Feb. II, 1918 Water Extractions of Soils and Crop Production 



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incident to the production of a good crop. If the soil is not capable of 

 sustaining such losses, it is extremely probable that crops will suffer from 

 a lack of nitrates. 



Table V. — Water-extractable matters with reference to seasonal withdrawals of a good crop 

 [Expressed as parts per million of soil] 



When we turn to the poor soils, we see that they all had in the un- 

 cropped condition more than enough nitrate to supply the actual amounts 

 withdrawn by a good crop; but all were incapable of sustaining addi- 

 tional losses of the magnitudes, which we must regard as normal. 



Phosphate. — The figures for all soils under crop plus the requirements 

 of a good crop are invariably greater than the amounts in the uncropped 

 soils. If the figures for these latter represent in each case the maximum 

 amount of soluble phosphate the soil is able to hold in that condition, 

 it is quite clear that either the plant absorbs insoluble phosphate, or the 

 good soils replace the soluble phosphate as rapidly as it is required by 

 the plant. The latter explanation appears the more probable. But the 

 computed deficiencies of the poor soils are no greater than those of the 

 good soils, nor are the soluble phosphate contents of the former less than 

 many of the latter. The rate of solution of phosphate in the good soils 

 must be very high and we can find no reason to conclude that the poor 

 soils are in any way inferior in this respect. 



Basic ions. — The amounts of basic ions in cropped soils plus the 

 requirements of a good crop are usually less than the amounts in the 

 uncropped soils. We note two exceptions to this in the poor soils Nos. 



