Importance of Nitrogen to Growth of Plants. 



247 



water equal to twice the weight of soil for three minutes and allowing it 

 to stand and pouring off, this being the conventional method, now em- 

 ployed for determining the water-soluble salts. If this extraction is a 

 measure of the plant-food, then there was no plant-food in the soil after 

 this operation. 



The soils thus treated and soils not extracted were then allowed to 

 stand for a month in open jars without the addition of water, so tltat 

 they became in appearance very dry before the end of the period. Cab- 

 bages were then raised by the basket method in this leached soil and 

 also in the soil which had not been leached as shown in figure 85 with 

 the following results: 



Table XV. Showing Green Weight in Grams of Cabbages on Poor 

 AND Good Cabbage Spots Leached and Unleached. 



Good. 

 Poor. 



Leached. 



Table XVI. Showing the NO3 in Parts per Million in Original Soil not 

 Planted, and Soil from same Source after Crop had been Grown, 

 Samples for Analysis being taken two months after Original Soil 

 was Leached but Immediately after Crops were Removed in case of 

 Soil Growing Cabbages. 



Apparently not the only factor in the growth of crops is the amount 

 of water-soluble nitrogen, since leaching improved the growth of cab- 

 bage, both on the good and poor spots ; but whatever this untoward 

 influence may have been, which the leaching appeared to eliminate, it 

 was very small compared with the apparent influence of water-soluble 



nitrogen. 



This experiment brings out two possibilities of the highest signifi- 

 cance. It appears from this experiment that a soil leached of its water- 



