ON THE ESSENTIAL CONSTITUENTS OF MANURES. 31 



Report on Field Experiments and Laboratory Researches on the Con- 

 stituents of Manures essential to cultivated Crops. By Dr. AUGUSTUS 

 VOELCKEB, Royal Agricultural College, Cirencester. 



THE field experiments on which I have to report were begun in 1855, and have 

 been continued since from year to year. They were at first instituted chiefly 

 for the purpose of ascertaining practically the comparative economic value 

 of some of the artificial manures, such as guano, superphosphate of lime, 

 bone-dust, &c., in reference to root-crops. In the course of my experiments, 

 however, I was led to abandon, more or less, the primary object for which the 

 experiments were at first undertaken, and to make them subservient to assist 

 the solution of several disputed and important points in agricultural and 

 physiological science. 



Amongst other questions which arise in the mind of the agricultural 

 chemist who has closely followed the progress of agricultural chemistry, the 

 following are some of the more important : 



1. Can ammonia or nitrogenized matters be dispensed with in manures, or 

 is it desirable that there should be a certain proportion of nitrogenized matter 

 or ammonia in manures ? 



2. What is the effect of ammoniacal salts, of phosphates, of alkalies, and 

 other fertilizing constituents applied separately upon vegetation ? 



3. Is the practical effect produced by ammonia, or by phosphates, &c., the 

 same upon wheat or other grain crops as that produced upon turnips or clover? 



4. Are there fertilizing constituents which benefit certain crops more than 

 others ? 



5. Is it desirable or unphilosophical, and therefore leading to the ultimate 

 exhaustion of the soil, to apply special fertilizing matters to the land, f. e. 

 matters which contain but 1, 2, or at ail events a limited number of chemical 

 compounds ? or is it necessary, in order to maintain the permanent fertility of 

 the land, to restore to the soil in the shape of a compound and universal ma- 

 nure, all the constituents removed by the crops grown upon the land in pre- 

 vious years? These and other similar questions, affecting agricultural practice, 

 have occupied me for several years past. 



The results of my experiments detailed in the following Report, I trust will 

 be found useful contributions towards the final settlement of the mooted 

 questions. 



Field Experiments made in \ 855. 



Although I believe that the minute chemical analysis of soils, generally 

 speaking, affords but little or no indication as to the fertilizing matters which 

 are best calculated to improve their productive powers, I am still of opinion 

 that it is desirable and even indispensable to record in all field experiments, 

 the principal physical characters, and the amount of at least the chief or pre- 

 ponderating constituents of the soil of the experimental field. 



I would therefore observe that the experimental field was a naturally poor 

 shallow soil with clayey subsoil of inconsiderable depth, and resting on the 

 Great Oolite limestone rock. 



Submitted to a general analysis, it yielded 



Organic matter and water of combination 6*339 



Oxides of iron and alumina, with traces of phosphoric acid 9*311 



Carbonate of lime 54--5S6 



Magnesia 1 



Alkalies V determined by loss -837 



Sulphuric acid J 



Insoluble siliceous matter (chiefly clay) 28'94>7 



100-000 



