Climate, Soils and Rotation 93 



common observation that a small amount of rainfall at 

 this time may be worth much more than larger amounts 

 at other times. As this comes immediately after the 

 critical period in the life of the potato, it will be seen that 

 every effort should be made to keep the plant well sup- 

 plied with water by tillage, organic matter, and the like. 



Soil texture 



The root system of the potato is weak and small com- 

 pared with that of other standard farm crops, such as 

 corn. It is especially weak in penetrating heavy soils. 

 In any soil, loose texture greatly favors the potato by allow- 

 ing wider and deeper distribution of the roots. The de- 

 velopment of the tubers is checked and rendered irregular 

 unless the soil is loose and open in texture. Most of the 

 early crop for sale in summer is grown on sandy soils. 

 On account of their advantages in structure, potatoes would 

 be raised only on sandy soils did they not have other dis- 

 advantages which offset the value of good structure and 

 earliness. Too great soil heat and lack of moisture often 

 limit the yield of potatoes grown on sandy soils as a late 

 main crop in summer. Much of the w^ork of the potato- 

 grower must be directed to give heavier soil types a struc- 

 ture more loose and open. Increasing the proportion of 

 organic matter loosens up the structure of soils. Some of 

 the greatest potato-growing soils naturally possess plenty 

 of organic matter, as the Aroostook soils and the tule 

 lands of California. The increased value of irrigated 

 soils for the potato-growing where organic matter is sup- 

 plied by rotation with alfalfa, or the use of humus-produc- 

 ing cover crops in the South, shows the importance of or- 

 ganic matter. There are few American soils which are not 



