100 Report of Farmers' Institutes 



" The sulphates * * * will not, in all probability, have the 

 same general crop-producing power as the phosphates, because of 

 the difference in the effect that the two acid radicals have on soil 

 jflora." 



CHEMISTRY, SOILS AND FERTILIZERS 



A neiv test for soil acidity. (Wis. 249.) Simplicity, accu- 

 racy and reliability in comparatively untrained hands are claimed 

 for this test. It rests on the principles that acids will set free 

 hydrogen sulphide gas when they act on zinc sulphide, and that this 

 gas will blacken, in proportion to the amount evolved, a paper 

 soaked in lead acetate. The reaction is thus a postive one easily 

 judged by the eye and the discoloration compared with a stand- 

 ard; so that a very reliable indication is given not cnly of the 

 presence of acid, but of the amount in the soil. 



Value of different sources of phosphorus. (R. I. 163.) This 

 bulletin discusses three experiments, extending over six, seven and 

 twenty years respectively, in which various sources of phosphorus 

 for improving soil fertility were compared under varying condi- 

 tions. 



In the first, or six-year test, ground bone, guano and dissolved 

 rock phosphate produced yields in the order mentioned, each less 

 than the one above by about 300 pounds, or nearly 4 per cent. The 

 phosphorus was provided in equal amount by each material, and 

 the nitrogen and potash in the guano were balanced by supple- 

 ments of nitrate of soda and muriate of potash added to the bone 

 and rock. Some of the soils were too acid to give the best yields 

 of all the crops grown. 



In the seven-year test results were held to be inconclusive, since 

 the phosphorus supply was not the only controlling element of 

 plant growth. 



The third experiment ran for twenty years, on limed and im- 

 limed soils, the phosphorus being made equal in cost on the differ- 

 ent series for five years, then gradually changed to equal weights, 

 a condition secured in three years. During the last ten years no 

 phosphorus was added, in order to allow study of the residual effect 

 of the previous applications. 



At the end of the equal-cost period the different sources had 

 given yields in the following order, from highest to lowest : Thomas 



