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Phosphorus and Nitrogen Relationships during Spring Growth of an Aging Timothy Sward
Author(s) -
Bélanger Gilles,
Ziadi Noura
Publication year - 2008
Publication title -
agronomy journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.752
H-Index - 131
eISSN - 1435-0645
pISSN - 0002-1962
DOI - 10.2134/agronj2008.0132
Subject(s) - dry matter , zoology , phosphorus , nitrogen , shoot , yield (engineering) , human fertilization , chemistry , biomass (ecology) , agronomy , biology , horticulture , materials science , organic chemistry , metallurgy
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 (N c ) in older swards (>4 yr; N c = 37.0 × SB −0.35 ; R 2 = 0.79), expressed as a function of shoot biomass (SB), was less than previous reports on younger swards (N c = 48.0 × SB −0.32 ). Critical P concentration (P c ) was also less in older swards (P c = 3.27 × SB −0.20 ; R 2 = 0.68) than in younger ones (P c = 5.23 × SB −0.40 ; R 2 = 0.63). Critical P concentration can also be expressed as a function of N concentration (P c = 1.07 + 0.063N; R 2 = 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.