Interaction of Nitrogen, Phosphorus, and Potassium on Evapotranspiration Rate and Growth of Kentucky Bluegrass
- J. S. Ebdon ,
- A. M. Petrovic and
- R. A. White
Research is limited concerning the interactive effects of nitrogen, phosphorus, and potassium on turfgrass evapotranspiration (ET) rate. Previous research has emphasized the influence of N on growth and ET. In this study, a central composite experimental design was used to investigate the interactive effects of N, P, and K on Kentucky bluegrass (Poa pratensis L. ‘Majestic’) water use and growth under field conditions. Five treatment levels for each nutrient were used; N treatment levels ranged from 49 to 588 kg ha−1 yr−1, P from 0 to 86 kg ha−1 yr−1, and K from 0 to 348 kg ha−1 yr−1. Clipping yield and ET (measured in 25-cm diam. bucket-type lysimeters) were recorded on a weekly basis. A field study conducted in 1988 evaluated N, P, and K applied alone while in a 1989 field study N, P, and K combinations and interactions were evaluated. Applied alone, P and K had no effect on ET or shoot growth independent of the rate applied. Unless a high level of N was applied (588 kg ha−1 yr−1), N had no affect on shoot growth or ET. Shoot growth (clipping yield) and ET were highly correlated (r = 0.79, P ≤ 0.001) in the single nutrient study. There was an interaction between N, P, and K on shoot growth and ET. Shoot growth response was highly correlated with ET response when fertilized in the normal range of P for the soil type evaluated (0, 21.5, 43 kg P ha−1 yr−1). Evapotranspiration rate response to N, P, and K applied in combination were distinctly different from nutrients applied alone. At medium to high levels of N and P (294 kg N and 43 kg P ha−1 yr−1 and higher), water use increased in response to increasing K applied. Conversely, at N and P levels routinely applied to this species and soil type (147 kg N and 21.5 kg P ha−1 yr−1 and lower), increasing K levels minimized water use. Further research is needed to study specific interactions.Please view the pdf by using the Full Text (PDF) link under 'View' to the left.
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