Water Needed for a Given Crop 99 



it would be 1.54 inches. It is certain that there is a 

 further loss from these soils which is likely to be 

 nearly if not quite as large as that computed, and that 

 is the evaporation which takes place through the grain 

 after coming to maturity, while it is standing upon the 

 ground before being cut ; for it is known that the 

 movement of water through the plant does not stop at 

 once when the kernels have fully matured. Further 

 than this, if a considerable time intervenes between 

 the time of the first rains and the germination of the 

 seed, and especially if, after the grain comes up, it 

 for any reason makes an abnormally slow growth, there 

 will then be considerable additional losses which are 

 not included in the figures given in the table ; and it 

 would seem that the average necessary loss of soil 

 moisture from these lands which in no way contributes 

 to the growth of the crop of wheat may easily be as 

 high as 3 inches. If this be true, the figures in the 

 last column of the table would be nearer 7.5, 9, 10.5, 

 12, 13.5 and 15 inches, respectively, for the differ- 

 ent yields, than those stated. It is further probable 

 that for the lighter yields, where the grain would have 

 to stand thinner on the ground or else the plants be 

 smaller, there would be absolutely more loss of water 

 from the surface of the soil itself, and, hence, that the 

 lower figures just given are likely to be found larger 

 than they are there stated. 



The mean annual rainfall of the San Joaquin- 

 Sacramento valley, as given by Harrington in his rain- 

 fall map, ranges from 5 inches in the far south to 12 

 inches in the north, this amount all falling between 



