Phosphorus and Nitrogen relationships during spring growth of an aging timothy sward

0
Plant-based methods of determining P and N deficiencies require critical concentration values. We studied the response of timothy (Phleum pratense L.) to P and N fertilization over 7 yr with the objective of using relationships between P and N concentrations and dry matter (DM) yield to determine critical P and N concentrations. Timothy, seeded in 1998, was harvested during spring growth from 1999 to 2005 in an experiment with four sampling dates (stem elongation, early heading, late heading, and early flowering), four P applications (0, 15, 30, and 45 kg P ha–1), and four N applications (0, 60, 120, and 180 kg N ha–1). Maximum DM yield and, therefore, nonlimiting P and N conditions, were obtained with 120 kg N ha–1 without applied P. Under these nonlimiting conditions, relationships between P and N concentrations and DM yield changed with production years. Critical N concentration (Nc) in older swards (>4 yr; Nc = 37.0 x SB–0.35; R2 = 0.79), expressed as a function of shoot biomass (SB), was less than previous reports on younger swards (Nc = 48.0 x SB–0.32). Critical P concentration (Pc) was also less in older swards (Pc = 3.27 x SB–0.20; R2 = 0.68) than in younger ones (Pc = 5.23 x SB–0.40; R2 = 0.63). Critical P concentration can also be expressed as a function of N concentration (Pc = 1.07 + 0.063N; R2 = 0.71), a relationship independent of sward age and shoot biomass but affected by N deficiency; the slope is the same but intercept values vary from 1.31 to 1.41 when N limits shoot growth. Critical P and N concentrations can then be used to quantify the degree of P and N deficiency in young and old timothy swards.

Customer comments

No comments were found for Phosphorus and Nitrogen relationships during spring growth of an aging timothy sward. Be the first to comment!