Rothamsted Symposium on Trace Elements 



102 



Swede C^rassica napus v. na^pohrassica).— Brown heart of 

 swede is common in the central and southern parts of Finland. 

 It is found on different mineral soils as well as on peaty soils, and 

 it is most severe in fields which have been continuously and amply 

 fertilized with mineral fertilizers. Both in swedes and in sugar 

 beets the boron deficiency diseases are found on acid soils. In 

 most cases the pH figure of the soil was under 6. The lowest pH 

 of the soil where the disease was found was 4.34. The fields in 

 Finland are, as I already mentioned, on the whole acid, so that 

 only a small number of the brown heart cases investigated were 

 found on soils with a pH of over 6. 



Table 21 : Liming experiments in 1938-1939 on light clay: — 



Plots 



OF 



SOIL 



IN 1938 



Yields of roots^ 



Yields of tops* 



Without With Without With 



boron H3BO3' boron HaBOj' 



— 100 142 100 154 



Checki 5.17 149 183 165 261 



1- 2000 CaCO, 5.45 151 190 175 262 



h 4000 CaCOa 5-54 127 190 152 268 



|-8000CaCO3 5.94 113 197 100 284 



1 900 kg of superphosphate, 500 kg of potash salt, 40%, and 750 kg nitrate of lime per hectare. 

 ' The average yields of two years given in relative numbers, as compared to the yields of 0-plots without 

 boron, of which 10.470 kg per hectare was given to roots, 13.460 kg per hectare to tops. 

 'In 1938 8 kg boric acid per hectare was used, in 1939 li kg. 



Virulence of brown heart varies considerably in different years, 

 even in one and the same place. In some years, most of the 

 swedes grown will be affected while in other years only a few 

 cases are found. It cannot always be attributed to climatic con- 

 ditions. 



Affle (Fyrus waZws).— Internal cork in apples is, together with 

 heart rot and brown heart in swedes, the most common boron de- 

 ficiency disease in Finland. At the Department of Plant Path- 

 ology Laboratory the disease has been under close observation since 

 1930. It is found everywhere where apple trees are grown in 

 Finland. Usually only a few trees in orchards are affected by this 

 disease, but in some years it can be rather common. In 1947, for 

 instance, the disease was more common than usual which was 

 obviously due to the unusually dry summer. 



