STUDIES IN PLANT NUTRITION. II.* 



W. H. JORDAN. 

 SUMMARY. 



i. Experiments were conducted in a Station forcing house during 

 the years 1900-1, 1901-2 and 1903-4 with a view to ascertaining 

 what is the essential minimum amount of phosphoric acid and 

 potash which must be available to plants in order that maximum 

 growth may be secured. 



2. In one set of boxes the basal ration supplied all needed elements 

 save phosphoric acid, this being added in progressive quantities to 

 the several boxes. In the other set of boxes, the basal ration supplied 

 all the necessary elements save potash, which was added in progres- 

 sive quantities to the several boxes. 



3. The experimental plants included barley, peas, tomatoes, 

 tobacco, buckwheat, rape, and turnips. 



4. The growth of the plants was, in most instances, such as would 

 be satisfactory with field-grown crops, the production of dry matter 

 with barley being in two of the three experiments beyond what 

 could reasonably be expected in a farm crop. 



5. Up to . a somewhat indefinite point, the production of plant 

 substance increased with the increase in the supply of the variable 

 constituents, but beyond this point the utilization of both phos- 

 phorus and potassium compounds increased without any consistent 

 and well defined corresponding increase of the plant growth. 



6. The data secured do not permit the estabhshment of any 

 definite minimum relation between the intake of phosphorus and 

 potassium and the dry matter produced. 



7. The results secured indicate that what a given crop contains 

 of certain elements is not necessarily to be regarded as a measure 

 of what must be supplied in order to meet the needs for maximum 

 growth. 



THE NECESSARY SUPPLY OF PLANT FOOD. 



INTRODUCTION. 



The question is often asked by farmers concerning the production 

 of a particular crop, " How much nitrogen, phosphoric acid and 

 potash does it (the crop) remove from the soil?" The assumption 

 in this question evidently is that what a plant uses in growth repre- 

 sents its needs, and indicates what should be supplied either from 

 the soil or in a fertilizer. 



Such an assumption can hardly be considered sound. It is well 

 known that some plants, tobacco for instance, grow with equal 



* Reprint of Bulletin No. 360, February, 1913. 



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