Jan. 1908.] 



39 



Scientific Agriculture. 



upon a result obtained by the Experimental Department. By several years' tests 

 they have shown that the order in which these grains should be sowed is, first 

 wheat, second barley, third oats, and lastly peas. And in testing six different dates 

 of seeding at intervals of one week, they have shown that for wheat and barley the 

 first sowing is the best, but for oats and peas the second, Temperature is undoubt- 

 edly one of the factors producing this result. This question and that of soil 

 moisture are very intimately related. A wet soil is a cold soil, but a dry one is a 

 warm one. The seed bed of a well-drained, well-tilled soil will be from 5° to 15° 

 warmer than that of a poorly drained, poorly tilled one. The reason for this is 

 found in two facts : (1) The behaviour of different substances toward heat. It is 

 more difficult to raise one pound of water one degree in temperature than one pound 

 of any other substance in the soil. The same heat would warm dry sand 10°, dry 

 clay 7°, dry loam 7°, dry muck or humus 5°, would warm the same weight of water 

 only 1°. This may easily be proven. Take a pound of water and a pound of sand at 

 the same temperature. Heat the sand 11° and put it in the water. The temperature 

 of the ; water will rise 1°, the temperature of the sand fall 10°. Again, take two 

 samples of the same soil, one saturated, that is, holding all the water it can, the 

 other half saturated. The heat that will raise saturated loam 3° will raise half 

 saturated loam and, by the way, a half saturated soil is in about the best 

 condition for tillage, for germination, and for plant growth. Hence, from a tem- 

 perature standpoint, you can see how essential it is that the soil should not be too 

 wet. (2) Evaporation cools the soil. That this is so I can prove to you in this simple 

 way. Here are two thermometers. They both read 67°. Here is a wet linen sack 

 that just fits the bulb. One would think it should be the same temperature as the 

 thermometers, for all have been lying here side by side. I slip the wet sack on one 

 thermometer and watch the result. The wet bulb reads 50°, i.e., 8° lower than the 

 dry bulb. These readings would vary for different conditions. The only possible 

 cause for this phenomenon is the evaporation from the gauze. The heat from the 

 thermometer is going into the gauze and into the water and evaporating the water. 

 You may take a certain amount of water and heat it from freezing point to boiling 

 point. You cannot make the water any hotter, yet the flame is sending more heat 

 into it all the time. What is becoming of that heat ? It is being used to turn the 

 water into vapour, or steam, as we say. It takes 5-35 times as much heat to turn 

 the water into vapour as it does to heat it from freezing to boiling. In evaporation 

 the same thing is true, only, since there is no fire to supply the heat, it must come 



rom the water itself, and hecce the water is colder than the surrounding air. The 

 very same phenomenon occurs wherever evaporation takes place. Hence, the 

 sooner you get that dry blanket of soil on the surface and check the evaporation, 

 the sooner will that soil become warm and suitable for seed-germination and plant 



growth. 



A third soil factor in crop production is the proper supply of air. Whether 

 the roots actually breathe this air as the leaves do has never been decided, but the 

 fact remains that they can no more do without it than the leaves cau. But absolute 

 exclusion of fresh air occurs only when the soil is,filled with water. Soils in a good 

 state of cultivation permit sufficient change of air for all our crops but the legumes. 

 We have been testing this point both last year and this year, and that is the 

 conclusion we have arrived at. Peas, beans, clover, cow-peas, vetches, etc., would 

 all be benefited by more air than reaches the roots under ordinary conditions. This 

 may explain why peas do so well on sod ; the soil is open in texture and allows much 

 interchange of air. 



Perhaps it may be interesting to note some of the agencies that promote 

 aeration. First, there is change of temperature of the soil. The air in the soil 



