Potential tetany hazard of N-fertilized bromegrass as indicated by chemical composition

Follett, R.F.; Power, J.F.; Grunes, D.L.; Hewes, D.A.; Mayland, H.F.

Agronomy Journal 67(6): 810-824


ISSN/ISBN: 0002-1962
DOI: 10.2134/agronj1975.00021962006700060024x
Accession: 000464393

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In trials in 1968, herbage yield of brome grass cv. Lincoln given 0, 90 or 270 kg N/ha and 28 kg P/ha on 2 May and sampled at 3-weekly intervals from 9 May to 1 Oct. was significantly increased by 90 kg N from 18 May and by 270 kg N from 29 July onwards with highest yield of 1.7, 5.7 and 7.4 t/ha, respectively, on 29 July. Herbage K content and K:Ca + Mg ratio increased during May and early June with the ratio in stands given N more than or equal to 2.2 during June and early July. K expressed as a fraction of total inorganic cations (C) accounted for 35-74% of the cationic charge. Applied N increased herbage N and K content and K:C, K:Ca + Mg and N:total water-soluble carbohydrate ratios and decreased Mg:C and Ca:C ratios. Hypothetical blood serum Mg values were 13 and 18 ppm with 90 kg N and 16 and 14 ppm with 270 kg N/ha at the 28 May and 18 June harvests, respectively, and >20 ppm with all other harvests and treatments. It was concluded that the markedly higher yields obtained with applied N might be associated with a tetany hazard in the absence of suitable management practices.