CROPPING PATTERN AND WATER RELATIONS 



W.C.VlSSER 



Instituut voor Cultuurtechniek en Waterhuishouding, 

 Wageningen, Netherlands 



Aim of the Investigations 



Water relations in the field not only influence the yield of crops, but also 

 the kind of crops the farmer wiU grow. On dry soils rye is planted fre- 

 quently. But if the water relations are improved and a larger yield per ha 

 is obtained, there is, however, a good chance that the total amount of seed 

 produced on the farm will decrease. If the field is better provided with 

 moisture, this will induce the farmer to grow less rye and to increase the 

 acreage sown with beet and potatoes. If one tries to predict the result of 

 an increase in fertihty of the soil, it will not only be necessary to predict 

 the yield per unit area, but also the percentage of the area occupied by each 

 crop. This proportion of the different crops in the total farm area will be 

 called the cropping pattern. 



Nature of Problem 



Within rather wide Hmits the farmer is free to decide on what area of any 

 crop should be planted. For that reason the frequency of occurrence of a 

 certain crop is governed to a greater extent by the law of probability than 

 by some more definite agricultural rule or necessity. Since the ecological 

 situation will not be equally favourable however, not every crop will be 

 grown to a same percentage and with a same probabihty. The less optimal 

 this situation for a certain crop is, the smaller will be the probability of tliis 

 crop bemg chosen by the farmer. 



Generally it wiU be rather difficult to collect enough data to determine 

 the frequency of occurrence of the crops accurately. Every field gives only 

 one observation a year. Data for a number of years will be needed. But 

 the crops grown in earlier years are often not too well remembered and the 

 frequency data therefore will be less reHable. Moreover, cropping patterns 

 of former years are Hable to restrictions in comparability due to changes in 

 the economy of agricultural production. Data from more than five years 

 ago may become of suspect uniformity. 



The number of data for calculation of the frequency decreases still more, 



