480 NINETEENTH ANNUAL YEAR BOOK— PART IX 



To make the litmus paper test, take a handful of wet soil and make 

 it into a ball. Break the ball in halves and insert a strip of blue litmus 

 paper. Press the halves firmly together, and allow to stand twenty 

 minutes. At the end of that time break the ball apart and examine the 

 paper. If it is pink, the soil is acid. If no change has taken place in the 

 color of the paper the soil does not need lime. This test, while it is fairly 

 reliable in determining the presence of acids, gives little indication as to the 

 amount of lime which should be applied. The Soils Section of the Iowa 

 Agricultural Experiment Station will test soils for their lime requirement, 

 by the Truog method, free of charge, and make recommendations as to the 

 proper amount of lime to use.* 



In collecting soil samples for the acidity test, care should be taken 

 to choose them from areas representative of the entire field. Clear the 

 surface of any vegetation and dig a sample to a depth of seven inches. Take 

 a sample of the subsoil from seven to 18 inches at the same location. Make 

 ten other samplings a few rods apart in the sarne manner and on areas 

 representative of the same kind of soil. All surface samples are then 

 thoroly mixed. About one pint of the mixture is placed in a bag, can, or 

 other convenient receptacle. The subsoil samples are handled in the same 

 manner. Both surface and subsoil samples should be labelled, securely 

 wrapped and sent to the Soils Section, Iowa Agricultural Experiment 

 Station, Ames, Iowa. 



KIXD OF LIME TO USE. 



There are four forms of lime but all of these cannot be recommended 

 for correcting soil acidity. 



Burned Lime is made by heating limestone to a red heat. As a result of 

 this heating a caustic lime is produced. 



Water slaked lime is formed when water is poured over burned lime. 

 This material hais a burning effect on plants if not properly applied. 



Air slaked lime is formed when burned or water slaked lime is ex- 

 posed to the air. 



T-ife three forms of lime mentioned should not be used for correcting soil 

 acidity unless completely slaked, applied in small amounts and allowed to 

 remain in the soil for some time before seeding any crop. 



Burned lime, water slaked lime or air slaked lime may be spread on 

 plowed land in the fall and by spring the material will have become suf- 

 ficiently slaked. 



Ground limestone is the most common and desirable form of lime to 

 use for agricultural purposes. It is made by grinding raw limestone rock 

 such as may be found in the quarries throughout the state. For best re- 

 sults, this material should contain 85 to 95 per cent carbonate with 60 to 

 70 per cent of the stone in a powdered form. 



Ground limestone is not considered a direct fertilizer but a material 

 to be used for correcting the acid condition which exists in many soils. 



*The Soils Section Is frequently called upon to make a complete analysis 

 of soils and fertilizers. At the present time tests can only be made for the 

 lime requirement of soils and the carbonate content of limestone, as no 

 appropriation is available with which to carry on indiviidual analyses for 

 nitrogen, phosphorus, potassium and other plant food elements. Complete 

 analyses of soils are made, however, in connection with the soil survey and 

 the results thus secured are published in reports for each county surveyed. 



