224 SOILS AND FERTILIZERS 



303. Roots. Mangels are gross feeders and re- 

 move a larger amount of fertility from the soil than 

 any other farm crop. 74 When fed -to stock and the 

 manure is returned to the soil they materially aid in 

 making the plant food more available for delicate 

 feeding crops. Mangels are better able to obtain their 

 phosphoric acid than are turnips and need the most 

 help in the way of nitrogen. Turnips are surface 

 feeders with stronger power of nitrogen assimilation 

 than the grains, but with restricted power of phos- 

 phate assimilation. Manures for turnips should be 

 phosphatic in nature. 



304. Rape is a type of strong feeding plant capa- 

 ble of obtaining its food under conditions adverse to 

 grain crops. When grown too frequently upon the 

 same soil it does not thrive. On account of its great 

 capacity for obtaining food, it is a valuble crop to 

 use for green manuring purposes. 80 



305. Buckwheat is a strong feeding crop and its 

 demands for food are easily met. On rich soil, a rank 

 growth of straw results, with poor seed formation. 

 Buckwheat is usually sown upon the poorest soil of 

 the farm. Being a strong feeder it is used as a 

 manurial crop, being plowed under while green to 

 serve as food for weaker feeding crops. 



306. Cotton. On average soils cotton stands in 

 need first of phosphoric acid, second of nitrogen. 81 It 

 is most able to obtain potash. Organic nitrogen as 

 cottonseed meal and stable manure appear equally 

 as effective as nitric nitrogen. Phosphoric acid must 



