Breaking up a well set alfalfa field is no trifling matter. It may be done with three heavy horses, but it is hard work for them, and they will not be able to break more than one acre a day. An authority says the best plan is to use five heavy horses--three in the lead and two on the end of the beam. They can go right along and plow two acres a day. Alfalfa roots are very tough and strong when the plants have attained full growth, and they give a jerky motion to the plow, which is severe on horses’ shoulders. A cast steel plow is the best to use and if it is tempered right a file can just cut it. It can be hammered out thin at the blacksmith’s shop when it becomes too thick to file easily. “The reason for filing, rather than using the hard, thin edge as in other plowing is that the edge needs to be rough as well as thin, or the roots will slip along the sloping edge of the share and not be cut.” It is important that the furrow turned shall not be wider than the plowshare will all the time cut clean, as any main roots that are left uncut will send up a more vigorous growth of stems than before, which, in another cultivated crop will be the same as weeds. [Illustration: Alfalfa Plant and Roots Showing Bacteria Nodules] [Illustration: =Tubercles on Clover Roots= In untreated soil In inoculated soil] _CHAPTER XXI._ Nitro-Culture AN OLD-NEW THEORY The inoculation of soil, like many other lately exploited theories, has no doubt been known for hundreds of years. There are evidences that it was practiced in England at least a century ago, and it is thought to be an old custom among the Chinese. Some space was given to “soil inoculation” in a preceding chapter, attention there being devoted to the simple methods of infecting soil with bacteria. IMPORTANT DISCOVERIES