Jan. 1908.] 35 Scientific Agriculture. 



intervals as necessary. The results were as follows :— 



Table Showing Rainfall and Depth op Water in Inches used by 

 Crops during a Dry Season. 



Crop. 



Depth of rain 



while crop 

 was growing. 



Depth of 

 water added. 



Total depth 

 of water vised 

 by crops. 



Total depth 

 compared 

 with rainfall. 



Wheat 

 Peas 

 Barley 

 Oats 



10-51 

 12-50 

 7-91 

 7-91 



12-09 

 14*88 

 10-61 

 13 24 



22-60 

 27-38 

 18-52 

 21-15 



2-15 

 2-19 

 2 25 

 257 



That is, these crops, during their period of growth, used approximately two- 

 and-one-quarter times as much water as fell in rain. Since the plants did not grow 

 as large or strong as those in actual field conditions, we are safe in assuming that 

 field crops used as much as or even more than those in the crocks. Last season was 

 about an average one. Thus we see that under ordinary conditions, if the crops are 

 to be supplied with all the water they need, there must be a great store of it in the 

 soil from which they may draw. Hence, in anticipation of an average or dry season, 

 our treatment of the soil must put it in such a conditiou that it will retain a great 

 deal of the spring, winter, and autumn precipitation. The crocks in 1905 were set 

 on the root of the annex to our building during the early part of the season ; but it 

 was thought that possibly the loss there was very much in excess of what it would 

 be at the ground. So about the middle of the season half the crocks were removed 

 to the garden, part being set on the ground and part in the ground about level 

 with it. Between the losses from the former and the latter, the scales showed no 

 difference, though the loss from those on the roof was slightly greater than from 

 those in the garden. But the first tests in any experiment are seldom made in just 

 the same way as subsequent ones. This season (1906) all crocks were set in the 

 ground in a field of barley, a path leading into the grain, and the crocks being set 

 back in it on either side of the path. 



The crocks had a capacity of four gallons, were 10 inches in diameter, and 

 about 12 or 13 inches deep, and caught all the rain that fell. The day they were set 

 outside a very heavy rain fell, and having weighed them just before the rain, we 

 weighed them again just after, and compared the result with our rain-gauge, It 

 was found that the crocks had absorbed the whole shower. None of the rain was 

 lost by drainage. We had a drainage tube in the bottom of each crock, but not 

 once during the whole season was the rain sufficient to saturate the soil and cause 

 percolation. The quantity of rain required to saturate the soil depends on the 

 amount of moisture in the soil when the rain comes. We tested that point once 

 during the season. We let the soil dry out until the grain began to wilt. The 

 amount of water in the soil at wilting point varies in different soils. This was a 

 loam, and by actual test was found to contain 7'3 per cent, water when the plants 

 wilted. Water was added to the crocks until it began to run out of the drainage 

 tube. When percolation had just ceased, they were weighed again, and it was 

 found that to saturate the soil whichwas nine iuches deep, it required two-and-one- 

 half inches of water. That is, in time of drought when your crops begin to wilt 

 it would require a rain of two-and-a-half inches to saturate the soil nine inches deep. 

 That explains why it takes so much rain to " break the drought." In all our records 

 here we have no such rain in 24 hours. Only two or three times have we had as 

 much as two inches. A rain of one-and-one-quarter inches would saturate the soil 

 four one-half inches deep, but gravity and capillarity would carry part of the 



