82 



face of the ground or by being used up by weeds. The end sought in 

 ploughing and cultivation is to control the water supply by removing 

 weeds and leaving the surface of the soil covered with a loose, dry 

 mulch to retard evaporation. Many of our crops require no subsequent 

 cultivation after they are put into the ground. Wheat, oats, rye, clover, 

 grass, forest trees, and, in general, such crops as cover and shade the 

 ground are not, as a rule, cultivated during their period of growth. On 

 the other hand, such crops as corn, tobacco, cotton, potatoes, and fruit 

 trees require cultivation during their early growing period, although 

 even with these crops cultivation ceases after they have attained consi- 

 derable size, and is rarely practiced during the ripening period. 



The principal object of ploughing is to loosen up the soil, for four 

 purposes : (1) To enable the soil to absorb the rainfall more quickly and 

 more freely than it would in its undisturbed condition ; (2) to maintain 

 more of the rainfall near the roots of plants ; (3) to admit fresh air to 

 the roots of plants ; (4) to enable the roots of the young or quickly 

 growing plants to penetrate the soil more easily. 



The principal objects of subsequent cultivation, whether with plough, 

 cultivator, cotton sweep, harrow, hoe, or rake, are (1) to prevent loss of 

 water by weeds and grass, which use up great quantities ; (2) to keep 

 the surface covered with a loose, dry mulch in order to prevent, so far 

 as possible, loss of water by evaporation. Water is thus conserved for 

 the use of crops, and the supply is more abundant and more uniform 

 than it would have been without the cultivation. 



A soil with a compact surface quickly dries out, and the water supply 

 fluctuates rapidly and excessively, to the detriment of most crops 

 during their growing period. Weeds and grass are generally to be ex- 

 cluded from the crop because they transpire great quantities of water 

 which would otherwise have been at the disposal of the crop. Weeds 

 are, however, occasionally of advantage to the crops, especially during the 

 ripening period, because they help to dry out the soil and thus hasten 

 the maturity of the crop 



Some of our crops, therefore, do not require cultivation, because 

 they shade the ground and prevent evaporation and prevent grass 

 and weeds from springing up and diminishing their supply of water, 

 or because they are deeply rooted and can bring water up from con- 

 siderable depths. Other crops can not protect their water supply 

 in this way, and it must be artificially controlled by methods of 

 cultivation. 



PRINCIPLES OF PLOUGHING. 



The common plough is essentially awedge-shaped instrument, which 

 is forced through the soil to loosen it. The topsoil is forced aside 

 thrown up, and usually turned over. This action loosens the soil by 

 separating the soil grains. The loose soil occupies moi*3 space than the 

 compact soil did, and a cubic foot of the former, therefore contains 

 more space for water to enter. Each separate space, however, is also 

 larger and has less capillary action and a smaller power of drawing 

 water to the surface. If the soil, by reason of its fine texture or wet 

 condition, is lumpy after the ploughing, the spaces in the soil will be of 

 very uneven size, and it frequently happens that the surface of the 

 ground is not left in a suitable condition to draw water up from below 



