LySIMETER JJ^XPERIMENTS 



33 



It seems very likely that the conditions were less favorable for 

 evaporation in the European experiments than in the writers', and that 

 the reason for the greater percentage percolation in these experiments 

 is due to the large winter percolation, as has already been explained. 



SUFFICIENCY OF MOISTURE SUPPLY FOR CROP GROWTH 



The thoro drainage to which soils in the lysimeter tanks are subjected, 

 suggested the possibility that there might be a deficiency of moisture 

 for crop growth at some time during the growing season and that a limiting 

 factor might thus be introduced. Provision was made at the time the 

 tanks were constructed by which the water could be held in the tanks 

 in the spring at any desired depth, and thus a reservoir of water be held 

 for use of the plants during the active growing season. This was not 

 used the first year because it was desired to ascertain whether it was 

 needed. There was no evidence that it was, nor have subsequent crops 

 appeared to need more moisture than was available. 



It is usual for water in the cropped tanks to cease percolating in mid- 

 summer, but this does not necessarily mean that the soil is too dry to 

 furnish all the moisture that the crops need. The yield of maize was 

 exceptionally heavy the first year the tanks were planted. The large 

 yield was probably due in a measure to the thoro aeration which 



TABLE 15. 



Average Yield of Crops by Years on Tanks 1 to 12, Expressed in 

 Dry Matter per Acre 



33 



