188 THE YEAR-BOOK OF AGRICULTURE. 



constituents present in the soil, in a given time. From the same surface, there is thus ob- 

 tained, in that time, a heavier produce perhaps in one year as much as in two without this 

 excess of atmospheric food. 



47. In a soil rich in the mineral food of plants, the produce cannot be increased by adding 

 more of the same substances. 



48. In a soil rich in the atmospheric food of plants, (rendered so by manuring,) the produce 

 cannot be increased by adding more of the same substances. 



49. From land rich in the mineral constituents, we may obtain in one year, or for a series 

 of years, by the addition of ammonia alone, (in Its salts,) or of humus and ammonia, rich crops, 

 without in any way restoring the mineral substances removed in these crops. The duration 

 of this fertility then depends on the supply ; that is, the quantity and quality of the mineral 

 constituents existing in the soil. The continued use of these manures produces, sooner or 

 later, an exhaustion of the soil. 



50. If, after a time, the soil is to recover its original fertility, the mineral substances ex- 

 tracted from it in a series of years must be again restored to it. If the land, in the course 

 of ten years, has yielded ten crops, without restoration of the mineral substances removed 

 in those crops, then we must restore these in the eleventh year, in a quantity tenfold that 

 of the annually-removed amount, if the land is again to acquire the power of yielding a 

 second time a similar series of crops. 



> 



Weeds in Walks. 



THE following modes of preventing the growth of weeds in gravel-walks, are copied from 

 the correspondence of the London Gardener's Chronicle : 



In order to prevent weeds from growing on walks, put a layer of gas-lime under the last 

 inch of gravel. This also helps to bind the gravel. 



The following is the way in which I managed walks when I was a gentleman's gardener. 

 In one situation I held I had three miles of gravel-walks to keep in order. In winter, when 

 there was sufficient frost to freeze the gravel in the mornings, I employed the laborers in 

 cleaning the walks with a half-worn out birch-broom, sweeping backwards and forwards, and 

 then removing with a new broom what the old ones took off the surface. When the walks 

 were covered with moss, it was scraped off with a hoe before the broom was used. After 

 having pursued this practice for six years, my walks looked as fresh and clean as if they had 

 been newly gravelled. Last season very few weeds made their appearance during the sum- 

 mer ; by performing the operation when frost is on the ground, you not only remove all small 

 weeds, but you sweep off most of the seeds deposited there to vegetate the following summer. 

 If docks, thistles, or dandelions appear, cut out their crowns and put a little salt on them ; 

 you will not have to repeat the salting twice in one place. 



On the Composition of the Salt best Adapted for Dairy Purposes. 



THE nature of the salt best adapted for the dairy has long formed a subject of discussion 

 among dairy farmers, and many opinions, and not a few fanciful prejudices, exist regarding 

 it. It is well known that, for a long time, very decided opinions existed as to the superiority 

 of bay-salt, and at one time the imports of that variety of salt were considerable. Bay-salt 

 is produced in Spain by the spontaneous evaporation of sea-water, which at high-water is 

 allowed to run into shallow ponds, in which it is gradually concentrated by the heat of the 

 sun's rays. The salt so deposited is always in crystals of considerable size, and generally of 

 a brownish color. In spite of the color, it is a very pure salt, and contains but little of the 

 magnesian compounds present in the sea-water, which are entirely left in the mother-liquor 

 from which the crystals have been separated. 



Lime and magnesia especially the chloride of magnesia existing in salt have a very 

 powerful affinity for water, and retain it in considerable quantity. The chloride is even a 

 deliquescent substance that is to say, it absorbs moisture from the air ; so that a sample of 

 ealt containing it, even if artificially dried, will again become moist, if kept for some time. 



