EXPERIMENT STATION BULLETINS. 233 



the equivalents of what is removed by the crop. Such a soil requires a 

 fertilizer whose constituents are all available, that is, read}' for immedi- 

 ate use. Such a fertilizer would have its nitrogen in the form o.f nitrate 

 of soda,' or sulphate of ammonia, its phosphoric acid would be in the form 

 of dissolved rock or dissolved bone, and its potash would be in the form 

 of sulphate, muriate or carbonate. In this case, to supply the immediate 

 needs of the growing crops should be the direct object of the use of fer- 

 tilizers. In a soil heloic the normal in fertilizing constituents not only 

 should the fertilizing requirements of the crop receive attention, hut the 

 soil should he fed us iccll. The huildiug of the soil is accomplished by the 

 application of fertilizers less readily available. Such fertilizers would 

 have their nitrogen in the form of blood, tankage, cotton seed meal, bone 

 meal, or digested leather. Their phosphoric acid would be in the form of 

 raw bone meal, steamed bone meal or South Carolina rock. The availa- 

 bility of potash need not be a matter of concern for in most fertilizers it 

 is equally available. 



HUMUS. 



All productive soils contain a considerable amount of organic matter, 

 usually termed humus. An abundance of humus portrays a healthy con- 

 dition of the soil, as far as the nitrogen supply is concerned. The supply 

 of humus is kept up in two ways : first, by rotation with leguminous crops 

 and green manuring. Second, by the liberal application of barnyard 

 manure. Farmers do not yet sufiiciently realize the extent to which they 

 impoverish their land by a failure to return in barnyard manure the 

 organic equivalent of what is removed by the crop. Commercial fer- 

 tilizers will be used in vain, if the humic condition of the soil is not con- 

 stantly replenished. To hotter secure this end it is well to consider com- 

 mercial fertilizers as supplementary to the barnyard manure and in most 

 instances they should be used in connection therewith. 



THE ESSENTIAL PLANT REQUIREMENTS. 



There have been proven to be thirteen elements more or less essential to 

 plant growth. Of these, however, the agriculturists need be concerned 

 for but three, namely, nitrogen, phosphoric acid and potash. All of 

 the others are present in nearly all soils to a sufficient extent to satisfy 

 the needs of vegetation. Just why and in what way these three ingredi- 

 ents are so essential is not known. What is known is that vegetation 

 cannot exist in the absence of any one of the three. This suffices to ex- 

 plain the need of fertilizers. We are not as yet able to feed the plant, 

 so to speak, we can but furnish the raw materials and the plant must do 

 its own arranging and assimilating. Inasmuch as plants will not grow 

 in the absence of available nitrogen, phosphoric acid and potash we 

 know that these materials are essential. We then in commercial fer- 

 tilizers furnish these three materials to the plant. It does its own arrang- 

 ing and building into such complex nitrogenous substances as "gluten." 



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