be had from the whole

land tract that makes a farm.


The same principle of interactions needs to be observed in planning

essential services for a village or rural community so that cultivators can

have available the materials and services for effective combinations of

soil management practices. If cultivators farm better, they must have



incentives; this means local markets with fair grading and prices. They

need appropriate tenure arrangements and opportunities for basic education, for learning technical skills, for credit, for industrial supplies, and

FIG.2. A cultivator and his family in Karala State, India, are bringing in soil material

from the outside to build a well-drained soil for coconut palms that give higher returns than

rain-fed rice. As the palms grow, the intervening areas are filled.

for technical assistance on special practices. As pointed out earlier, many

of these services are more economically supplied if costs are shared with

other economic enterprises. Each of these services influences the

effectiveness of the others and which of the alternative farming systems

is best for each cultivator.



Effective programs of technical assistance require some kind of country

planning. To an observer from abroad it may seem that many things

could and should be done in most newly developing countries. But the

local people cannot do everything themselves and also get the economy

going. Usually the total number of both professional people and skilled

technicians is small. If too many kinds of projects are attempted with

subsidies or grants from various sources, efforts are likely to get spread



too thin for the small corps of trained people to be effective. Since every

country gets its start toward economic growth out of agriculture, emphasis

needs to be placeti on farming and on the industries that serve farming

(Bauer, 1965).

1 . Combined Resource Use

Planning for economic growth should begin by taking advantage of the

combinations of resources and skills already available. The plan should

include early efforts for agricultural research, including soil surveys.

Appraisals will be needed of the resources of water, forests, and minerals

and of the skills of the population. In most of the less developed countries,

a large part of the population has skill in farming. Even though the farming may not be near the potential, we should not assume that cultivators

lack all basic skills for farming or that they are unable to take on new

ones fairly rapidly with good demonstrations and the incentives of good

prices and of local markets with fair grading. The goal in planning for

economic growth needs to be income to the people-money in their

pockets - rather than “monuments” -capital goods per se (Johnson,

1967). Then too, local communities need to be able to arrange necessary

training, credit, fertilizers and other chemicals, and adapted machines.

2. Education

Most writers have given great emphasis to education, perhaps with

some overemphasis on primary and university education and not nearly

enough emphasis on intermediate technical training in the local language.

Agricultural development and associated economic development require

large numbers of skilled people- machinists, electricians, truck drivers,

and the whole list.

Then too, many have encouraged bright young men and women in the

less developed countries to go to either Europe or North America for

their university education. This has not seemed to work well, partly because of an unhappy social gap between educated people able to attend

college and the mass of cultivators and laboring people. Also a young

man or woman taken out of his own society and placed for 4 to 7 years in

Europe or North America becomes adjusted to a quite different culture.

When he finishes, he really belongs to neither the new culture nor the

old. Back in his home country with the prestige of a Western degree, the

social gap between the graduate and his fellow citizens commonly is

further widened. The mass of simple people tend not to accept him, nor

can he easily communicate with them.

Comparable expenditures to help the less developed countries develop



their own colleges and training institutes for their young people are much

more productive to the economy. After graduates have completed their

training and demonstrated their ability to analyze problems and work well

in their trades or professions with the mass of people in their country,

tours and additional training in other countries are useful. As soon as

possible, such local training through the Ph.D. degree should be arranged

and should come before much study abroad. The work of the Rockefeller Foundation and the Government of India has demonstrated what

can be done.

In some countries scholarship standards and salary opportunities in

agriculture tend to be lower than in law, medicine, and literature. For

economic development additional emphasis needs to be given to training

scientists and engineers in agriculture, including both advisors in farming

and professional workers in related public and private services, because

agriculture is so vital for getting a start toward economic development.

3 . Research

The total effort in tropical agriculture must be greatly stepped up in

both basic and adaptive research (Moseman, 1964). Many of the existing

research institutes are working along narrow lines, even on a single

function or crop. The great need is for general research stations with good

staff in all lines, including the social sciences, soil surveys with accompanying laboratory work, and related field research. For results to be

effective in developing farming systems and broader agricultural systems,

people of many skills must work together and with cultivators to take full

advantage of the principle of interactions.

In research programming, special emphasis is needed on field and on

combined field and laboratory studies. Our knowledge of how tropical

plants and soils get their nitrogen is inadequate, for example. Many observers have reported good supplies that cannot be accounted for by

currently known mechanisms. If they were known, no doubt much greater

advantage could be taken of them. Similarly, more study of improving

supplies of calcium in many tropical soils is needed.

This is not to suggest that nothing can be done now. A great deal can

be done through soil surveys, exploratory studies of existing farming,

and field testing of promising new combinations of practices, including

fertilizers, based on principles already known from research and experience elsewhere in the world on similar kinds of soil.

4 . Industrial Sectors

Generally speaking, agriculture is most efficient in countries with a



growing industry. Yet the fact that capital accumulation to get industry

started comes mainly out of agriculture has been overlooked in some of

the newly developing countries. The lack of adequate rural statistics has

been another reason for neglecting the importance of agriculture as a

source of saving. Steel mills, great hydroelectric plants, huge dams for

irrigation, and the like are easy to count. Yet if most cultivators in a

newly developing country developed one-fifth of an acre or more of

greatly improved arable soils with runoff controlled, bought two or three

bags of the correct fertilizer for their soils, got improved seed, and bought

a duster for insecticides, the total investment would be large. If the advisory services were reasonably sound, this investment would lead at

once to increased farm production, income, and opportunities for savings.

And with more money, the many cultivators buy more, which further

boosts the economy.

Thus, we should argue that high emphasis be placed on investments for

transport, marketing, and the other industries that serve agriculture or

are developed with it. If these service industries can be properly organized, they also give income to people and return savings that can be

used later for still more basic industries. Then as industry develops and

furnishes more materials for farming, countries experience the usual

substitution of off-farm labor for direct farm labor.

5 . Public Versus Private Sector

Every country has some balance of economic activity in both the public

and the private sectors. Too far one way or the other may lead to inefficiency. Certainly the balance varies from country to country. Private

firms competing under a fair set of rules, honestly enforced by government, can lead to efficiency. Public agencies with leadership devoted to

the public interest can most effectively handle many kinds of essential

services. Yet either an entrenched private or public monopoly, without

fair competition and with indifferent management resorting to nepotism,

can lead to inefficiency and high cost for goods and services essential to

agricultural and economic development.

Decisions on these matters can be very important to farmers. If fertilizers and machines, for example, are too costly or of low quality, farmers

are severely handicapped in developing balanced systems of soil management for high yields and efficiency. Of course, what they can pay depends partly on prices they receive. In calculating benefits from fertilizer one should think not only of cost per kilogram of fertilizer in currency but also of cost in terms of kilograms of the farmers’ production,

be it rice or oil palm nuts. The incentive to use fertilizer on rice, for ex-



ample, is quite different if one cultivator can get 1 kg. of fertilizer for 1 kg.

of rice whereas another cultivator must give 6 kg. of rice for the same

fertilizer. If the methods for processing and marketing farm products are

unreasonably costly, farm prices are likely to be too low to give farmers

the incentives for full production. The same principles apply to costs for

credit and other essential services.

Thus, in country planning, decisions about how essential services are

organized and operated have a great deal to do with expansion of farming

and its efficiency and with progress toward a modern agricultural system

for the country.

6. Trade Relations

Trade relations have a strong influence on farm development. Especially in the early stages, many newly developing countries must depend a

great deal on farm products, such as tropical woods, tropical fruits, palm

nuts, rubber, fiber crops, and other industrial crops for a part of their

foreign exchange. Thus, we cannot think of effective agricultural development in terms of food alone.

In fact, some have gone to such extremes in this direction as to gauge

agricultural development only by international trade in grain -as if this

were equivalent to food. Actually people vary widely in the amount of

grain they eat, from none to a high percentage of their diet. Further, much

trade in grain and other foods takes place in rural villages where none of

it is counted. Much better statistics on all important kinds of food and

industrial crops, at least in sample villages, are urgently needed for

reasonable estimates of actual food production and consumption, and of

that available for trade in the general market.

Trade relations between the newly developing countries and the advanaced countries are highly important to both. The developing countries

need foreign exchange in order to buy equipment, instruments, and other

supplies necessary to get started toward improved agricultural systems.

In fact, many of the advanced countries need to search more carefully

for ways to expand their imports from the newly developing countries if

they are to move ahead in an orderly manner. Ultimately efforts toward

increasing trade are bound to benefit both groups of countries. These

trade relationships need continual study because of changing requirements and technological substitutions (Johnson, 1967).

7 . Finance and Taxation

Several of the less developed countries have traditional finance and

taxing arrangements that seriously handicap farming and discourage



investments in agriculture. Some have special export taxes on farm

products, so that the cultivators get considerably less than the prices on

the world markets. In some countries schemes may allow sales of certain

products only to a government monopoly at low prices; then the products

are sold at higher prices on the world market. This amounts to a tax on

farming. In a few less developed countries cultivators are handicapped

by being charged higher prices for local fertilizers or other materials

produced within the countries than the sale prices for export. This also

amounts to a special tax on farming.

Such unfair taxes or low local prices for farm products and high local

prices for materials and services are used in some countries to favor the

city population. In the end, this sort of practice hurts everyone by holding

back agricultural progress, which is the normal forerunner of general

economic development.

It is highly important to correct these handicaps- to recognize that

cultivators need fair prices and to replace unfair taxes on farming with

other sources of revenue. Where income taxes are difficult to enforce,

substantial sales taxes on imported luxury items would be paid by those

most able to pay, whether cultivators or urban dwellers.

Similarly cultivators should not be required to pay unreasonably high

rates for credit needed to make investments in machines, chemicals,

improved seeds, and the other inputs essential to modern management


Ill. Higher Production from Existing Arable Soils

Nearly one-half of the soils of the world that have good physical and

biological potential for farming are already in use. On these arable soils

yields could be considerably higher and the efficiency of producing them

could be greater. This is true for large areas in advanced countries,

whereas in many other parts of the world yields are only one-tenth to onehalf of those had by skilled farmers elsewhere on similar kinds of soil.

It commonly costs less to improve farming on arable soils in use than to

develop farming on new, unused potentially arable soils. First of all, the

cultivators are there and already know something about the farming of

their soils. Second, at least part of the essential infrastructure-roads,

markets, and the like-is in place.

Yet cultivators obtaining low yields on soils responsive to management may be handicapped in several ways, e.g., by inadequacy of education, transport, markets, and access to products of the industrial sector

of agriculture or by prices and taxes that discriminate against farm people.

Most cultivators are willing and able to work hard to support their



families, but returns in the market place may be so low that they have

little incentive to use added inputs for production beyond family needs.

As pointed out in the previous section, several practices must be

combined, in proper relationship to the local kind of soil and to one

another, for rewarding harvests in relation to inputs of labor, skill, and

materials. Because of the great contrasts among the many thousands of

kinds of soil and their associated crops, the “packages” of practices vary

widely from place to place, even between one kind of soil and another

within a small holding. Especially in tropical areas, more local research

is needed to learn how best to combine machines, chemicals, and other

products of the industrial sector of agriculture to have better farming

systems for the many kinds of tropical soils.


Soil surveys are essential for the full use of the results of research and

of experience related to soil management. For orderly use in technical

assistance, these results need to be reported and summarized by specific

kinds of soil. No one has yet found a reasonable alternative for assernbling knowledge about soils for application to the specific land tracts where

it applies.

1 . Operational Planning

For operational planning and technical assistance the maps in such

soil surveys must be in enough detail to show clearly the kinds of soil

in each important field and holding.

The degree of detail depends on the relative intensity of potential use,

the relative value per hectare of labor and other inputs, the complexity of

the pattern of unlike soils in the landscape, and their degrees of contrast.

Then too, where expensive structural works, such as those for water

control - runoff control, drainage, irrigation, or land shaping-are in

prospect, detailed soil mapping is required for satisfactory results without

waste. Soil surveys are essential for carrying out programs to consolidate

fragmented holdings: programs that are essential to effective water control and field design in millions of farm villages. Thus the scale for adequate soil mapping ranges from about 1 :50,000in areas with simple soil

patterns or only extensive uses to about 1 :8000 for highly intensive farming. (At and around the site of expensive structures, along planned highways, and for housing clusters, field mapping may need to be done at a

large scale, say 1:1000,where the pattern of soils is very complex.)

The soil map must also have plotted on it accurately the roads, streams,

houses, and other features that a user can see and that help him to locate

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