FOR BETTER CROPS IN THE SOUTH 



23 



that the actual percentage composition in mineral plant food 

 does not fully measure the possible productive capacity of sandy 

 soils as compared with more compact silt or clay soils. 



As a general rule if the three elements, nitrogen, phosphorus, 

 and potassium, be added separately to three different plots 

 of very sandy land, the nitrogen will increase the yield, while 

 little or no increase will be produced by either phosphorus or 

 potassium. After plenty of nitrogen has been provided, then 

 the addition of potassium will still further increase the yield. 

 Actual results obtained on the University of Illinois soil experi- 

 ment field on the sandy land, will serve to illustrate this: 



Crop Yields in Soil Experiments 

 Sandy Soil near Green Valley, Illinois 



Soil Treatment Applied 



1909 

 Corn 

 Bu. 



Nitrogen 



Phosphorus 



Potassium 



Nitrogen, phosphorus 

 Nitrogen, potassium 



13 

 13 

 65 

 74 



It will be noted that where nitrogen was applied, the yield is 

 more than double that obtained with either of the other elements. 

 Except in 1902, phosphorus shows some effect when added to 

 nitrogen, but potassium with nitrogen is more effective, especially 

 in 1905, when it gave a yield of wheat thirteen bushels higher 

 than was obtained with nitrogen alone. It should be stated, 

 perhaps, that it is exceedingly difficult to select a number of 

 exactly uniform plots for experimental use on this kind of soil 

 and small differences may be attributed to soil variation, but the 

 marked and uniform effects of nitrogen, and of nitrogen with 

 potassium, are characteristic of such soil, and the further addi- 

 tion of phosphorus may sometimes prove profitable. 



These results help to explain the marked effect of farm manure 

 on sandy soils, especially when used for a crop rotation which 

 includes legumes. Both the legumes and manure will furnish 

 nitrogen, and the manure is also well supplied with potassium, 

 the bedding being rich in potassium, and all potassium in the 

 feed being returned in the manure. It may be noted that on 

 very sandy lands clover does not grow well, but either cowpeas 

 or soy beans is an excellent substitute for clover, as both do well 

 on very sandy soil. 



It is exceedingly important that so far as possible all crops 

 shall be fed and the manure shall be carefully saved and re- 

 turned to such land, not only for its plant food value, but also 

 for the organic matter which is needed to improve the physical 

 condition of the soil, 



