A Study of the Effect of Potassium on the Yield, Duration of Stand and Chemical Composition of Alfafa

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Virginia Tech

The conclusion of the alfalfa fertility investigations at Glade Spring and at Culpeper may be summarized as follows;

  1. Potassium was the main limiting factor in the growth, duration of stand, vigor, and color of alfalfa.

  2. In general, yields were related directly to rate of potash fertilization.

  3. Yield variations due to phosphorus fertilization were insignificant.

  4. Sodium gave increased yields at Glade Spring and Location A at Culpeper, but had little or no effect on yields at Culpeper at Location B.

  5. In general, yields were decreased by the application of minor elements.

  6. In 1950 and 1951 at Glade Spring, more potassium was removed from the soil than was applied, the deficits ranging from only 8.4 pounds per acre of potassium where a 2-24-24 fertilizer was used, to 68.9 pounds per acre of potassium where e 2-12-0 fertilizer was used.

  7. The potassium removed per ton of hay was closely correlated with the rate of potassium fertilization.

  8. The phosphorus removed in the hay varied from 1/2 to 1/8 of the phosphorus applied in the fertilizer.

  9. The phosphorus removed was nearly constant regardless of the rates of phosphorus fertilization.

  10. Potassium decreased sodium uptake in the alfalfa; on the other hand, sodium had no effect on potassium uptake.

  11. Alfalfa appears to be a sodium accumulating plant when sodium is used as a supplement with potassium.

  12. Potassium depressed the absorption of calcium, magnesium, and sodium.

  13. At Glade Spring, potassium slightly depressed phosphorus absorption but had no noticeable effect on phosphorus uptake at Culpeper. Potassium appeared to have no appreciable effect on nitrogen content.

  14. The soil at Glade Spring had approximately 30 times as much exchangeable calcium as potassium. As a result, the calcium content of the alfalfa was often higher than the potassium content.

  15. Available phosphorus in the topsoil at Glade Spring was about five times higher than in the subsoil; on the other hand, available phosphorus at Culpeper was about equal in topsoil and subsoil.