210 



It is almost universally conceded that clover should be included 

 in every system of rotation. Experiments tend to show that one ton 

 of clover is equal to four tons of barn-yard manure. The choice of 

 rotating crops must, however, depend largely upon the soil, climatic 

 conditions, and the knowledge possessed by the farmer. It is, and 

 should be, the aim of the farmer to crop his land so as to get the 

 largest cash return, and he should adapt any system to that end. 

 (Ohio Ex. Sta. B. 96; Univ. of Minn. B. 190; Univ. of Tenn. B. 90; 

 S. Dak. Ag. Col. B. 98; Bu. Pit. Ind. B. 187; Miss. Ex. Sta. B. 101; 

 R. I. Ex. Sta. B. 74, 75, 76, 135; Univ. of 111. B. 141.) 



Notes. In some instances, as in the case of grain farms, it has 

 been necessary to increase the proportion of the farm sown to grass. 

 The continuous cropping of grain practiced so many years has re- 

 duced the amount of vegetable matter in the soil and increased the 

 amount of weeds until the crop yields are so low as to make grain 

 growing unprofitable. On such farms it is undoubtedly profitable to 

 increase quite largely the proportion of the farm sown to grass, even 

 though there is but little use for the hay, owing to the desirable 

 effect the grass will have in building up and cleaning the soil. There 

 are few cases in which roughage thus grown cannot be put to some 

 profitable use, either by increasing the amount of live stock kept on 

 the farm or at least buying stock cattle or sheep to feed during the 

 fall and winter. 



It should be understood that the growing of clover produces 

 several effects on the land and upon subsequent yields of other crops, 

 only one of which is due to the nitrogen secured from the air. In 

 fact the chief effect of clover in increasing the yield of a subsequent 

 crop of corn is not due to the nitrogen secured from the air, but 

 rather to the liberation of phosphorus by the decay of the clover 

 residues in the soil. The physical improvement of the soil and sub- 

 soil are also important factors in some cases. (Univ. of Minn. B. 

 190; Univ. of 111. B. 125.) 



Another factor, and one that is gaining some prominence at the 

 present time, is a proper sanitary environment for the roots. In- 

 vestigations of the Bureau of Agriculture at Washington arouse the 

 suspicion that the apparent exhaustion of soils is not due so much 

 to the depletion of the stock of plant food as to the lack of proper 

 sanitary conditions. Animals forced to exist in an atmosphere ren- 

 dered foul by their own poisonous exhalations soon cease to thrive; 

 the plant above ground likewise gives up waste products, which if 

 not removed, become a menace to its safety ; is it not therefore natural 

 to expect that from the roots of the plant also there are excreta that, 

 if allowed to accumulate, threaten its very existence? As proper 

 ventilation is necessary to insure the health of the animal, as 

 diffusion, drafts and winds must bring fresh air to the leaves, so 

 must tillage or other treatment purge the soil of the injurious sub- 

 stances cast off by the roots. In this purifying process it is believed 

 that air, and therefore cultivation and drainage, play an important 

 part; certain fertilizer ingredients are effective under certain condi- 

 tions, but more potent still is organic matter in the form of humus. 



