420 REPORT OF THE COMMISSIONERS OF 



CONSUMPTION OF WATER BY GROWING AGRICULTURAL CROPS. 



In a paper, Recherches sur I 'Evaporation du Sol et des Plantes, Risler has given the 

 results of further experiments at his estate in Switzerland, extending considerably the 

 data of the paper already cited, his experiments being carried out specially with 

 reference to ascertaining the mean daily consumption of water by growing agricultural 

 plants, as well as by vineyards and two kinds of forests. * 



The following matter relating to Risler's experiments is condensed from 

 Ronna's Les Irrigations: 



" By way of confirming the results of investigations as to the water consumed by 

 growing plants, etc., carried out at the Agricultural Experiment Station of Rothamsted, 

 England, Risler has shown the different methods employed by him in 1867 and 1868. 

 By a continuation of these experiments in 1869—72, he has shown the mean daily 

 consumption of water by lucerne, wheat, oats, clover, meadow grass, etc. One of his 

 interesting conclusions is that winter wheat would have consumed daily, from April to 

 July, 1869, o. 10 of an inch of water per day for 101 days, or over ten inches for the 

 growing season. The experiments on water content of soil show that for the year 

 1869, the crops must have taken a small amount of water from the ground which, with 

 the rainfall, was sufficient to produce a satisfactory crop for the meteorological 

 conditions prevailing that year. 



"For oats there was needed in 1870, according to Risler, a quantity of water 250 

 times the weight of dry material contained in the crop. In 1871, clover transpired 

 263 units of water to produce one unit of dry substance, and English ray-grass 545 

 units of water for one unit of hay containing fifteen per cent, of water. For this last 

 the quantity of water corresponds to 0.276 inches in depth per day. 



" Risler observed, furthermore, that, following rains or wettings, transpiration of 

 plants increases, gradually diminishing in proportion as dryness increases, other 

 conditions remaining equal. When the water given off by the leaves is less than that 

 taken up by the roots, growth is active, while under the contrary conditions, plants 

 wither. 



"In a general way, the consumption of water by plants is more regular in clay soils 



than in sandy. Hellriegel states that in a sandy soil plants begin to suffer from 



drought when the soil does not contain more than 2.5 per cent, moisture. Risler finds 



that the approximate limit for clay soils is ten per cent., although in clay soil part of 



the water escapes absorption by the roots." 



* Risler's experiments as detailed in the two papers cited may be taken as classical. Apparently 

 they are the most thorough determinations thus far made. They are quoted with approbation by 

 Durand-Claye in his Hydraulique Agricole et Genie Rural, and by Ronna in his recent work, Les 

 Irrigations, and by other foreign writers. They have also been quoted by various American writers, 

 but, so far as known to the author, the original papers have not been much studied in this country. 



