Phosphorus and nitrogen metabolism in soybeans as influenced by potassium

Abstract

The effect of K on P and N metabolism in soybean seedlings, Glycine max, Var. Dorman, was studied in two greenhouse experiments. Yield, nutrient uptake and changes in the distribution of cellular P and N compounds served as criteria for evaluating K effects. The yield increased exponentially with time regardless of K treatments; however, increasing K levels increased the rate of yield accumulation.

Phosphorus uptake was not associated with K levels. An increase in N uptake was associated with increased dry matter production rather than K levels, per se. An inverse relationship was found between per cent P and K levels. This was attributed to a dilution effect due to the increased yield with increasing K levels.

An extraction-time study on the lipid-free soybean leaf residue with 1N KOH, showed that essentially all of the extractable P and N was extracted within 45 and 60 minutes, respectively. Longer extraction times caused gradual protein hydrolysis.

Norit-A adsorbed P:N ratios were used to indirectly estimate the relative changes in poly-nucleotide-P (ATP and ADP) associated with K levels and ortho-P accumulation; indicating that K functions either directly or indirectly in the esterification of inorganic-P in coupled oxidative phosphorylation. From the data presented, it was concluded that under a general K stress, P metabolism exhibited a priority over N metabolism for K.

Based on these data, K was found to function in the following metabolic processes: (l) peptide-protein synthesis, (2) nucleic acid base synthesis, and (3) esterification of inorganic-P.