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Chemical Estimation of the Fertility of Soils in Fulton 

 County, Indiana. 



R. H. Carr and W. K. Gast — Purdue University. 



During recent years there has been an effort on the part of many 

 States to invoice their soils as to plant food content in addition to mak- 

 ing the usual survey in order to classify them into types and series. 

 This invoice is useful first to the farmer in pointing out any deficiencies 

 or excesses in the soil's food supply, and second to the State in estimat- 

 ing the wealth, since this usually resides in the fertility of the soils. 

 Usually only the plant food elements are determined which seem to be 

 the most important or have the greatest influence in modifying crop 

 yield. They are the following: total organic carbon, total nitrogen, 

 total phosphorus, total potassium, total calcium, total inorganic carbon. 

 The test for the last is made for the presence of limestone, the absence 

 of which often indicates soil acidity. There are many factors other 

 than plant food concerned in producing a crop on any piece of land, 

 as rainfall, tillage, drainage, etc., but deficiencies in these can be de- 

 termined often by observation. But a deficiency in the main chemical 

 elements is not so easily estimated and is a matter of life or death to the 

 plant. 



Availability of Plant Food. 



Much discussion has arisen over the availability of these plant foods 

 even when analysis has shown plenty to be present. It is conceded, 

 however, that it is possible to make two per cent of total nitrogen, one 

 per cent of phosphorus and one-fourth of one per cent of potassium 

 available in one year by approved agriculture methods. If this were 

 true, or somewhere near true, it would make a big difference in the 

 crop yield to be expected whether there were 500 or 5,000 lbs. of phos- 

 phorus or nitrogen, etc., present per acre to a depth of six and two- 

 thirds inches. 



Plant Foods Present in a Good Soil. 



It is difficult to set a definite standard of plant food content, but if 

 we choose samples of our productive loam soils frequently producing 



