4G6 Abstract Report of Afjricultural Discussion?.. 



The nitrates, wliicli invariably occur iu all drainage-waters, and wLicli 

 are also found in all natural spring-\Yaters, arc evidently the in'oducts 

 of the oxydation of organic matter originally i)resent iu the soil. 



There is a wise j^rovision that no organic filth shoidd accumulate. 

 The air which is carried down in the water, bringing oxygen into 

 immediate contact with those organic remains, destroys them, and 

 converts an obnoxious material into one that is of the greatest 

 value. 



The change which water produces on a variety of mineral matters 

 is no less important. I just now observed that all natm'al water (rain- 

 water as well as spring-water) invariably contains carbonic acid iu 

 solution. This carbonic acid acts as a solvent for many mineral 

 matters whicli are insoluble in pm'c water. Coming from rocks that 

 contain small quantities of phosphate of lime, it dissolves this im- 

 portant constituent, and renders them available for the use of the i)lants. 

 Again, water charged with carbonic acid decomposes some of our 

 natural silicates, and renders them available as plant-food. Lastly, water 

 carries wai'mth into the soil. It is well laiowu to all scientific men 

 that water is heaviest and densest at 40^ — that is 8^ above the freezing 

 point. When the air is at 32^, the water as it cools, instead of 

 becoming denser and sinking, actually rises in the uj^per layer of the 

 soil; the colder particles of water rise higher until they are at 32^, 

 when a sheet of ice is formed, wdiich preserves the water below at 40^, 

 so that xmder ice the tcmpcratm-e of water is at least 8^ higher than 

 that of the air dmung frost. 



On an average, perhaps, the temperature of our natural spring- 

 waters may be said to be about 10-' above that of the air dui'ing 

 the months in v.hich irrigation is practised, though we find in 

 them great variations. Some that feel cold during the summer, 

 and warm during the winter, -when tested with a thermometer 

 will be found of a uniform teuiperature throughout the year ; they are 

 not affected by the temperature of the atmosphere. I take it that such 

 waters, other circmustances being equal, arc particularly useful for 

 irrigation, as they convey into the soil and to the roots of the jdants a 

 considerable degree of warmth. These may be said to be some of the 

 chief benefits that arise, speaking generally, from the percolation of 

 water through tlie soil. 



I now pass on to speak more especially of the most desirable 

 qualities of water used fur irrigation. I will take them in the 

 order in which they arc usefid to the fanner. The best water for 

 in-igation is no doubt sewage-water ; because it is a natural water, 

 which contains refuse excrementitious matters, that are exceedingly 

 useful fertilising agents. In no natui-al waters do we find the amount 

 of ammonia or of phosphoric acid that occurs even in the most dilute 

 sewage; and as ammonia and phosphoric acid, perhajjs also potash 

 (which occurs in sewage in appreciable quantities), are fertilisers of 

 the greatest importance, we ought not to waste them, but apply 

 them to the land, if possible. The organic matters, in percolating 

 through the soil, are converted into nitrates, the gTeater portion of 

 which, no doubt, is rapidly taken up by the succulent produce which 



