56 PREPARING TO PLANT AND PLANTING 



The fertilizers used for the production of potatoes are 

 dry barnyard manure, green manures, and commercial fer- 

 tilizers. I have tested out several commercial fertilizers 

 but without good results. However, the best fertilizers, 

 those containing about 3 or 4% of nitrogen, 6 to 8% of 

 phosphoric acid, and 8 or 10% of potash, give good results 

 one thousand pounds or more being used if spread broad- 

 cast, but if drilled along the rows, less than that amount is 

 used. It should be mixed with the soil to prevent it coming 

 in contact with the seed. The best fertilizers for the pro- 

 duction of good potatoes is barnyard manure, followed by a 

 green crop. This should be spread broadcast over the field. 

 It should be put out in the fall and plowed under just before 

 the sowing of a green crop. The best green manure or mulch 

 is Texas red oats and vetch combined. This makes a heavy 

 crop to turn under before or while plowing for the spring 

 crop. It is a wise policy to combine the green with the dry 

 manure, as the dry fertilizer used alone breeds scab par- 

 ticularly if in close contact with the tubers. 



This is a fact not known to most potato growers. The 

 green crop during its decomposition forms an acid, counter- 

 acting the effects of the dry manure. 



Nitrogen, phosphoric acid, and potash are the three es- 

 sential plant foods in all soils, and are the most liable to be 

 deficient after several croppings. These are the three plant 

 foods needed in fertilizers. The dry manure contains a 

 good per cent of these, and with the combination of this fer- 

 tilizer and the green crop, practically all the plant foods are 

 obtained. Clover is a good cover crop, as it takes the ni- 

 trogen from the air and thence to the soil. It contains more 

 nitrogen than other legumes. 



The "pumps" on the feed roots cannot absorb any plant 

 food unless it is in liquid form. This is the reason that the 



