166 The Potato 



are used for driving and steering, the tool itself taking the 

 place of the other wheels of the tractor. One operator 

 handles both engine and tools. Similar small engine- 

 propelled tools are being made for garden use. 



Engines are being used on potato sprayers to give better 

 results by higher pressures than horses can furnish. The 

 elevating and separating machinery of potato diggers is 

 sometimes driven by engines, horses being used to draw 

 the tool only. 



Harrows or leveling tools are usually used once; occa- 

 sionally twice. Weeders may be used up to a dozen times 

 in extreme cases and half a dozen pay well. Cultivators 

 are used from three to eight times with four or six as 

 the most common number. Outside of Maine, the ridging 

 tools are used once or twice. Thorough tillage and a good 

 condition of the soil before planting necessitate less work 

 later. It is a good rule to cultivate after every heavy 

 rain, and to cultivate more frequently in hard soils than in 

 light. Tillage is less needed in soils which are mellow and 

 full of organic matter, because such soils supply plant-food 

 and water more readily. 



The danger of the growing tubers protruding out of the 

 soil and being sunburned is prevented by ridging lightly 

 after the tubers are formed. Ridging earlier does not pre- 

 vent sunburn because the depth at which the tubers form is 

 controlled by the depth of planting. Very shallow plant- 

 ing results in the tubers forming below the seed and very 

 deep planting in forming at a depth where little sunburn- 

 ing results. Usual depths of planting are not deep enough 

 to entirely prevent sunburn. While late ridging is some- 

 what feasible, the difficulty is that any injury to the roots 

 of the growing potato plant at that stage is dangerous. 



Tillage is so necessary in potato-growing for the libera- 



