ROTATION OF CROPS, the order in which crops are grown during a series of years on the same land. The advantages of this prac tice are: (1) All plants tend to exhaust the soil, but in different degrees, hence a rotation tends to maintain a balance. Thus at the Rotharnsted Experiment Station, England, where wheat has been grown on the same land for 62 successive years without manure or fer tilizers, the average yield is about 13 bushels per acre, or nearly the same as the average yield in the United States, while where grown in a four course rotation of rutabagas, barley, beans or clover, wheat, the average yield during a period of 52 years is nearly 27 bushels per acre, with out manuring or fertilizing. (2) All plants do not take up the same ingredients in the same proportion; thus, crops rich in carbonaceous matter take up relatively small amounts of food from the but large quantities from the air, the latter costing nothing. (3) Some crops give better opportunity for cleaning land, as corn, potatoes. Others cannot be tilled and favor the growth of weeds, as wheat, oats. (4) When several crops are grown on a farm the labor is distributed over a greater portion of the year and it is more economical. The social evils consequent on temporary employment at highs wages for a short period of the year, and idleness the rest of the time, cannot be over looked. (5) Plants vary in their ability to assimilate the plant food in the soil; thus buck wheat and rye are able to flourish where wheat and cabbages could hardly live. (6) The legumes enrich the soil in nitrogen. (7) A variety of crops is essential where cattle and other livestock are kept. (8) In a rotation the increase of destructive insects and diseases is hindered, owing to their not having the neces sary crop to prey upon. (9) Some crops per mit the sowing of others among them, thus saving time; clover and grass seeds being sown among barley and wheat, wheat sown among corn. (10) Some crops permit the aggrega tion of the soil particles when they become ex cessively reduced by tillage, hence land is laid down to grass, alfalfa. (11) Certain crops aid in accumulating humus, as grass, hence such should follow two or three years of exhaustion by .tillage. Admitting air to the soil tends to destroy humus and to reduce the water-holding capacity. The loss of humus has converted garden-spots in New York and other Eastern States, northern Africa, Asia Minor and Spain into wastes, and Sicily, the granary of Italy in the time of the Romans, is now comparatively sterile.
Rotations are described according to the number of years required to complete a circuit, as three-course, four-course, etc. In the latter the tillable land .is divided into four parts and each crop is grown on part of the farm each year. The folly of growing the same crop on the same land for several successive years was noted by the Romans and others, as also the benefits derived from growing a leguminous crop, as alfalfa or clover, previous to a grain crop, as wheat. These observations remained unutilized until a comparatively recent date. Rotations have gradually grown into their present forms according to circumstances, and have been and are modified as required and as our knowledge increases. Attention was first drawn to their value in 1777, in a treatise by Dickson of Edinburgh, Scotland.
One of the earliest recorded systems was the "outfield" and "infield," in which part of the land was used for growing grain until its crop producing power was so reduced that it became unprofitable, when it was allowed to lie idle for a number of years. Increase of population caused a modification, the land being rested or "Lamed" a year at intervals; thus, among the Jews, this was repeated every seventh year. A system of continuous single cropping has been pursued in the Western States with distinct loss to the nation. Where land is weedy and in dry districts, as parts of California, the east of England, etc., bare fallowing or the cultivation of the soil without growing a crop is still con sidered good practice, sufficient moisture being conserved to ensure a profitable crop the suc ceeding year. A development from this system consisted of the introduction of green crops, either intertillage crops, as corn, turnips, pota toes, cabbages, etc., if the land was weedy and needed cleaning, or of legumes, as clover. The advantages of a crop-fallow are that the land is turned to profitable use; it ;s cleaned and the available nitrogen present as nitrates is not so liable to be lost by percolation, being taken up by the crops; that humus is produced from the root-residue; and that if a leguminous crop is grown it enriches the soil in nitrogen by means of the bacteria on its roots.