Part 2

Sweet clover thrives on the adobe and granitic soils of the Pacific coast; upon the gumbo, hardpan, prairie, and sandy soils of the western North-Central States; and upon the heavy clay, loam, limestone, and sandy soils of the South and East. In fact, it has been grown successfully on all the principal soil types of the United States where the soils were not acid and were well inoculated. It grows luxuriantly on the Selma chalk (rotten-limestone) soils of Alabama and upon soils rich in calcium carbonate in many parts of the country where the lack of nitrogen and humus has caused large numbers of farms to be abandoned. The plants thrive on newly exposed heavy clay soils and upon steep embankments where little else will grow. Sweet clover is more tolerant of poor drainage, overflow, and seepage conditions than alfalfa. In irrigated sections, especially where the reservoir system is in use, large bodies of land are likely to become useless for the growth of alfalfa because of the rising of the water table. On such areas sweet clover will make a vigorous growth. However, maximum growth is to be expected only on well-drained soil.

Sweet clover will do well on many soils which are not fertile enough to grow red clover or alfalfa, and it is on these soils that it will prove most valuable. Like many other plants, it makes its best growth on fertile soils rich in calcium carbonate, although it will make sufficient growth on poor soils which are not acid to warrant planting it on them. Many hilly pastures may profitably be seeded to sweet clover. It will not only make a valuable addition to the forage of these pastures but will improve the soil so that grasses will grow more abundantly. Some of the best pastures in the Middle West are composed of bluegrass, timothy, and sweet clover.

RESISTANCE TO ALKALI.

Sweet clover grows successfully on soils in the West which apparently are too alkaline for grains or alfalfa. The Wyoming Agricultural Experiment Station reports that it has obtained good yields of sweet clover on seepage land which is so strongly alkaline that no other plants except some of the native grasses will survive, while the California Agricultural Experiment Station found that sweet clover will withstand alkali to a remarkable degree. Prof. F. S. Harris, agronomist of the Utah Agricultural Experiment Station at Logan, claims that it is one of the most alkali-resistant crops grown in Utah, and that in and 1913 and 1914 quite an industry developed in some parts of that State in growing sweet clover for hay and seed on land too alkaline for other crops.

In reply to a circular letter on the culture of sweet clover, approximately 100 county agents and extensive growers of this crop located in many parts of the West state that this plant is one of the most alkali-resistant plants grown in their respective districts. In Crook County, Oreg., a good stand was obtained from April seeding in 1915 on a 20-acre demonstration field of sandy loam bottom land so strongly alkaline from black alkali that only salt grass was growing on it before it was planted to sweet clover. This field pastured from 18 to 28 head of calves, cows, and horses from June 1 to October 1 without being irrigated. Sweet clover generally will grow on soils where salt grass[6] will survive, and it is very much superior to this grass as pasture. After the drainage of water-logged land on which there is a surface accumulation of alkali, it is the common practice in parts of Utah to grow sweet clover for several years before planting alfalfa. It is often stated that alkali land will grow less tolerant crops after sweet clover has been grown on it for a few years. The long roots will open up the subsoil and cause better drainage, thereby affording an excellent means for removing the salts from the soil, as they are readily soluble in water.

[6] _Distichlis spicata_.

NEED OF LIME ON ACID SOILS.

Sweet clover, like many other legumes, requires a soil containing an abundance of limestone if a maximum growth is to be expected. Throughout the world it makes a luxuriant growth only on calcareous soils. On the black prairie limestone soils of Alabama and Mississippi it grows luxuriantly, although in this region it is very seldom found on the outcroppings of red clay, which are acid. The distribution corresponds sharply with the line of demarcation between the black prairie soils and other soil types. In some places sweet clover makes a vigorous growth on the Selma chalk (rotten-limestone) soils, while none is to be found on red post-oak clay but a few yards away; yet sweet clover will grow on the red post-oak clay after the soil has received an application of lime. It will thrive on the bald lime-rock spots and rotten-limestone hills of Mississippi, which are so barren that practically no other plants will survive. Thus it appears that lime is essential for the maximum growth of sweet clover in this Region.

The reason for the exceptional growth of sweet clover in north-central Kentucky is undoubtedly the fact that these soils contain an abundant supply of limestone. The Kentucky Agricultural Experiment Station states that this area is the only portion of the State where sweet clover is being grown with general success without applying lime.

Soils on which sweet clover is aggressive are almost invariably alkaline or but slightly acid. This plant is often found in valleys of streams in localities where the soils are supposedly acid, but such streams generally have their origin in limestone areas or flow through limestone regions, and calcium carbonate is thus deposited in these valleys during flood periods with the sedimentary deposits from flood waters. Sweet clover often appears in deep cuts along highways or railroads in localities where the soil is known to be acid and where sweet clover has not previously grown. In many of these cuts the acid soil has been removed and neutral or alkaline subsoil exposed, or limestone has been used in ballasting or road making and the dust has blown on the exposed soil. It is a very common occurrence to find sweet clover making an abundant growth along macadamized roads from which the wind has scattered the finely pulverized limestone.

An application of burnt lime or finely ground limestone has made the difference between success and failure in most experiments which have thus far been conducted on decidedly acid soils. (Fig. 7.)

A number of sweet-clover experiments were performed on acid soils and on adjacent plats or fields of the same type of soil that had received applications of limestone varying from 1 to 4 tons to the acre. There was a marked difference in the stands obtained and in the growth of the plants on the limed and unlimed areas. In some cases the difference in growth was so marked that the last round of the lime spreader could be distinguished at some distance from the plats. The stands were much heavier on the limed areas and the plants made from two to three times more growth than those on the unlimed plats. Yields of hay were doubled on soils that received only sufficient limestone to neutralize the acids in the surface soil, although the yields were further increased when more limestone was added.

Mr. W. E. Watkins, county agent of Allen County, Kans., made counts of the number of plants which winterkilled during the winter of 1914-15 on given areas of limed and unlimed soil. It was found that from 15 to 35 per cent more plants winterkilled on the unlimed soil than on the limed areas. That portion of the unlimed field on which the fewest plants winterkilled was found to have the lowest lime requirement. On the unlimed areas with a low lime requirement 15 per cent more plants winterkilled than on the limed areas; on those with a high lime requirement the increase in winterkilling was 33 per cent. In the fall of 1914 the hay cut from the limed areas exceeded that from the areas with a low lime requirement by 600 pounds per acre and exceeded that from the areas of high lime requirement by 4,000 pounds per acre. In July, 1915, the increase in hay yield on the limed areas over that from the areas with a low and with a high lime requirement was 2,300 and 9,400 pounds per acre, respectively. The area of high lime requirement returned a small yield in 1914 and no hay in 1915.

In spite of the fact that sweet clover is as sensitive to soil acidity as red clover or alfalfa, a large percentage of the acreage thus far seeded in the eastern half of the United States has been composed of acid soils, and this soil acidity undoubtedly is responsible for a very large percentage of the failures with sweet clover in this section. Where sweet clover is to be sown on acid soils a sufficient quantity of lime should first be applied to at least neutralize the fields in the soil to a depth of 6 inches. An application of 1 ton of burnt lime or 2 tons of finely ground limestone will usually be sufficient for this purpose.

Fields have been noted where sweet clover was making a fair growth on apparently acid soils. Such fields usually are rich in humus or phosphorus and are exceptional cases rather than the rule.

Soil types which have slightly acid surface soils and alkaline subsoils will grow sweet clover successfully, provided the acid soil is not more than 6 to 12 inches in depth.

FERTILIZERS.

Owing to the fact that sweet clover thrives on the barren Selma chalk (rotten-limestone) hills of Alabama and Mississippi and grows abundantly on worn-out, abandoned land in north-central Kentucky, it is often assumed that it will grow on soils too depleted in plant food to produce other crops. These regions represent soils which have become exhausted primarily in nitrogen and humus as the result of continuous cropping with nonleguminous plants. Some of these soils contain sufficient phosphorus and potassium for fair crop production, although this supply may be in such a condition that it will not become available fast enough to supply the needs of most crops. Sweet clover, like all legumes, has the power to extract nitrogen from the atmosphere, and on account of its extensive root system it is able to obtain phosphorus and potassium from a larger area than most plants. The large roots not only add a quantity of humus and nitrogen to the soil but they also open it up to a considerable depth, thus providing better aeration and improving its physical condition. Improved physical condition causes the bacterial flora to increase and thereby indirectly causes a larger quantity of unavailable phosphorus and potassium to be made available for plant use.

On soils which are known to be low in phosphorus or potassium an application of fertilizer containing the necessary element should be made when sweet clover is sown without a nurse crop. However, when it is sown with a nurse crop or in the late summer or early fall on grain stubble, the residues left in the soil from fertilizers applied to the nurse crop will, under ordinary conditions, be sufficient for the plants. That sweet clover will respond readily to applications of phosphorus on soils low in this element has been well demonstrated by the farmers of Livingston County, Ill. In this county finely ground rock phosphate was applied to a portion of a number of fields at the rate of 1,500 to 2,000 pounds per acre. The phosphate was thoroughly incorporated with the soil just before seeding oats and sweet clover. In the growth of sweet clover there was a marked difference the following year between the treated and untreated portions of the fields. Those portions of the fields which received an application of phosphate not only contained many more plants on a given area, but the vigor and growth of the plants were most marked. On June 1 the plants on the treated areas were 12 to 15 inches taller than those on the untreated parts of the fields. This difference in the thickness of stand and the height of plants was so striking that the last round of the phosphate spreader was plainly distinguishable.

Yields of sweet-clover hay have been increased as much as 2 tons per acre from applications of barnyard manure. Such an increased yield would be equal approximately to 8 tons of green-manure. Some people may consider it poor farm practice to apply manure to such crops as sweet clover, but it is very probable that the cumulative effect of the increased yields of the following crops, especially on soils low in organic matter, will be greater than if the manure is applied to other crops. Heavy applications of manure to the preceding crop should also greatly benefit sweet clover.

USE OF A NURSE CROP.

If sweet clover is to become an important crop throughout the North-Central States it must necessarily be seeded with grain. Good success has been obtained by seeding sweet clover in the spring on winter grain or with spring grain on soil that was inoculated and not acid. Seed may be broadcasted in the early spring on winter grain when the ground is in a honeycombed condition, or it may be sown later when the ground may be cultivated. A large acreage of sweet clover is sown in the western North-Central States and in Illinois in the spring with oats, barley, or wheat as a nurse crop. Early varieties of oats and spring wheat have given somewhat better results in portions of the Northwest than barley. In Illinois oats are used almost entirely. Only a few fields were noted where flax had been used as a nurse crop, but in these fields it was successful. In wet seasons the sweet clover may make a growth sufficiently large to interfere seriously with harvesting the flax. On this account this combination should be tested thoroughly in an experimental way before being recommended for general field practice.

In those sections of the country where the moisture supply is limited, sweet clover should be sown without a nurse crop. Failure to obtain a stand is more likely to occur when the seed is sown with grain than when it is sown alone, because during dry weather, which is likely to occur when the grain is maturing, the supply of moisture in the soil is apt to be insufficient for both crops. When this condition prevails the clover will suffer badly and in some cases be killed. When sweet clover is sown with a nurse crop it is strongly recommended that the grain be seeded at not more than two-thirds the usual rate. This will give the sweet clover a much better chance than when a full seeding is made. When severe droughts occur it may be necessary to cut the grain for hay if the stand is to be saved.

CHOICE OF SEED.

On account of the low germination of much of the sweet-clover seed offered for sale it is very important that seed be tested for germination before planting. Low germination usually is due to the fact that many of the seeds remain hard after they have been in the germinator or soil for a month or more. The seed coats of hard sweet-clover seeds become permeable to water very slowly, if at all, in storage. The germination of such seeds is greatly increased, however, when they are subjected for a time to alternating temperatures, such as freezing and thawing. It is on this account that unhulled seed, which germinates poorly in the laboratory, often will produce good stands when sown during the winter. When sweet clover is to be sown in the spring it is very important that only hulled seed which germinates 75 per cent or more be sown. As explained later under the heading "Seeding," unhulled seed which has a low germination should be used for seeding only during the winter months, so that there will be sufficient time for the alternating temperatures of winter and early spring to cause it to germinate during favorable weather.

Hulled seed usually germinates much better than unhulled seed, as is shown in Table I.

Table I.--_Germination and hard seed content of samples of sweet-clover seed, hulled, and unhulled, from different sources._

Average percentage of-- Number of Description. samples. Germination. Hard Seed. --------------- ---------- ------------ ---------- Kind of seed: Hulled 237 53.25 18.7 Unhulled 45 11.8 70.9

Source of seed: Southern 22 14 60 Northern 22 37 43 Imported 28 56 12

Table I shows that northern-grown seed germinates better than northern-grown seed and imported seed better than either. The low germination of the southern-grown seed is probably due to the fact that a very large percentage of it is flailed out and sown in the hull. Northern-grown seed generally is thrashed with either a grain separator or a clover huller. Imported seed always is hulled. In hulling seed the rasps or concaves of the machines scratch the seed coats sufficiently to permit water to penetrate them, so that the germination is greatly increased. Apparently there is no reason why southern-grown seed when it is properly hulled should not germinate as well as northern-grown seed.

Since the Ames scarifying machine (fig. 8)[7] has been placed on the market, it is possible to buy scarified seed. This machine is so constructed that the seed is forced through a conveyor, part of which is covered with sandpaper. When the seed comes in contact with the sandpaper it is scratched, so that water will penetrate the seed coats. When this machine is run properly the germination of seed is greatly increased, but when carelessly operated germination may be lessened, as many of the seeds may be broken.

[7] This machine was invented by Prof. H. D. Hughes, of the Iowa State College at Ames. A United States patent covering this device has been issued and dedicated to the free use of the public.

The retarded germination of sweet-clover seed may be overcome by soaking it in commercial concentrated sulphuric acid for 20 minutes. It should then be washed quickly, using running water if possible, as sulphuric acid becomes very hot when mixed with small proportions of water. A great deal of water therefore is necessary in order to lessen the danger of burning. The seed should be dried quickly by spreading it out on a floor or canvas, and it should be stirred at intervals. Unhulled seed should never be treated with sulphuric acid. When only a small quantity of sulphuric acid comes in contact with the hulls a very high temperature will result and the seed will be killed. The treatment of seed with sulphuric acid for seeding on a field scale is not to be recommended, in view of the fact that as good or better results may be obtained by using scarified seed.

It is very important that seed of the desired species be obtained. Many lots of sweet-clover seed offered for sale on the market consist of mixtures of the yellow and white species, and many samples also are adulterated with alfalfa. Seed which is simply labeled sweet clover should never be purchased, as seed so labeled may be any one of the several varieties offered for sale. It is always best to state the specific kind of seed ordered and then submit a sample to either your State Agricultural experiment Station or one of the seed laboratories of the United States Department of Agriculture[8] for identification before purchasing.

[8] Samples of seed may be submitted for analysis or identification to the Seed Laboratory of the United States Department of Agriculture at Washington, D. C., or to any of the following laboratories maintained through the cooperation of the Department: Branch Seed-Testing Laboratory, Agricultural Experiment Station, Columbia, Mo.; Branch Seed-Testing Laboratory, Agricultural Experiment Station, Baton Rouge, la.; Branch Seed-Testing Laboratory, Oregon Agricultural College, Corvallis, Oreg.; Branch Seed-Testing Laboratory, Purdue University, La Fayette, Ind.; Branch Seed-Testing Laboratory, California Agricultural Station, Berkeley, Cal.

The Seed Laboratory of the United States Department of Agriculture during the winter of 1915-16 obtained 172 trade samples of sweet-clover seed and, as may be seen from Table II, many of the samples were not true to name.

Table II.--_Trade samples received in response to requests for white sweet clover seed._

Key to Columns [A] White sweet clover. [B] Biennial yellow sweet clover. [C] White and biennial yellow sweet clover. [D] Annual yellow sweet clover.

Number of Seed when tested Seed labeled-- samples. found to be-- Alfalfa and-- [A] [B] [C] [D] [A] [B] [C] White flowering sweet clover, white sweet clover, or Holhara clover, or _Melilotus alba_. 147 91 10 28 -- 13 1 4 Sweet clover 22 6 4 2 5 5 -- -- Not labeled 3 1 -- -- 2 -- -- -- ---- ---- ---- ---- ---- ---- ---- ---- Total 172 98 14 30 7 18 1 4

PREPARATION OF THE SEED BED.

Sweet clover requires a well-settled and firm seed bed, with just sufficient loose soil on the surface to permit the seed to be well covered. When the seed is sown in the spring on winter grain the seed bed usually is in good condition. At this season of the year the seed may be sown, so that it will be covered by freezing and thawing weather. It may be sown also when the ground is in condition to cultivate and then may be harrowed or drilled in. When the seed is sown with spring grain the seed bed is not as firm as it should be for the prompt germination and establishment of the young clover plants. If sown in this manner the soil should be worked into a fine condition and firmed as much as possible. It is good practice to roll the ground with a corrugated roller after seeding. Better stands are usually obtained by seeding on fields that have been disked and harrowed than on those that have been plowed.

When sweet clover is seeded without a nurse crop it should not be sown on freshly plowed land which has had no opportunity to settle. The land preferably should be plowed several months before the seed is to be sown, and then worked at intervals with soil packers or harrows. Double disking and harrowing just previous to seeding are to be strongly recommended in preference to plowing at this time.

When sweet clover is to be seeded in the fall on grain stubble, the ground should be disked and worked into good condition as soon as the grain can be removed. If the seed is sown immediately the field should be rolled after seeding.

Fall-plowed ground ordinarily makes an ideal seed bed for spring seeding. Soil which has been previously planted to a cultivated crop, such as corn, is usually put in sufficiently good condition for sweet clover by disking. Good success has been attained by merely broadcasting the seed on sandy soil and scratching it in with a harrow. Such a seed bed appears to be ideal when the seed can be covered sufficiently to insure plenty of moisture. It must be remembered that young sweet-clover plants are not drought resistant and that every precaution should be taken in seasons of drought or on laud which drought affects badly to so prepare the seed bed that the largest quantity of moisture will be conserved.

Excellent stands have been obtained at times by double-disking native prairie sod and either covering the seed with a harrow or sowing it with a drill.

SEEDING.