EXPERIMENT STATION BULLETINS. 337 



PREPARATION OF THE SOIL 



The potato requires a deep, mellow seed-bed so that its roots can extend 

 easily into the soil and secure moisture and plant food. The depth of plow- 

 ing will be determined largely by the character of the soil. Sandy types of 

 soil are usually plowed to a depth of four or five inches, while heavier types 

 that are well supplied with humus are frequently plowed to a depth of seven 

 inches or more. The soil should be plowed as deeply as possible without 

 turning up much of the subsoil. 



Fall plowing generally gives good results unless the soil is very light and is 

 subject to blowing. Heavier types of soil and those that are covered with 

 sod are usually benefitted by fall plowing. The organic matter that is 

 plowed under in the fall rots and puts the soil in a good condition. 



Spring plowing should be done early so that the soil moisture will be con- 

 served, and so that the organic matter that is plowed under will have time to 

 decay partially before the potatoes are planted. This decaying organic 

 matter will aid materially in holding the soil moisture. If the sod is cut up 

 with a disc harrow before it is plowed in the spring, it will rot more quickly 

 and will make a better seed bed. 



Both fall plowed and spring plowed lands should be harrowed thoroughly 

 as soon as possible in the spring, so that the soil will be put in a mellow con- 

 dition and so that soil moisture will be conserved. The disc harrow is a very 

 effective implement for cutting up sods and working them down in the soil^ 

 On fields that are stony, however, the spring-tooth harrow is more generally 

 used. After the soil has been pulverized to the depth of the furrow slice by 

 the disc or spring-tooth harrow, it should be gone over several times before 

 planting time with a spike-tooth harrow or drag to smooth the surface and to 

 kill weed and grass seedlings. Thorough tillage at this time will save much 

 labor later in the season in controlling weeds and grass. 



THE USE OF MANURE 



Stable manure should be used in the rotation since it adds plant food in 

 the form of nitrogen, phosphoric acid, and potash, improves the physical 

 condition of the soil, and promotes the growth of beneficial soil bacteria. 

 As far as possible, dairy farming or some other branches of animal industry 

 should be carried on in connection with potato growing, so that manure will 

 be available for the land. 



Fresh stable manure applied late in the spring may promote the development 

 of potato scab. This disease is caused by an organism that lives in some 

 soils, as well as on the seed potatoes. The scab organism thrives best in 

 alkaline or sweet soils. The ammonia in fresh manure is alkaline and tends 

 to sweeten the soil, thus encouraging the growth of the scab organism. 



In dry seasons, coarse, strawy manure when applied late in the spring 

 may make the soil too porous and cause it to dry out quickly. It is a good 

 practice to apply stable manure to the haj^ crop that precedes the potatoes in 

 the rotation. The application should be made during the summer previous 

 to potato planting. The growth of the hay crop is increased and there are 

 more roots and stubble to turn under for humus. The manure rots thor- 

 oughly by the time the potatoes are planted, and much of its plant food is 

 available for the potato crop. If applied directly to the potato crop, it is 

 generally best to put it ou during the fall or winter as a top dressing. The 



