Lecture 7 — 151 — Potassium Nutrition 



the prune trees were planted were rated as of excellent 

 character agriculturally. Nevertheless, preliminary 

 study of the soils led to the belief that they might be 

 lacking in power to supply potassium to the trees at 

 an adequate rate. The first chemical examinations of 

 samples of soil from some badly affected areas showed 

 in particular very low concentrations of soil solution 

 potassium and also low amounts of potassium that 

 could be released in the base exchange process, which 

 has been given some attention in an earlier lecture. 

 These data were not in themselves conclusive of a pot- 

 assium deficiency, as we shall later show, but they gave 

 reason for an investigation of this possibility. (See 

 plates 27 and 28) . 



In the subsequent years, the investigation expanded 

 into a diversified study of the potassium nutrition of 

 plants in relation to soil problems, which embraced 

 laboratoiy, greenhouse, and field experimentation*. It 

 happened also that in this period there was a re- 

 crudescence of interest by various investigators in 

 the status of soil potassium, in part based on the de- 

 velopment of knowledge of the crystal structure of 

 soil colloids. The results of general research on potas- 

 sium now available present, therefore, an opportunity 

 to illustrate the nature of an attack on a problem of 

 the system, soil-plant-atmosphere. The immensity of 

 the literature dealing with potassium and plant growth 

 of necessity limits this discussion to several of the 

 broader aspects of the subject. 



The thought might occur at first to many persons 

 that if a deficiency of potassium were an important 



*For many years Dr. O. Lilleland has conducted field 

 experiments with trees, accompanied by laboratory studies, 

 and various other members of the Experiment Station have 

 made researches on the general aspects of potassium nutrition 

 of plants. In one experiment, large lots of soil were trans- 

 ported to Berkeley and placed in cylinders holding 1000 pounds 

 of soil. Prune trees were grown under these conditions for 

 about seven years and chemical examinations were made on 

 the soils and tissues of the trees. 



