No. 6. DEPARTMENT OF AGRICULTURE. 441 



These analyses did not reveal to us the acquired powers of planis 

 to get a minimum of nutrients even when not in an available condi- 

 tion to produce a normal crop. Normally, an acre of wheat needs 

 about 35 tbs. of nitrogen, which it has certain, though iu limited 

 powers of obtaining. An acre of corn needs about seventy pounds of 

 nitrogen, wiiich it has ac(iuired strong power to obtain. An acre of 

 mangels needs 150 lT>s. of polash, while an acre of fix needs only 27 

 tt)s.; an acre of corn needs 20 lbs. of phosphoric acid, while an acre 

 of mangels needs 85 lbs. We see here that different plants require 

 various minimum (juantities of mineral nutrients to produce normal 

 crops, and that they must have the capacity to get these nutrients 

 from sources not in the available state. 



This has been demonstrated by Liebig and many other experi- 

 menters since his day. Liebig raised barley in boxes so constructed 

 that all the water soluble plant food in the soil would be drained 

 off. He analyzed the drain water and determined the soluble plant 

 food it contained, and also weighed and anah'zed the crop of barley 

 and found that 02 per cent, of the potash in the crop was obtained 

 from forms insoluble in water. This experiment shows that barley 

 has strong feeding powers for potash, or that it can get potash from 

 sources not soluble in water. Similar experiments have been made 

 to determine the capacities of our various agricultural plants to ob- 

 tain potash, phosphoric acid, nitrogen, lime, magnesium, etc. 



Plants do not onlj^ have various capacities of rendering plant food 

 soluble, but they have the power of selecting what thej^ need and 

 rejecting what they do not need. Experiments made at the Rhode 

 Island Experiment Station, with plants to which potash and soda, 

 two elements very similar in their chemical properties, were ap- 

 plied; even when the soda which the plant was supposed to use in- 

 stead of the potash, was increased to such an extent that the potash 

 was only in minute quantity in comparison, yet the plant selected 

 and incorporated the potash and rejected the soda. It has been 

 demonstrated through long and tedious experiments that plants 

 have strong feeding powers for some elements of plant food and 

 weak for others; that during certain stages of development the 

 organism will need certain minerals, such as magnesia, in the for- 

 mation of seeds and will then take up more of this element than 

 at any time during the stages of growth, and that they can select 

 what they need and reject what is not necessary. In a general way 

 the feeding powers of the cereal crops are quite similar, with the 

 exception of their capacity of assimilating nitrogen. To obtain the 

 potash and other basic elements for food they seem to have the 

 power to decompose the simpler silicates of the soil, deposit the 

 silica in the leaves and feed on the potash. 



Wheat seems to be the weakest feeding crop among the cereals, 

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