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Potential Tetany Hazard of N-Fertilized Bromegrass as Indicated by Chemical Composition

Follett, R.F. and Power, J.F. and Grunes, D.L. and Hewes, D.A. and Mayland, H.F. (1975) Potential Tetany Hazard of N-Fertilized Bromegrass as Indicated by Chemical Composition. Agronomy Journal. 67:819-824.

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The objective of this field experiment was to determine
the effect of N fertilization on yield and chemical composition
of smooth bromegrass (Bromus inermis L.) and
the potential for grass tetany hazard in the northern
Great Plains as indicated by chemical composition of
bromegrass forage. Chemical components of forage considered
in relation to the hazard of tetany (a metabolic
disorder of ruminants resulting from forage with low Mg
availability) were inorganic cations, organic anions, aconitate,
and % total N/% total water-soluble carbohydrate
ratio (N/TWSC). Soil was Parshall fine sandy loam, a
pachic haploborall. Yields and chemical composition of
oven dried forage from plots not previously harvested
were determined at approximately 3-week intervals beginning
May 9. Differences between the sum (in meq/kg)
of inorganic cations (Na+, K+, Ca²+, Mg²+) and inorganic
anions (Cl-, No₃-, H₂PO₄-, SO₄²-) in forage was defined
as the concentration of organic anions (C-A).

Mature forage yield obtained from the unfertilized
check plot treatment on July 29 was only 29 and 22%
of yields obtained from plot treatments fertilized with 90
and 270 kg N/ha, respectively. The K/(Ca+Mg) ratios
and K concentrations increased during May and early
June, resulting in a K/(Ca+Mg) ratio near or above 2.2
during June and early June in oven dried forage from
fertilized treatments. Potassium, expressed as a fraction
K/C of the total cations (C), accounted for 35 to 74%
of the cationic charge. Fertilization with N increased total
N and K concentration and K/C in the forage. As K/C
increased, Mg/C and Ca/C decreased and K/(Ca+Mg) increased.
Aconitate and C-A concentration correlated
highly with K concentration and were increased by N
fertilization. Aconitate levels exceeded 1% on May 28;
the 270 kg N-treatment remained above 1% through July.
Nitrogen fertilizer increased N/TWSC in spring-harvested
forage, compared to unfertilized forage, and greatly accentuated
the peak N/TWSC values occurring in late
spring samples.

This study indicated that although potential for increased
forage and livestock-carrying capacity with N
fertilization is tremendous, N-fertilization may result in
a potential tetany hazard to ruminants. Therefore,
management practices are needed which minimize tetany
hazard while bromegrass yields are increased by N fertilization.

Item Type: Article
NWISRL Publication Number: 0337
Subjects: Irrigated crops > Grass forage > Chemistry
Soil > Amendments > Fertilizer
Mass Import - autoclassified (may be erroneous)
Depositing User: Dan Stieneke
Date Deposited: 20 Nov 2010 21:51
Last Modified: 15 Feb 2017 20:50
Item ID: 294