296 Journal of Agricultural Research voi. xvi. no. h 



well for another year, when a mistake was made in watering by the farmer, 

 the ground became water-logged, and the entire field was lost through 

 blight in the mature stage. 



SOIL CONDITIONS AND IRRIGATION 



Soil conditions materially assist the plant or the fungus. If the 

 ground is well moistened and loose when the seed is planted, a strong 

 vigorous start may be obtained by the plant which will carry it well 

 beyond the immediate reach of the fungus. It has been the common 

 practice to withhold irrigation until the new tubers begin to set. If the 

 plant can endure withholding artificial watering until the new tubers 

 set, it is well to delay, but to postpone it until the plant is suffering 

 acutely, brings it to a condition from which it never wholly recovers. 

 The fungus will make headway in a drouthy plant. After irrigation 

 water has been supplied, it is expedient to cultivate deeply, because 

 irrigation water packs the soil tightly. Too great an application of 

 water on heavy soil may leave the soil puddled, in which condition it 

 must remain for several days before cultivation is possible. If this is 

 accompanied by a rising soil temperature, the ill effects are increased. 

 Occasionally a heavy rain will puddle the soil late in the season preced- 

 ing harvest. This may occur on ground irrigated too late. In such an 

 event it is common for the plants to blight generally and die. The 

 damage now is not in the death of the foliage or the death of the plant, 

 but in the rot which will attack the new tubers. This is a black-rot 

 which may enter by way of the stolons, a common method, or through 

 wound or lenticel. When such tubers have begun to rot, they are a total 

 loss. If the rot has not been detected in the field, it may occur later 

 in the bin, causing a worse trouble. All the tubers of a plant may not 

 be attacked, however, and in such a case control consists in getting them 

 out of the ground without delay. Early varieties in which the new 

 tubers have time to come to full ripeness are more susceptible than late 

 varieties. 



At this time correct irrigation practice is unknown. No rule can be 

 formulated, because each piece of ground requires different treatment. 

 During some years it is expedient to "irrigate up," meaning to water 

 the field immediately after planting. If the soil is too dry, irrigation is 

 necessary for germination and will carry the plant for the maximum 

 length of time before rewatering. Harm results if the water applied in 

 addition to the soil moisture present creates an excess. Irrigation of a 

 plowed field in which nothing has been planted is impractical, owing to 

 the absence of row ditches, and the fact that a certain time must elapse 

 before anything can be planted. Cultivation should be given after each 

 irrigation, so long as it can be done without damaging the plants below 

 ground. Sandy soils need less cultivation than heavy soils. The best 



