Jan. 1908.J 



37 



Scientific Agriculture, 



be beneficial, provided, of course, that the subsoil is left in the bottom of the furrow, 

 as demanded by other conditions. It should be said here, however, that there are 

 some soils, e g., light sandy loam, which do not admit of loosening up to any great 

 extent, for being of coarse texture they dry out very rapidly when loosened up. 

 We may infer also that lands with open subsoils (not too open, of course,) will have 

 greater reserve of water for the plants in time of drought than will those with 

 close subsoils. And we might hence inquire if there is any means of improving the 

 texture of subsoils of the latter class. In this connection we recall that it is a 

 matter of common experience that well-drained soils will withstand a drought better 

 than similar soils not so well drained, although the crops on both might look 

 equally well at the commencement of the drought. This result, which, at first 

 thought might not be expected, finds its explanation in the fact that the drainage 

 always improves the texture of all the 3oil affected, subsoil as well as surface soil, 

 and with improved texture the water-retaining capacity is increased. Thus, when 

 the soil is in best condition for supplying water to the crops in a dry season, 

 it is likewise most capable of protecting them during a wet one. 



But there is another aspect of soil moisture that during seasons of average 

 or scant rainfall is equally as important as that already considered, viz., the 

 conservation of the water after it has been stored in the soil. The one great source 

 of loss is evaporation. Few, I believe, have any conception of how much water may 

 be lost in this way. We have had the good fortune to devise a reliable apparatus for 

 measuring the amount of evaporation from water sui'faces, and have been making 

 continuous tests since the middle of May, and I must eonf es3 that we have been 

 surprised at the results. The College reservoir, which you have all seen, is approxi- 

 mately 100 feet by 60 feet and 12 feet deep. How much water do you suppose 

 evaporates from that reservoir per day, on an average, from May to October? Most 

 people guess in gallons, and when we suggest barrels they look incredulous ; yet it is 

 a fact that on an average during that whole period twenty barrels a day were lost by 

 evaporation, a depth of one-fifth of an inch. The greatest loss on any one day was 

 fifty barrels, which occurred between 6 o'clock on the evening of August 24th and 

 6 o'clock on the evening of August 25th. The three days preceding had been 

 excessively warm, but about 4 o'clock on the 24th the temperature dropped suddenly, 

 and a very strong wind rose which continued throughout the night and the 

 following day, 



In measuring the evaporation we use a graduated glass standpipe of water 

 which feeds automatically into an evaporating cup, so arranged that the wind 

 cannot blow the water out, although the evaporating surface is level with the top 

 of the cup. The amount that has passed out of the standpipe gives the depth of 

 water evaporated since last observation, and from this we can calculate the amount 

 in barrels. When we have another season's work on this and on evaporation from 

 soils, we hope to publish a detailed report of our methods and our results. 



An evaporation of twenty barrels a day from an area 100 feet by 60 feet is equal 

 to about 140 barrels per acre. The amount will, of course, vary with the situation, 

 exposure, temperature, etc. What the exact loss from soils would be during that 

 period we are not yet in a position to say, that problem lies all before us ; but, from 

 preliminary tests, we have reason to believe that so long as the soil is bare and looks 

 moist on the surface, evaporation is robbing it of its moisture about as fast as it 

 takes water from the reservoir. But as soon as the soil looks dry, or is hidden by a 

 crop, the rate of evaporation falls off very rapidly. 



These latter conditions are best brought about by cultivating and seeding as 

 soon as the land is dry enough. If there are two plots of soil side by side, and one 

 is cultivated and the other is not, the evaporation from the cultivated one is much 



