Chapter 28

Chapter 283,247 wordsPublic domain

THE ROTATION OF CROPS

SYSTEMS OF CROPPING

There are two methods or systems of cropping the soil:

The One Crop System, or the continuous cropping of the soil year after year with one kind of crop.

The Rotation of Crops or the selection of a given number of different crops and growing them in regular order.

The purpose of this chapter is to inquire into the effect of these two systems of cropping:

On the soil conditions necessary for the best growth and development of the crops.

On the market value of the crops.

On the increase of or the protection from injurious diseases and insects.

On the distribution of labor throughout the year.

On the caring for farm stock.

On the providing for home supplies.

This inquiry and the conclusion will be based on the following facts learned in the foregoing chapters.

Plant roots need for their growth and development (see Chapter II):

A mellow yet firm soil.

A moist soil.

A ventilated soil.

A warm soil.

A soil supplied with plant food.

Decaying organic matter or humus is one of the most important ingredients of our soils. Because:

It greatly influences soil texture and therefore the conditions necessary for root growth.

Its presence or absence greatly influences the attitude of soils toward water, the most important factor in plant growth. Its presence helps light, sandy soils to hold more water and to better pump water from below, while it helps close, heavy soils to better take in the water which falls on their surface. Its absence causes an opposite state of affairs.

The presence of organic matter checks excessive ventilation in too open, sandy soil by filling the pores, and improves poor ventilation in heavy clay soils by making them more open.

Humus, on account of its color, influences the heat absorbing powers of soils.

The organic matter is constantly undergoing more or less rapid decay unless the soil be perfectly dry or frozen solid. Stirring and cultivating the soil hasten this decay.

As the organic matter decays it adds available plant food to the soil, particularly nitrogen.

As it decays, it produces carbonic acid and other acids which are able to dissolve mineral plant food not soluble in pure water and thus render it available to plants.

Plants, although they require the same elements of plant food, take them in different amounts and different proportions.

Plants differ in the extent and depth of root growth and therefore take food from different parts of the soil. Some are surface feeders while others feed on the deeper soil.

Plants differ in their power to take plant food from the soil; some are weak feeders, and can use only the most available food; others are strong feeders, and can use tougher plant food.

Plants vary in the amount of heat they require to carry on their growth and development.

THE ONE CROP SYSTEM

We are now ready for the question. What effect has the continuous cultivation, year after year, of the same kind of crop on the soil conditions necessary to the best growth and development of that crop or any other crop? Suppose we take cotton for example.

How does cotton growing affect soil humus?

During the cultivation of cotton, the organic matter or humus of the soil decays in greater quantities than are added by the stalks and leaves of the crop. Therefore, cotton is a humus wasting crop, and the continuous cultivation of this crop tends to exhaust the supply of organic matter in the soil.

How does cotton growing affect soil texture?

Cotton growing wastes soil humus and therefore injures soil texture by making the lighter soils more loose and open, and the heavier soils more dense and compact.

How does cotton growing affect soil water?

By wasting humus cotton growing injures soil texture and so weakens the water holding and water pumping power of light soils and weakens the water absorbing power of heavy soils. Therefore the continuous cultivation of cotton weakens the power of the soil over water, that most important factor in crop growth.

How does cotton growing affect soil ventilation?

Continuous cotton culture, by wasting humus, injures texture and therefore injures soil ventilation, causing too much ventilation in the lighter soils and too little in heavier soils.

How does cotton culture affect plant food in the soil?

Continuous cotton growing wastes plant food:

Because it wastes organic matter which contains valuable plant food, particularly nitrogen.

Because by wasting organic matter it increases the leaching of the lighter soils and the surface washing of the heavier soils.

Because its roots occupy largely the upper soil and do not make use of much food from the lower soil.

Because it grows only during the warm part of the year and there is no crop on the land to check loss of plant food from leaching and surface wash during the winter.

Because it is a weak feeder of phosphoric acid, and can use only that which is in the most available form. In applying fertilizer to cotton it is necessary for best results to apply at least twice as much phosphoric acid as the crop can use, because it can use only that which is in the most available form and the remainder is left in the soil unused.

Continuous cotton culture then has an injurious effect on all the important soil conditions necessary to its best growth and development, and the result is a diminishing yield or an increasing cost in maintaining fertility by the use of fertilizer.

How does continuous cotton culture affect the economics of the farm?

The injury to the soil conditions necessary to root growth diminishes the yield and therefore increases the cost of production.

The poor soil conditions tend not only to diminish yield but also to diminish the quality of the crop, which tends to lower the price received for the cotton.

Keeping the land constantly in cotton tends to increase the insect enemies and the diseases of the crop.

The continuous growing of cotton does not permit the constant employment of one set of laborers throughout the year.

The continuous growing of cotton generally means that most of the farm goes into cotton. A small patch of corn is planted for the stock, which are apt to suffer from a lack of variety in food.

The same is true with reference to home supplies. Very few vegetables are grown for the table and there is little milk, butter or eggs for home use or exchange for groceries or drygoods at the store.

Thus we see that the continuous growing of cotton on the soil, year after year, has a bad effect on conditions necessary to its best growth and development and also on the economics of the farm.

These facts are true to a greater or less degree in the case of nearly all of the farm crops. The grain crops are often considered as humus makers because of the stubble turned under, but Professor Snyder, of Minnesota, found that five years' continuous culture of wheat resulted in an annual loss of 171 pounds of nitrogen per acre, of which only 24.5 was taken by the crop, the remaining 146.5 pounds were lost through a waste of organic matter.

THE ROTATION OF CROPS

Now, suppose that instead of growing cotton on the same soil year after year, we select four crops--cotton, corn, oats and cowpea--and grow them in regular order, a rotation practiced in some parts of the South.

We will divide the farm into three fields and number them 1, 2 and 3, and will plant these crops as indicated by the following diagrams:

Plan for planting.

Each of these crops occupies one-third of the farm each year, and yet the crop on each field changes each year so that no one kind of crop is grown on any field oftener than once in three years. The cotton is grown for market, the corn partly to sell, partly to feed, the oats to feed and the cowpeas to plow under. All cotton and corn refuse is plowed under.

What effect will such a system have on the conditions necessary for plant growth? Suppose we follow the crops on Field 1. Cotton, corn, and oats are humus wasting crops but the pea crop which is grown the third year is plowed under, and largely, if not entirely, remedies the loss by furnishing a new supply of organic matter, and the ill effects which we noticed would follow the loss of organic matter due to the continuous growing of cotton are avoided, soil texture is preserved, soil ventilation is not injured, and the power of the soil over water is preserved.

What is the effect on plant food in the soil?

Before answering this question let us see what amounts of plant foods these crops take out of the soil.

We will assume that the soil is a good loam at the start and will produce:

One bale of five hundred pounds of lint cotton per acre, sixty bushels shelled corn per acre, thirty bushels oats per acre, or two tons cowpea hay per acre.

Such a yield of crop would take from the soil the following amounts of plant food per acre:

+-----------+------------+------------ | | Phosphoric | | Nitrogen, | Acid, | Potash, | pounds. | pounds. | pounds. ----------------------+-----------+------------+--------- Cotton (whole plant) | 103 | 41 | 65 Corn (whole plant) | 84 | 26 | 61 Oats (whole plant) | 32 | 13 | 27 Cowpea | 78 | 23 | 66 ----------------------+-----------+------------+---------

Now suppose we sell the lint of the cotton, keeping all the rest of the plant, including the seed, on the farm and turning it back into the soil.

Of the corn suppose we sell one-half the grain and keep the other half and the fodder for use on the farm.

Suppose the oats be made into oat hay and be fed on the farm and the cowpeas be turned under.

Assuming that the cowpeas take half their nitrogen from the air.

This will mean that in the course of three years we take out of the soil of each acre in the crops:

Nitrogen. Phosphoric Acid. Potash. 258 pounds. 103 pounds. 219 pounds.

but we return to the soil in crop refuse and manure from the stock:

Nitrogen. Phosphoric Acid. Potash. 256 pounds. 87 pounds. 197 pounds.

This assumes that we have taken from the farm in products sold:

+-----------+------------+------------+ | Nitrogen. | Phosphoric | Potash. | | | Acid. | | ------------------|-----------|------------|------------| Cotton Lint | 2 | 1 | 2 | Corn | 28 | 12 | 10 | Animal products | 11 | 3 | 10 | +-----------+------------+------------+ Totals | 41 | 16 | 22 | ------------------+-----------+------------+------------+

The plant food charged to animal products is twenty per cent. of that in the grain and forage fed to the stock.

At the end of the three years the plant food account will balance up with:

Nitrogen a gain of 2 pounds. Phosphoric Acid a loss of 16 " Potash a loss of 22 "

This result is of course approximate. There will be some loss of nitrogen through leaching and denitrification. Some of the potash and phosphoric acid will be converted into unavailable forms. This can be made good by applying to the cotton a fertilizer containing twenty pounds of nitrogen, sixty pounds of phosphoric acid and twenty pounds of potash.

Additional nitrogen and organic matter can be grown to turn under by planting crimson clover in the cotton at the last working for a winter cover crop to be turned under for the corn, and by planting cowpeas or soy beans between the rows of corn.

If this is done it may not be necessary to add any nitrogen in the fertilizer, letting that supply only phosphoric acid and potash.

If commercial fertilizer is used on the cotton, it would be a good plan to apply the manure from the stock to the corn.

To follow our crop on Field 1 through the three years we will have, first, cotton drawing large amounts of plant food from the soil and diminishing the humus of the soil.

Growing a winter crop of crimson clover, turning back all the cotton refuse except the lint and oil, and applying the barn manure will furnish ample plant food for the corn and replenish the organic matter.

The corn is a rather stronger feeder of phosphoric acid than cotton and will be able to get sufficient from that left by the cotton.

The oats will be able to get a full ration after the corn, and the cowpeas will readily take care of themselves on the score of plant food and will put the soil in fine condition for cotton again.

The peas may be left on the ground to turn under in the spring at cotton planting time, or they may be plowed under in the early fall and a crimson clover or vetch cover crop planted, which will be plowed under for the cotton.

These same facts will be true of each of the three fields. The humus and, therefore, texture will be taken care of; ventilation, soil temperature and plant food will be controlled to advantage.

Each of the crops will be represented on the farm each year and the yields of each crop will be better than if grown continuously alone. The quality and therefore the market value will be greater. Insects and disease will be easier kept in control, and stock will be more economically furnished with a variety of foods.

BENEFITS DERIVED FROM ROTATION OF CROPS

Rotation of crops economizes the natural plant food of the soil and also that which is applied in the form of manure and fertilizer. This is because:

Crops take food from the soil in different amounts and different proportions.

Crops differ in their feeding powers.

Crops differ in the extent and depth to which they send their roots into the soil in search of food and water.

Crops differ in the time of year at which they make their best growths.

Rotation helps to maintain or improve the texture of the soil because the amount of humus in the soil is maintained or increased by turning under green manure and cover crops which should occur in every well-planned rotation.

Rotation helps to maintain or increase the plant food in the surface soil. When crops like cowpeas or clover which take mineral food from the subsoil and nitrogen from the air, are plowed under, they give up the plant food in their leaves, stems and upper roots to the surface soil, and thus help to maintain or increase fertility.

Rotation tends to protect crops from injurious insects and diseases. If one kind of crop is grown continuously on one piece of land the soil becomes infested with the insects and diseases which injure that particular crop. If the crop is changed, the insects and diseases find difficulty in adapting themselves to the change and consequently diminish in numbers.

Rotation helps to keep the soil free from weeds. "If the same kind of crop were grown year after year on the same field, the weeds which grow most readily along with that crop would soon take possession of the soil." For example, chick weed, dock, thistle, weeds peculiar to grain and grain crops tend to increase if the land is long occupied by these crops.

Rotation helps the farmer to make a more even distribution of labor throughout the year. This is because crops differ as to the time of year at which they are planted and harvested.

Rotation of crops enables the farmer to provide for his stock more economically. Live stock fares better on a variety of food, which is more cheaply secured by a system of rotation than otherwise.

THE TYPICAL ROTATION

A typical rotation for general farming should contain at least:

One money crop which is necessarily an exhaustive crop.

One manurial crop which is a soil enricher.

One feeding crop which diminishes fertility only a little.

One cleansing crop, a hoed or cultivated crop.

CONDITIONS WHICH MODIFY THE ROTATION

There are certain conditions which tend to modify the rotation or to influence the farmer in his choice of crops. They are as follows:

First of all the climate will set a limit on the number and varieties of crops from which a choice can be made for a given locality.

The kind of farming which he chooses to carry on, whether stock raising, grain farming, truck farming, or a combination of two or more of these, or others.

Kind of soil. Certain soils are best adapted to particular crops. For example, heavy soils are best suited to wheat, grass, clover, cabbages, etc. Light, sandy soils to early truck, certain grades of tobacco, etc.

The demand for crops and their market value.

Facilities for getting crops to market, good or bad country roads, railroads and water transportation.

The state of the land with respect to weeds, insect pests and plant diseases.

GENERAL RULES

A few general rules may be made use of in arranging the order of the crops in the rotation though they cannot always be strictly followed.

Crops that require the elements of plant food in the same proportion should not follow each other.

Deep-rooted crops should alternate with shallow-rooted crops.

Humus makers should alternate with humus wasters.

Every well arranged rotation should have at least one crop grown for its manurial effect on the soil, as a crop of cowpeas, or one of clover, to be turned under.

The objection often made to this last rule is that, aside from the increase in fertility, there is no direct return for the time, labor and seed, and the land brings no crop for a year. It is not necessary to use the entire crop for green manuring--a part of it may be used for hay or for pasture with little loss of the manurial value of the crop, provided the manure from that part of the crop taken off is returned and the part of the crop not removed is turned under.

LENGTH OF THE ROTATION

The length of the rotation may vary from a two-course or two crop rotation to one of several courses. Crimson clover may be alternated with corn, both crops being grown within a year.

A three-course rotation, popular in some parts of the country, is wheat, clover, and potatoes; potatoes being the money crop and cleansing crop, wheat a secondary money crop or feeding crop, and clover the manurial and feeding crop.

A popular four-course rotation is corn, potatoes or truck, small grain, clover; the potatoes being the chief money crop, corn the feeding crop, the small grain the secondary money or feeding crop, and clover the manurial and feeding crop.

On many New England farms near towns, hay and straw are the chief money crops. Here the rotation is grass two or more years, then a cleansing crop and a grain crop. A Canadian rotation is wheat, hay, pasture, oats, peas. A rotation for the South might be corn, crimson clover, cotton, crimson clover; this rotation covering a period of two years. A South Carolina rotation is oats, peas, cotton, corn--a three-year rotation. It might be improved as follows: Oats, peas, crimson clover, cotton, crimson clover, corn.