Influence of phosphorus and potassium on symbiotic nitrogen fixation
1944
Roberts, J.L. | Olson, F.R.
The nitrogen content of several experimental plots studied, on which a rotation including legumes was used, was higher where phosphatic and potassic fertilizers were applied than where no fertilizers were applied, in spite of greater removal of nitrogen by crops from fertilized plots. In some cases the nitrogen gain due to use of phosphorus and potassium was as much as 40 pounds of nitrogen per acre per year. The use of phosphorus and potassium on corn and wheat at Bedford, Indiana, caused an increase in the number of nodules and percentage nitrogen content of soybeans and lespedeza grown in subsequent years. In greenhouse experiments, fertilization of soybeans, alfalfa, and alsike clover increased nitrogen fixation by as much as 30% in some cases. Soybeans deficient in phosphorus are relatively lower in percentage nitrogen content and contain a somewhat higher concentration of soluble nitrogen than normal plants, suggesting that a deficiency of phosphorus may inhibit nitrogen fixation by interrupting protein synthesis. Soybeans deficient in potassium are relatively higher in percentage nitrogen and contain a lower concentration of soluble nitrogen than normal plants. These facts may be explained by assuming potassium to have some role in the synthesis or mobilization of carbohydrates.
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