Part 5

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) 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.

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 for identification before purchasing.

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 White sweet clover. Biennial yellow sweet clover. White and biennial yellow sweet clover. Annual yellow sweet clover.

Number of Seed when tested Seed labeled-- samples. found to be-- Alfalfa and-- 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.

The proper time to seed sweet clover should be determined by the germination of the seed, the climatic conditions of the region, and the condition of the seed bed at the time of sowing. When growing under natural conditions, seed which has lain in the ground over winter germinates in sufficient quantity during the following spring to produce a stand. It is therefore assumed that since this seed has passed the winter on or in the ground and has produced a good stand the following spring, sweet clover may be sown at any time of the year and a satisfactory stand obtained. Little is thought of the enormous number of seeds which shatter from a single plant and fall on an area not exceeding 5 or 6 feet in diameter. Single plants have produced as many as 350,000 seeds (the approximate number in 1½ pounds), or about 10,000 seeds for each square foot of ground covered. It matters little how many of these seeds germinate in the fall they mature or during the following winter, when the seedlings will be killed by freezing, for there will be enough viable seeds left in the ground to germinate when conditions are favorable in the spring. Conditions are very different when sweet clover is sown on cultivated soil at the rate of 5 to 20 pounds of seed to the acre--25 to 100 seeds to the square foot. When this quantity is sown, it is necessary that it be planted at such a time that the greatest number of seeds will germinate and produce plants.

HULLED SWEET-CLOVER SEED.

Hulled seed makes up a large percentage of the sweet-clover seed sown. The germination of hulled seed varies considerably, although ordinarily it is higher than that of unhulled seed. Seeding experiments conducted at Arlington, Va., with seed which germinated 80 per cent show clearly that seed which germinates well should not be sown during the winter months in those sections of the country where midwinter thaws are likely to occur, and especially in sections south of the latitude of southern Ohio. In these experiments seed was sown during each month of the winter. Good stands were obtained only on those plats which were sown in the latter part of February and during March and April. At least 75 per cent of the seed sown during November, December, and January germinated on warm days during winter thaws and was killed by later cold weather. Notwithstanding the fact that sweet-clover seedlings will endure fairly low temperatures, seed germinating more than 50 per cent should not be sown during the winter months, and preferably not more than a week previous to the average date for the last severe freeze.

No data have been secured on winter seeding in those portions of the United States where open winters do not occur. It is probable that in those sections the winters are sufficiently cold to prevent germination before spring. Good results may be obtained by winter seeding, but as usually no trouble is experienced in those sections in obtaining a stand by seeding as soon as the soil can be worked in the spring, it is strongly recommended that seeding be done with hulled seed, which germinates well at this time of the year.