ECOLOGICAL REACTION OF CROP YIELDS 



335 



By this horizontal shift the curve for the influence of the air is found as 

 the envelope A of the curves for the seven profiles. Because, however, not 

 only a horizontal, but also a vertical shift is necessary, a relation with the 

 second growth factor has to be taken into account. This relation is given 

 by formula 1.4 which shows, that the logarithm of the yield has to be taken 

 as vertical scale in order to obtain an additive relation between two growth 

 factors. 



The difference between the right-hand end of the curves and the envelope 

 in Fig. 8 now gives quantitative information with respect to the second 



Yield differences 



Variation in ground-water level 



Fig. 8. The envelope A of the curves, after shifting to part coincidence, depicts the 

 influence of lack of aeration. The deviating branches, depicting the influence of water, 

 give the influence of the factor water separately if subtracted from the envelope when, 

 according to formula 1.4, the yield is first plotted logarithmically. 



growth factor, which obviously is the factor water. These curves are given 

 in Fig. 9. In order to fmd out whether in this case also an additive relation 

 according to formula 1.5 is present, the logarithm of the yield deficit, 

 represented in Fig. 9, was plotted against the logarithm of the water depth. 

 Figure 10 depicts the result. If here the water depth was the exact growth 

 factor, than the hues should, according to formula 1.5, not only be parallel, 

 but also straight. The first is true, the second point, however, is not. By 

 shifting the hne in an oblique way they coincide fairly accurately. The 

 reaction curve B shows how the growth factor water correlates with the 

 logarithm of the water depth. If the logarithm of the vertical co-ordinates 

 of curve B is determined with the horizontal asymptote of line B as zero 

 point, and plotted against the logarithm of the Vv^ater depth, then a straight 

 line is obtained, showing that the growth function for water is an exponen- 

 tial function of the groundwater depth. This means that a close parallel 

 exists with the capillary movement, which might be expected. 



