THE APPLICATION OF THE METHOD OF VISUAL 

 DIAGNOSIS TO TRACE ELEMENT PROBLEMS 



IN PLANTS 



hy T. Wallace, C.B.E., M.C., D.Sc, F.R.I.C, 



Agricultural and Horticultural Research Station, Bristol University, 

 Long Ashton, Bristol 



Introduction:— My interest in the application of visual meth- 

 ods to problems of the mineral nutrition of plants began in 1920, 

 when I commenced investigations on the nutrition of fruit crops. 

 Previous experiments by other workers over a long term of years, 

 following the orthodox methods of field trials, had produced very 

 meagre results and added little to the knowledge of the problems 

 involved. 



This led me to attempt to obtain some basic data by means of 

 sand cultures and in the initial stages I was particularly interested 

 in producing specimen plants deficient in each of the major plant 

 nutrients. These early results showed clearly that each deficiency 

 produced distinctive and characteristic visual effects, and later 

 work showed that these visual results could be usefully applied to 

 field problems of fruit crops. 



The experiments were subsequently extended to embrace a 

 wide variety of farm and market garden crops, and to include 

 problems relating to both major and trace elements. 



The particular aspects of plant nutrition which have received 

 attention in our experiments are as follows: 



1) The status of mineral nutrients in crop plants and the effects of 

 manures and fertilisers and of cultiual treatments on mineral nutrition. 



2) Pathological conditions resulting from defective mineral nutrition. 



3) The development of diagnostic and curative methods for use in the 

 field. 



During the course of our work it has been apparent that to 

 solve many of the problems which presented themselves it was de- 

 sirable to use a number of methods which could be used in compli- 

 mentary and confirmatory roles. These are as follows: visual di- 

 agnosis; foliage spraying and tissue injection with compounds of 



