xne iwü ciuei auu general reasous whj' rotation of crops is necessary, according to L. H. Bonham, secretary of the Ohio State Board of Agricultura, are: 1. For the conservation of the Boil. 2. For the sake of economy. Removal of crops takes from the farm nitrogen, phosphoric acid and potash. Reckless farmlog in time depletes the soil below thepointof profitable prodnction, but the soil is practically inexhanstible, since an acre of soil to the depth of one foot contains nitrogen. 8,000 poonds; phosphoric acid, 15,000 ponnds; potash, 12,000 pounds. Commercial f ertilizers are a poor dependence for keeping np fertility. They can only feed the erop in part, and are too costly to be used in storing up fertility for future crops. Fertility is constantly being unlocked by chemical action, by frost and moisture. Nitrification is the most important chemical operation in nature, without which we cannot conceive of continued fertility. The conditions favoring nitrification are: 1. A porous soil. 2. Wannth, as nitrification is dormant at 42 degs. and most active when warm enough to decay meat and vegetable. 3. Moisture in regular and moderate supMy. Clover and grasses shade the soil, ref;ain moisture, render it porous and favor nitrification while rilling in vegetable matter. Nature rotates crops. When the foreste of oak and hickory have been removed a thick growth of evergreens appears. In New England, where white pine forests have been removed, the maple, chestnut and oak have sprung up. A similar rotation is found in timothy meadows, followed by blue grass. Besides a general there is a special depletion by each variety of crops. As each erop seems to have special wants we increase crops by a change, but chemistry has not been able to teil us why. Plants vary in power to appropriate food. Clover, we say, has a high power to gather aitrogen, while wheat has a low power; henee clover precedes wheat well. Wheat grows mostly in cool weather, when nitrification is slow or dormant; henee the soil for wheat must be rich in nitrogen. On the other hand, corn grows wholly in warm weather; henee it needs less nitrogen to make a erop. Plants have f avorites in plant food. Wheat, for example, takes % pounds of potash to every 3% pounds of phosphoric acid. Potatoes take 3 pounds of potash to one pound of phosphoric acid. Plants take food only in soluble or gaseous form. It is a wise arrangement that soil does not dissolve as freely as sugar or salt, or one soaking rain would ruin us. Sturing the soil favors disintegration; henee plowed or hoed crops should f ollow grasses. Grasses are conserves of soil and prevent washing and leaching. Rotation checks some kinds of insect ravages and fungi. The corn root worm does not feed on clover roots. The clover root borer does not bore corn roots or roots of wheat, oats, etc. The smut of wheat does not attack corn, etc. Growing a variety of crops in intelligent or scientific rotation is good economy. It divides the labor of the year, gives regular employment the year round and has many advantages of great significan ce.