263 STATE BOAKD OF AGKICULTURE. 



destitute of yegetable mold. Many Iiave also observed that the use of plaster 

 rapidly exhausts the soil of its vegetable matter. All have noticed the dark 

 green color which plaster Tinder favorable conditions imparts to growing plants ; 

 also the marked tendency to the formation of leaves and vegetable fibre without 

 a corresponding tendency to the formation of flower and seed. Now these are 

 the characteristic indications of a large dose of ammonia. It is well known 

 that the vegetable matter of soils contains a large amount of combined nitrogen 

 (about two per cent.), but it is what is called inert nitrogen. If this inert 

 nitrogen of vegetable mold were made active, it would afford a large amount 

 of a very important material for the rapid development of the plant. 



Placing all these facts together, the question arose in my mind, does plaster 

 afford an increased supply of nitrogen to plants by reacting upon the vegetable 

 mold of the soil, setting free its inert nitrogen hi an active form ? To test this 

 matter I weighed out two equal quantities of the same swamp muck, placed one 

 in a given measure of solution of plaster, the other in the same quantity of pure 

 water. These two specimens were placed side by side, stirred up occasionally, 

 and after a Aveek a quantity of water was filtered off from each, and the solu- 

 tions carefully tested for ammonia. This experiment I have repeated, and with 

 results nearly uniform. The plaster water always gave decided indications of 

 ammonia, while the pure water with muck either gave no indications of ammo- 

 nia or very feeble ones. 



From the similarity of effects on plant life of plaster and ammonia, from the 

 fact that plaster is without such influence in the absence of vegetable mold, and 

 from the fact that solution of sulphate of lime sets free ammonia when brought 

 in contact with vegetable mold, I am led to believe that one of the most impor- 

 tant properties of ])laster is its power of making active the inert nitrogen of the 



vegetable matter of soils. 



LOSS BY DRAINAGE. 



We must not close our consideration of this subject without calling to your 

 mind the important fact that a good deal of plaster is every year removed from 

 the soil by the action of water. Plaster is a com.paratively insoluble material, 

 but it dissolves in 500 parts of water. In consequence of this solubility, and of 

 the fact that the soil has no power of fixing this substance in an insoluble form, 

 all river water in this State contains this material, and it is constantly being 

 washed out of the soil. While the amount of plaster held in solution in any 

 small specimen of water is small, yet the aggregate thus removed by our rivers 

 is large. A small stream flows through the college grounds, which is dignified 

 by the name of Cedar river. I have measured the stream and estimated its 

 average flow, and the amount of jilaster it holds in solution. I find the stream 

 80 feet wide, two feet deep, and the flow two miles an hour. I made two sep- 

 arate estimates of the amount of plaster held in solution in a cubic foot of 

 water : by the first estimate it held 13 grains in each subic foot ; by the second 

 estimate, 12.9 grains. These estimates agree very closely. But during the 

 spring floods the river water will contain less plaster than I have estimated. 

 Let us call the average ten grains of plaster to tlie cubic foot : how much plas- 

 ter will this small stream annually carry away from the small section of this 

 State which it drains? More than ten thousand tons a year! If this small 

 stream carries off such an enormous amount year by year, how much will all the 

 rivers of our State remove yearly? 



You may ask what becomes of all this plaster? It is carried finally into the 



