40 Irrigation and Drainage 



corn used water at the rate of 309.84 pounds of water per pound of 

 dry matter produced, and 25.74 inches of water when measured 

 in depth on the area occupied. But four trials with a variety of 

 flint corn gave a mean of 233.9 pounds of water per pound of dry 

 matter, which is 75.94 pounds or 32.5 per cent less than in the case 

 of the dent variety. This is not because actually less water was 

 used per unit area, for the flint corn in these four trials did use 

 a mean of 26.82 inches against 25.74 for the dent corn. 



It seems not improbable that this more economical use of 

 water by the flint corn may be in part due to its lower habit of 

 growth and the greater abundance of foliage closer to the ground, 

 for it may be expected that the lower position of the leaves, and 

 their crowding as well, would tend to lessen the amount of 

 evaporation in a given time. But to whatever the difference may 

 be due, it is plain that on light soils and wherever the water 

 supply is limited, larger returns may be secured by paying atten- 

 tion to the variety of plant grown. 



The amount of water used by a particular crop might be 

 expected to vary with the humidity of the season and the amount 

 of wind movement during the period of growth of the crop ; but 

 the data obtained do not appear to show so marked a relation as 

 would seem should exist. The mean relative humidity of the air 

 at Madison at 2 P. M., in 1891, for June, July and August, was 

 63.66 per cent, while in 1892, for the same time of day and period, 

 the mean was 68 per cent ; and the total wind movement for 

 Madison, these years, for the three months, as given by the 

 records of the Washburn Observatory, was 20,712 miles in 1891 

 and 18,870 in 1892. But in 1891, 26.39 inches of water gave a 

 yield of dry matter per acre of 19,845 pounds, and in 1892, 25.09 

 inches gave a yield of 19,184 pounds of dry matter per acre of 

 corn in the plant cylinders in the field. The differences in the 

 amounts of water used during the two years, it will be seen, is 

 very small, especially when it is recognized that in 1892 the dry 

 matter produced, and presumably the evaporation surface also, 

 was less than in 1891. 



So, too, in the case of oats for these two years, 19.60 inches 

 of water gave 8,861 pounds of dry matter per acre in 1891, and in 



