The most serious objection to seeding sweet clover in the spring without a nurse crop is weeds. In many sections of the country seeds will take as much water from the soil and make as much or more shade than a crop of grain. In spite of the fact that sweet clover will withstand more adverse conditions than red clover or alfalfa, a heavy growth of weeds will greatly retard the growth of the plants and in some cases kill most of them. ([Fig. 10.]) On plats sown in April without a nurse crop at Arlington, Va., it was necessary to mow weeds five times during the summer of 1915 in order to keep them partly checked. Where it is necessary to mow a field so many times the plants are not only checked or killed, but as much time is required for this work as would be necessary to harvest a crop of grain. This trouble may be overcome in part by pasturing the sweet clover the first season, but even then during wet weather it may be necessary to cut the weeds at least once before the plants become well enough established to turn live stock on the field. The plants should at no time be clipped closer than 5 inches from the ground.
After a field of sweet clover has become well established, it may be pastured throughout the summer and fall. Close grazing should be avoided during the summer, or the plants may be killed, but they may be pastured fairly close to the ground in the autumn, as it does not appear as necessary to provide a winter covering as is the case with red clover. Close pasturing or clipping late in the fall has had a marked effect on the growth of the plants the following spring on some fields and no apparent effect on the stand and growth of the plants on other fields. A portion of a field in Livingston County, Ill., was clipped close to the ground in the late fall of 1915. On June 1, 1916, the stand was somewhat heavier on the unclipped part of the field. More noticeable than the thickness of the stand was the fact that the plants on the unclipped portion were 8 to 10 inches higher than those on the clipped area. It is reasonable to believe that plants going into the winter with no protection are more likely to be injured than those having some protection.
On the other hand, many fields in different parts of the country have been closely clipped or pastured in the late fall with no noticeable injury. Because of the value of the hay or pasturage in the late summer and autumn of the year of seeding, it is strongly recommended that the first year's growth be utilized. If the field be cut for hay it is well to leave a 4-inch or 5-inch stubble, as this will serve to catch drifting snow during the winter, thereby adding to the protection against winterkilling. If the field is not pastured the first season and weeds are not troublesome, a cutting of hay may be made when growth ceases in the fall.
Fig. 10.—White sweet-clover plant (at the left), showing the effect of a heavy growth of weeds. Had the weeds not been present the plant at the left should have been larger than the one at the right, as the seed was sown two weeks earlier and the other conditions for growth were ideal. Four-fifths of the plants on the plat which had a heavy growth of weeds were entirely killed.
When sweet clover is seeded with grain, moisture conditions should serve to determine whether the grain should be permitted to ripen or be cut for hay. When untimely droughts appear the plants may be killed if the grain is not cut as early as possible.
In the South and in some sections of the Eastern and North-Central States where the soil contains an abundance of limestone and is well inoculated, a cutting of hay may usually be obtained after a grain crop has been harvested. In other sections of the North in only exceptionally favorable weather will more than pasturage be obtained after the grain is cut.
One of the special advantages of sweet clover is that it produces good pasturage somewhat earlier in the spring than most forage crops. In the North, with the exception of the extreme northern portion of the United States, it will furnish a cutting of hay in June or excellent pasturage until that time and a crop of hay or seed in late summer. In the South two cuttings of hay and a seed crop may be harvested. After maturing seed the plants die. It is a common practice in many sections to pasture the crop until about June 10, when the stock is removed and the plants are permitted to mature seed. If the plants have not been grazed closely they should be clipped at this time, so that the seed crop will ripen more evenly. Sweet clover may be pastured during the entire second season's growth, provided sufficient stock is kept on the field to prevent the growth from becoming woody. If the plants become coarse the pasture may be clipped, leaving an 8-inch stubble, so as to induce a new growth which will be more palatable. If it is desired to have the pasture reseed itself stock should be removed at least eight weeks before heavy frosts are expected, or only sufficient stock should be permitted to remain on the pasture to keep some of the plants in check.