LAND APPLICATION OF WASTE-WATER - EFFECT ON SOIL AND PLANT POTASSIUM

This study reports on the removal of potassium by a forage grass mixture from soil that received applications of waste water over a 5-year period. The forages, which received waste water at a rate of 5. 0 cm/week, were grown on either Windsor sandy loam or Charlton silt loam soil. the waste water annually suplied from 231 to 433 kg/ha of N and 36 to 153 kg/ha of K. The waste water contained more than twice as much N as K. Plant removal of K increased as the amount of N applied or removed by the forage increased. During the initial 4 years of the study, plant uptake of K exceeded the amount supplied by the waste water causing reduction in plant and soil concentrations of this element to low levels. Concentrations of K remained low in the soil solution throughout the study and tended to decline with time.; This study reports on the removal of potassium by a forage grass mixture from soil that received applications of waste water over a 5-year period. The forages, which received waste water at a rate of 5.0 cm/week, were grown on either Windsor sandy loam (typic Udipsamment) or Charlton silt loam (typic Dystrochrept) soil. The waste water annually supplied from 231 to 433 kg/ha of N and 36 to 153 kg/ha of K. The waste water contained more than twice as much N as K. Plant removal of K increased as the amount of N applied or removed by the forage increased. During the initial 4 years of the study, plant uptake of K exceeded the amount supplied by the waste water causing reduction in plant and soil concentrations of this element to low levels. Concentrations of K remained low in the soil solution throughout the study and tended to decline with time. The inadequate supply of K at this site was related to the low K/N ratio in the waste water applied. During the fifth year of study, K fertilization increased total plant yields and the concentration of this element in plants and soils to more nearly optimum levels. Since excessive K applications may also cause problems in plant or animal nutrition, total applications of K (waste water and fertilize) should be adjusted to be approximately 90% of the amount of N expected to be removed by the crop.