Lecture 7 — 173 — Potassium Nutrition 



are often cited as evidence that potassium fertilization 

 is more effective in the years of unfavorable weather. 

 Some results from experiments conducted in the 

 controlled chambers at Berkeley suggested an inter- 

 reaction of light and potassium. But this view is not 

 necessarily supported by all available evidence. 



Relations of Nitrogen, Phosphorus and Potassium : — 



Much has been said about the balance of nitrogen, 

 potassium and phosphate in the nutrition of plants or 

 in the practical application of fertilizers to the soil. 

 With regard to this question, one needs to remember, 

 as one point, that a balance is not established in the 

 soil in direct accordance with the balance in the fer- 

 tilizer added. The chemical reactions of these three 

 nutrients with soil components are not alike. Potas- 

 sium and phosphate are fixed by soil colloids or other 

 components of the soil and by different reactions. 

 Nitrate is not fixed to an appreciable extent, although 

 ammonium may be temporarily. A soil balance of 

 nitrogen, phosphate and potassium, physiologically con- 

 sidered, must be based on the status of the soil as 

 affected by the chemical and biological reactions of 

 soil and fertilizer. It has already been noted that 

 potassium is fixed by soil components in several ways. 

 Moreover, within the plant itself the balance that 

 is determinative of plant growth is not confined to 

 the proportional relationships of inorganic nutrients. 

 The significant balance is rather governed by the inter- 

 reactions of inorganic nutrients with the carbon com- 

 pounds synthesized and metabolized. Potassium is one 

 of the elements required by the plant system as a 

 whole. It is self-evident that if nitrogen forms a 

 limiting factor for growth, an increased supply of 

 nitrogen will entail a greater demand for potassium 

 and vice versa. But the reduction of nitrate and the 

 metabolism of nitrogen compounds are also dependent 

 on available carbohydrate, and on all those phenomena 

 that are associated with organic catalysts, the enzy- 



