Chapter 24

FARM MANURES--CONCLUDED

GREEN-CROP MANURES

Green-crop manures are crops grown and plowed under for the purpose of improving the fertility of the soil.

The main object of turning these crops under is to furnish the soil with humus. Any crop may be used for this purpose.

By growing any of the class of crops called Legumes we may add to the soil not only humus but also nitrogen. Cowpeas, beans, clover, vetch and plants having foliage, flowers, seed pods and seeds like them are called Legumes.

Most of the farm plants take their nitrogen from the soil. This nitrogen is taken in the form of nitric acid and nitrogen salts dissolved in soil water. The legumes, however, are able to use the free nitrogen which forms four-fifths of the atmosphere. This they do not of their own power but through the aid of very minute plants called bacteria or nitrogen-fixing germs. These germs are so small that they cannot be seen without the use of a powerful microscope. It would take ten thousand average sized bacteria placed side by side to measure one inch.

These little germs make their homes in the roots of the legumes, causing the root to enlarge at certain points and form tubercles or nodules (Figs. 34 and 35).

Carefully dig up a root of clover, cowpea, soy bean or other legume and wash the soil from it. You will find numbers of the little tubercles or nodules. On the clover they will be about the size of a pin head or a little larger. On the soy bean they will be nearly as large as the beans. These nodules are filled with colonies or families of bacteria which take the free nitrogen from the air which penetrates the soil and give it over to the plant in return for house rent and starch or other food they may have taken from the plant.

In an experiment at Cornell University Agricultural Experiment Station, in 1896, clover seeds were sown August 1st, and the plants were dug November 4th, three months and four days after the seeds were sown. The clovers were then weighed and tested and the following results were obtained:

+---------------------------------------------- | NITROGEN IN AN ACRE OF CLOVERS. +---------------+----------------+------------- | Lbs. in tops. | Lbs. in roots. | Lbs., total. ----------------+---------------+----------------+------------- Crimson Clover | 125.28 | 30.66 | 155.94 Mammoth Clover | 67.57 | 78.39 | 145.96 Red Clover | 63.11 | 40.25 | 103.36 ----------------+---------------+----------------+-------------

A large part of the nitrogen found in these plants was undoubtedly taken by the roots from the soil air.

Besides adding humus and nitrogen to the soil the legumes, being mostly deep-rooted plants, are able to take from the subsoil food which is out of reach of other plants. This food is distributed throughout the plant and when the plant is plowed under the food is deposited in the upper soil for the use of shallow-rooted plants.

BENEFITS

The benefits derived from green crop manuring then are as follows:

We add to the soil organic matter or humus which is so helpful in bringing about the conditions necessary for root growth.

By using the legumes for our green manure crops we may supply the soil with nitrogen taken from the air.

We return to the surface soil not only the plant food taken from it but also plant food brought from the subsoil by the roots of the green manure plants.

CHARACTER OF BEST PLANTS FOR GREEN CROP MANURING

The plants best adapted to green crop manuring are deep-rooted, heavy-foliaged plants. Of these the legumes are by far the best, as they collect the free nitrogen from the air which other plants cannot do. This enables the farmer to grow nitrogen which is very expensive to buy.

THE TIME FOR GROWING GREEN MANURE CROPS

Green manure crops may be grown at any time that the soil is not occupied by other crops, provided other conditions are suitable. Land which is used for spring and summer crops often lies bare and idle during fall and winter. A hardy green manure crop planted after the summer crop is harvested will make considerable growth during the fall and early spring, and this can be plowed under for the use of the following summer crops. If there is a long interval of time during spring or summer when the land is bare, that is a good time for a green manure crop.

Green manure crops are often planted between the rows of other crops such as corn or cotton at the last working of the crop for the benefit of the crop which is to follow.

It is advisable to arrange for a green manure crop at least once in three or four years.

LEGUMINOUS GREEN MANURE CROPS

_Cowpea_. (Field pea, stock pea, black pea, black-eyed pea, clay pea, etc.) (Fig. 79.)

The cowpea is perhaps the most important leguminous plant grown for soil improvement in the South. It will grow anywhere south of the Ohio River and can be grown with fair success in many localities farther north.

It is a tender annual, that is, it is killed by frost and makes its entire growth from seed to seed in a single season. It should therefore be planted only during the spring and summer. This crop not only has power like the other legumes to take nitrogen from the air, but it is also a strong feeder, that is, it can feed upon mineral plant food in the soil that other plants are unable to make use of. For this reason it will grow on some of the poorest soils, and is a good plant with which to begin the improvement of very poor land. It is a deep-rooted plant. On the farm of the Hampton Normal and Agricultural Institute cowpea roots have been traced to the depth of sixty-one inches.

Cowpeas will grow on almost any land that is not too wet. From one and one-half to three bushels of seed are used per acre. These are sown broadcast and harrowed in or are planted in drills or furrows and cultivated a few times. Aside from its value as a green manure crop the cowpea is useful as food for man and the farm animals. The green pods are used as string beans or snaps. The ripened seeds are used as a food and the vines make good fodder for the farm animals.

"Experiments at the Louisiana Experiment Station show that one acre of cowpeas yielding 3,970.38 pounds of organic matter, turned under, gave to the soil 64.95 pounds of nitrogen, 20.39 pounds of phosphoric acid and 110.56 pounds of potash."--Farmer's Bulletin, 16 U.S. Dept. of Agriculture.

"It is now grown in all the States south of the Ohio River, and in 1899 there were planted nearly 800,000 acres to the crop. Basing our estimate on the amount of nitrogen stored in the soil by this crop, it is fair to say that fully fifteen million pounds of this valuable substance were collected and retained as a result of the planting of the cowpea alone. This at fifteen cents per pound (the market price of nitrogen) would be worth something more than $2,000,000 for nitrogen alone."--Year Book of the Department of Agriculture, 1902.

_The Clovers._--These are the most extensively grown plants for green manure purposes in the United States. They are deep-rooted, and are able to use mineral food that is too tough for other plants. They furnish large crops of hay or green forage and a good aftermath and sod to turn under as green manure, or the entire crop may be plowed under.

_Red Clover_ is the most widely planted (Fig. 80). It is a perennial plant and grows from the most northern States to the northern border of the Gulf States. It grows best on the loams and heavier soils well supplied with water, but not wet. It is sown broadcast at the rate of from ten to twenty pounds of seed per acre. In the North it is generally sown in the spring on fields of winter grain. In the South, September and October are recommended as the proper sowing times. It is the custom to let it grow two years, cutting it for hay and seed, and then to turn the aftermath and sod under.

_Mammoth Red Clover_, also called sapling clover and pea-vine clover, closely resembles the red clover, but is ranker in growth and matures two or three weeks later. It is better adapted to wet land than the red clover.

_Crimson Clover_, also called German clover and Italian clover, is a valuable green manure crop in the central and southern States east of the Mississippi. It is a hardy annual in that section and is generally sown from the last of July to the middle of October, either by itself or with cultivated crops at their last working. Fifteen and twenty pounds of seed are used to the acre. It makes a good growth during the fall and early winter and is in blossom and ready to cut or plow under in April or May. It grows at a season when the cowpea will not live. Crimson clover will grow on soils too light for other clovers.

The _Soy Bean_, also called soja bean and Japanese pea, is another leguminous crop used for green manuring (Fig. 81). It was introduced into this country from Japan and in some localities is quite extensively planted. It grows more upright than the cowpea and produces a large amount of stem and foliage which may be used for fodder or turned under for green manure The seeds are used for food for man and beast. The soy bean is planted and cared for in the same manner as the cowpea.

The _Canadian Field Pea_ is sometimes grown in the north as a green manure crop.

_White Sweet Clover_, white melitot or Bokhara clover, grows as a weed from New England to the Gulf of Mexico. In the Gulf States it is regarded as a valuable forage and green manure plant. One or two pecks of seed per acre are sown in January or February.

_Alfalfa_, or lucern, though grown more for a forage crop than for green manuring, should be mentioned here, for wherever grown and for whatever purpose, its effects on the soil are beneficial (Fig. 82). This plant requires a well prepared soil that is free from weeds. Twenty to twenty-five pounds of seed are planted per acre. In the north the seeding is generally done in the spring after danger of frost is past, as frost kills the young plants. In the South fall seeding is the custom in order to give the young plants a long start ahead of the spring weeds. One seeding if well cared for lasts for many years. Alfalfa is pastured or cut for hay, four to eight tons being the yield. Many fields run out in five or six years and the sod is plowed under. This plant sends its roots thirteen, sixteen, and even thirty feet into the soil after water and food, and when these roots decay they furnish the lower soil with organic matter and their passages serve as drains and ventilators in the soil. Alfalfa is grown extensively in the semi-arid regions of the country.

NON-LEGUMINOUS GREEN MANURE PLANTS

Among the non-leguminous green manure plants are rye, wheat, oats, mustard, rape, buckwheat. Of these the rye and buckwheat are most generally used, the rye being a winter crop and the other a warm weather plant. They are both strong feeders and can use tough plant food. They do not add new nitrogen to the soil though they furnish humus and prepare food for the weaker feeders which may follow them.