338 iSTATE BOARD OF AGRICULTURE 



usual rate of application is eight or ten loads to the acre. Manure should 

 be uniformly distributed. It should not be placed in the row where it will 

 come in contact with the seed jjieces or the growing tubers, since such prac- 

 tice may cause the development of potato scab. 



THE USE OF LIME 



The potato crop is quite tolerant of acid soil. In order to get satisfactory 

 yields of potatoes it is necessary, however, that such crops as alfalfa, sweet 

 clover and clover be grown in the rotation to supply plant food and humus. 

 These plants require soils that are sweet, or rich in lime. Most of the potato 

 soils of Michigan need lime in order to grow alfalfa and clover. 



Lime applied shortly before the potatoes are planted may promote the 

 development of potato scab, since it acts the same in this respect as does 

 fresh stable manure. Lime, therefore, should generally be applied just 

 previous to the sowing of alfalfa or clover, or at the time of preparing the 

 seed beds for these crops. The usual rate of application recommended is 

 two tons of ground limestone, or six loads or more of marl, or one and one-half 

 tons of hydrated lime per acre. 



COM^MERCIAL B^ERTILIZERS 



The potato crop should not lack for available plant food at any time 

 during the growing season if maximum yields are to be obtained. The plant 

 food elements in commercial fertilizers are generally more quickly available 

 to the growing plant than are those in barnyard manure or clover or alfalfa 

 sod. For this reason commercial fertilizers can generally be used to advan- 

 tage to supplement the stable manure and sod. 



The kind of fertilizers and the amounts to use is determined largely by 

 soil and climatic conditions. Potatoes grown on sandy types of soil that are 

 lacking in organic matter generally respond to a complete fertilizer that 

 analyzes approximately 4 per cent nitrogen, 10 to 12 per cent phosphoric 

 acid, and 3 to 6 per cent potash, applied at the rate of 400 to 800 pounds 

 to the acre. Loamy types of soils that are well supplied with organic matter 

 generally give increased yields of potatoes when they receive applications of 

 300 to 600 pounds of 16 per cent acid phosphate to the acre. 



Of the three elements, nitrogen, phosphoric acid and potash, the phosphoric 

 acid is the one that generally gives the most consistent results when applied 

 in the form of commercial fertilizer. Most of our potato soils are deficient in 

 phosphoric acid. Furthermore, stable manure and alfalfa or clover sod that 

 is turned under contain only one-half to one-third as much phosphoric acid 

 as they do nitrogen and potash. 



Commercial fertilizers will give better results in seasons of sufficient rain- 

 fall. In very dry seasons the lack of moisture limits the development of the 

 plants and makes them less able to utilize the plant food applied. There- 

 fore, in sections subject to long periods of drought heavy applications of fer- 

 tilizer are not so generally warranted as they are in regions where droughts 

 are less frequent and soils are more retentive of moisture. One way of 

 making commercial fertilizers more effective is to improve soil moisture 

 conditions by plowing under organic matter. 



Fertilizers should be placed in moist soil so that they will dissolve. They 



