248 IRRIGATION PRACTICE 



the right time of applying water to grain is to keep the 

 soil approximately at the same moisture content through- 

 out the season, until ripening sets in. Some authorities 

 have declared that plants need a high soil-moisture per- 

 centage at one period and a smaller one at another period 

 and so on throughout the season. This may be correct, 

 but in practice the farmer will make no mistake in main- 

 taining the soil in approximately the same correct mois- 

 ture condition throughout the season. More water will 

 be transpired, and the irrigations therefore heavier or 

 more frequent at the time of most rapid growth, that is, 

 about the time of flowering. 



It is seldom necessary to give wheat more than three 

 irrigations except, possibly, in the hot climate of Arizona 

 and similar regions. In fact, two irrigations are usual, and 

 one irrigation ordinarily ample wherever the annual 

 precipitation is between 12 and 15 inches. Where the 

 annual precipitation is large, little water will be required; 

 where it is small, much water must be added by irriga- 

 tion. Bark found that under a rainfall of about 18 inches, 

 the water used for grains by farmers during the months 

 of May to August inclusive, was as follows: May, 7.86 

 per cent; June, 52.34 per cent; July, 36.14 per cent; 

 August, 3.66 per cent; total, 100 per cent. In the moun- 

 tain country, where grain is sown in April, there is little 

 need of irrigation after late June or earliest July. Fall- 

 sown grain, with proper tillage, needs probably only one 

 heavy irrigation, or at the most two light irrigations. 

 McLaughlin recommends that wherever weeds have been 

 troublesome the grain fields be irrigated after harvest, to 

 germinate the weed seeds, and later to plow the plants 

 under. Thus, the soil is fertilized and the weeds destroyed. 



157. Quantity of water for wheat. The quantity of 



