212 SOILS. 



This is doubtless due, as King shows, to the equal thinness 

 of the moisture film remaining on the soil grains in either 

 case; the number of grains, and therefore the aggregate sur- 

 face holding these films, being much greater in the clay than in 

 sands ; hence the higher water content. 



It is interesting to compare these figures given by King for 

 clover and maize at the wilting-point, and fallow ground adja- 

 cent, with those given by Eckart ( Rep. Expt. Sta. Haw. Sugar 

 Planters' Ass'n., 1903) for those affording good growing 

 conditions for sugar cane on the (highly ferruginous) soils 

 of that station. The plots were irrigated at the rate of one, 

 two and three inches of water per week, allowance being 

 made for the rainfall. Two inches proved, on the whole, to 

 give the best average results for production. The moisture 

 determination of the soil under the two-inch regime gave an 

 average moisture content of 29.13% in the first foot of soil. 

 It is not stated what was the hygroscopic coefficient of that 

 soil, but it was probably very high; in the neighborhood of 

 2I -5% Judging by the determinations made with six 

 Hawaiian soils at the California Station. This would indi- 

 cate about 7.63% of free moisture as the optimum for sugar 

 cane. 



Moisture-requirements of Crops in the Arid Region. 

 Plants (particularly broad-leaved ones) which have made a 

 brash growth during a period of abundant moisture, will wilt 

 quickly when sunshine returns, and take some time to adapt 

 themselves to the drier conditions. On the other hand, plants 

 accustomed to dry air and scanty soil-moisture, will not wilt or 

 suffer under what would elsewhere be considered very rigorous 

 conditions. Loughridge * has made numerous determinations 

 of moisture in soils in which crops were beginning to suffer, 

 and others on similar soils that were growing normally, and 

 found that in general, not only were the differences in mois- 

 ture content considerably less than in the case above quoted 

 from King's observations, but that the amounts of free mois- 

 ture required by various crops in the arid climate of Cali- 

 fornia were surprisingly small. 



The tables below show the results of observations made by 



1 Rept. Cal. Expt. Sta. 1897-08, pp. 65-96. 



