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Forages

Dietary Cation–Anion Difference of Timothy as Affected by Development Stage and Nitrogen and Phosphorus Fertilization

^a Dép. de Phytologie, Faculté des Sciences de l'Agriculture et de l'alimentation, Université Laval, Québec, QC, Canada G1K 7P4
^b Agric. and Agri-Food Canada, Soils and Crops Research and Development Centre, Québec, QC, Canada G1V 2J3

^* Corresponding author (belangergf{at}agr.gc.ca)

Received for publication August 4, 2005. Dry dairy cows (Bos taurus) fed forages with a high dietary cation–anion difference (DCAD) are more likely to develop hypocalcaemia. We determined how development stage at harvest and N and P fertilization can be used to reduce the DCAD to <250 mmol_c kg^–1 dry matter (DM) for timothy (Phleum pratense L.) grown on a soil high in K content. Stages of development (stem elongation, early heading, late heading, and early flowering) in spring growth, and treatments of P (0, 15, 30, and 45 kg ha^–1) and N (0, 60, 120, and 180 kg ha^–1) fertilization were evaluated. Concentrations of K, Na, Ca, Mg, Cl, S, and P of timothy were determined and the DCAD was calculated with a short (DCAD_S) and a long (DCAD_L) equation. From stem elongation to early flowering, DCAD_S decreased from 326 to 196 mmol_c kg^–1 DM and DCAD_L from 297 to 181 mmol_c kg^–1 DM; this reduction was attributed to a decrease in K concentration and a slight increase in Cl concentration with development stage. Nitrogen fertilization increased DCAD_S and DCAD_L only at stem elongation; the lack of a response at later stages of development is explained by the concomitant increase in both K and Cl concentrations with increasing N fertilization. Phosphorus fertilization did not affect DCAD_S and DCAD_L even though it increased timothy P concentration. Harvesting timothy at late heading, with an appropriate N fertilization to ensure adequate yield, is an option to produce a forage with a DCAD of <250 mmol_c kg^–1 DM on a soil high in K.

Abbreviations: DCAD, dietary cation–anion difference • DCAD_L, DCAD calculated using a long equation • DCAD_S, DCAD calculated using a short equation • DM, dry matter • PCA, principal component analysis • SEM, standard error of the mean

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