REPORT OF THE CHEMIST 



151 



SESSIONAL PAPER No. 16 



From those figures we iiiul that last season, though June had one inch more rain 

 than the average, July was 2-72 inches and August -78 inches below the average for 

 these months, so that the total precipitation for the three months was 2-46 inches less 

 than the average. July had the lowest record in eleven years. 



Series I. Comprised 3 plots side by side in the plum orchard. The first plot or 

 strip was in what might be termed permanent sod, that is, it had been established for 

 a number of years. The second strip was cultivated three times during the early part 

 of the summer. The third plot carried mulching material, put on to kill bindweed, 

 to a depth of from 6 to 8 inches. This material was corn stalks, asparagus tops, old 

 hay, &c. The soil of this part of the orchard is light and sandy. 



Plot 1. — At the time of the first collection of samples there had been a period of 

 almost three weeks of extreme dryness and many crops were showing signs of suffer- 

 ing. The soil under the sod (Plot 1) was almost like powder; there was practically 

 no cohesiveness between its particles. The grass had formed a thick tough sod and 

 the growth of grass made in the spring had been cut on June 9. This mowing was 

 not at all severe, that is close, and the cut grass (a light crop) was not raked off. 

 This of course soon, dried into hay, but as it had not been spread evenly over the cut 

 area — and further was too light to act as an efficient mvdch, it is not a matter of sur- 

 prise to find that it had had no effect in checking evaporation. The data show but 

 3-65 per cent water — an amount frequently exceeded in laboratory air-dried soils, and 

 certainlj' very much lower than the minimum requisite for satisfactory crop growth 

 ^or indeed in many instances for the maintenance of plant vitality. The heavy loss 

 of moisture that had taken place was not entirely caused by the tran.spiration of the 

 grass, but was no doubt largely due to surface evaporation, which had been increased 

 by the establishment of capillarity. In undisturbed soil, bearing a crop, as for in- 

 stance that in sod or upon which grain is growing, the loss of moisture from this cause 

 is usually much greater than that by a transpiration of the crop — and especially is 

 this true of loams containing much coarse sand. 



Two weeks later, August 1, the moisture content was 5-03 per cent. As on the 

 day previous to the collection of the sample there had been a rainfall of -6 inch, the 

 increase over that present in the soil on the ISth is readily understood. 



On August 15, the date of the third collection, this soil contained 3-79 per cent 

 \?ater — an amount practically identical with that of six weeks earlier. The losses by 

 evaporation and transpiration we may therefore suppose had been supplied by water 

 drawn from lower depths than 14 inches and by rainfall — and thus in a large measure 

 an equilibrium maintained. That evaporation from the surface of the soil rather 

 than transpiration through .the foliage was the chief cause of loss of moisture is, I 

 think, made clear from the fact that the grass was not functionally active — that is, 

 was not making any appreciable growth — practically during the whole period of this 

 investigation. 



Series I. —Conservation of Soil Moisture, C. E. F., Ottawa, Ont., 1906. 

 (Samples collected to a depth of 14 inches.) 



Precipitation from July 1 to July 18. 



