FERTILIZERS FOR GRASS CROPS 225 



be applied in the most available forms. In fertilizing 

 cotton, the use of green manuring crops as cow peas 

 with an application of marl gives beneficial results. 

 Marl, which is composed mainly of calcium carbonate, 

 combines with the acids formed from the decay of 

 this vegetable matter and as a result the plant food of 

 the soil is more available, a result which is beneficial 

 to both soil and crop. There are but few crops which 

 respond so readily to fertilizers as cotton. 



307. Hops, The hop plant is exacting in regard 

 to its food requirements. An excess of easily soluble 

 plant food is injurious while a lack is equally so. An 

 abundance of food in organic forms is most essential. 

 Heavy dressings of farm manures may be applied. 

 Where hops are grown there is a tendency to use all 

 of the manure on the hops while the rest of the farm 

 is left untnanured. Very light applications of com- 

 mercial fertilizers may be used in connection with 

 stable manure, but such use should be made only 

 after a preliminary trial on a small scale. 



308. Hay and Grass Crops. Most grass crops have 

 shorter roots than grain crops ; they are surface feed- 

 ers and not so able to secure mineral food. When a 

 number of crops have been removed the soil may stand 

 in need of available mineral matter. Farm manures 

 are particularly well adapted for fertilizing grass. Ap- 

 plications of nitrogenous manures result in discourag- 

 ing the growth of clover. Heavy manuring of grass 

 land has a tendency to reduce the number of species 

 and one kind is apt to predominate. 82 On some soils 



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