362 W. C. VISSER 



Groundwater Depth and Cropping Pattern 



In areas with a shallow water table, the question arises what influence the 

 raising or lowering of the water table will have on the crops which one 

 may expect will be grown. 



In a sandy area differences in groundwater level promised workable data 

 for an intended investigation. The crops grown on the fields of some 70 

 farms during the last five years, as well as the water table in summer, were 

 estabhshed. These data suppHed the frequency curves for each crop. In 

 Fig. 4 the curves for a number of crops, plotted against the groundwater 



Frequency*/' 

 70 



RYE (+) 



Mean depth of ground-water table in summer 



J I ly o I 



250cm minus soil surface 



Fig. 4. For sandy soil and small farms the crop frequency has been determined and 

 plotted against the groundwater depth in summer. Grass is clearly a wet-land crop, 

 rye grows on dry fields and potatoes have an intermediate position. 



depth are given. The difference in position of the crops in the cropping 

 pattern is apparent and a change in groundwater depth will influence the 

 type of farm considerably. 



The data are fitted around a parabola by horizontal and vertical shifts. 

 In Fig. 5 the result is given. For each crop the horizontal axis is given with 

 endpoints 50 cm and 250 cm groundwater depth and this axis is drawn at a 

 frequency value of 10%. Where the shifted horizontal axes are situated 

 well above the parabola, this means that at optimum conditions the 

 frequency of occurrence remains below 10%. The cropping system with 

 respect to the influence of water is for every crop given by the parabola 



