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Higher Fatty Acid Content of Perennial Grasses as Affected by Species and by Nitrogen and Potassium Fertilization¹

Levels of higher chain fatty acids (HFA) in grass herbage may be an important factor in incidence of hypomagnesaemia. The objectives of this study were to determine HFA content of six cool season grasses³ and to investigate the effect of N and K fertilization on HFA content of grasses.

HFA content was determined for Bromus inermis L., Dactylis glomerata L., Festuca arundinacea Shreb., Poa pratensis L., Phleum pratense L. and Phalaris arundinacea L. The range in mean HFA among species was small 03.0 to 14.8 meq/100 g dry wt.). Only Kentucky bluegrass had significantly lower HFA than the mean of all species. Its mean N concentration was also the lowest.

Mean HFA content increased 25% in orchardgrass and 46% in bromegrass with 112 kg/ha N fertilization. Potassium fertilization up to 403 kg/ha had no effect on HFA content.

High correlations (r .89, significant at the 1% level) were found between HFA and N concentration for the six species and for bromegrass and orchardgrass in the N fertility experiment. Regression coefficients for predicting HFA concentration from herbage N concentration compared closely to the regression coefficient determined on mixed herbages in New Zealand.

Nitrogen source (NO₃-N vs NH₄-N) did not differentially influence HFA content of perennial ryegrass (Lolium perenne L.) grown in nutrient culture when 28 to 56 mg N/liter of solution were used. Low NO₃-N (1.6 mg N/ liter) shoots had a greatly reduced HFA and N concentration. Level of HFA in ryegrass roots was not significantly influenced by either N rate or form, although N in roots varied from 1.35% to over 5%. This contrast between roots and tops implies that the concentration of N per se in a tissue does not always determine HFA accumulation. The data support the hypothesis that the relationship between N and HFA concentration in grasses may be mediated by photosynthesis.

Key Words: Grass tetany • Hypomagnesaemia • Mg availability • Nitrate • Ammonium • Bromus inermis L. • Dactylis glomerata L. • Festuca arundinacea Shreb. • Poa pratensis L. • Phleum pratense L. • and Phalaris arundinacea L.

² Assistant professor of agronomy, Ohio Agr. Res. and Dev. Cen., Wooster, OH 44691.

Received for publication April 22, 1974.

This article has been cited by other articles:

				I. M. Witkowska, C. Wever, G. Gort, and A. Elgersma Effects of Nitrogen Rate and Regrowth Interval on Perennial Ryegrass Fatty Acid Content during the Growing Season Agron. J., August 11, 2008; 100(5): 1371 - 1379. [Abstract] [Full Text] [PDF]