160 



Twenty-First BrENKiAi, Bepobt 



lation between availability and solubility. (Se« biill«tin 

 above mentioned.) 



Hopkins, in his " Soil Fertility and Permanent Agri- 

 culture," makes the statement that, under good farm 

 practice, roughly an amount of potassium equal to one- 

 fourth of one per cent of the amount contained in the 

 surface seven inches becomes available in a growing sea- 

 son. On this basis nearly all Kentucky soils contain 

 enough potassium for very large or maximum yields of 

 crops. For example, one hundred bushels of com, in- 

 cluding the stover, require 70 to 75 pounds of potassium. 



On the average, three-fourths of the potassium re- 

 quired to produce the grain crops is in the straw and 

 stalks. Nearly all the potassium in the feed given ani- 

 mals is returned in the manure. Hence with either live 

 stock or grain farming, if the supply of organic matter 

 is kept up by the return of the crop residues and ma- 

 nures, most of the potassium used by crops finds its way 

 back to the soU, and is readily available itself, while the 

 decay of the organic matter returned liberates more from 

 the minerals of the soil. 



Let us see if field tests show what the potassium 

 content of the soil would lead us to expect. On a lime- 

 stone clay soil at Bumside, Pulaski county, Kentucky, 

 where we have been conducting experiments for six 

 years, the following results have been obtained : 



Yields Per Acre — Bumside Experiment Field. 



Treatment. 



O 3 



a 3 

 Opq 



Oft 



oM 



m J?. 





<D U 



S-l M CJ 



°'B< 



■M-M 



03 (4 Fh 

 O (1) <U 

 OfaP4 



d o 

 !> ^ 



^ c8 



Rock Phosphate and Potash. 



Nothing 



Acid Phosphate and Potash- 

 Acid Phosphate _ 



Nothlng^ (See explanation) ... 

 Potash - - - 



3.8 

 9.0 

 14;3 

 17.7 

 20.4 

 11.9 



9.3 

 9.0 

 11.9 

 13.6 

 14.0 

 10.5 



2436 



2168 



32.9 



9.5 



45.7 



43.5 



1292 30.3 



764,17.6 



I 



1688 

 628 

 2272 

 2112 

 1176 

 560 



11.9 

 2.5 

 19.2 

 18.1 

 5.1 

 1.7 



?26.10 

 0.00 



25. W 

 0.60 

 0.00 



16.50 



(61.20 

 24.73 

 S4.»!!> 

 S5.09 

 65.42 

 31.37 



$10.37 

 0.00 

 33. £G 

 50.76 

 0.00 

 —9.86 



This soU contains 12500 lbs. of potassium per acre 

 7 inches, which is about half the average for the State. 



