Grass tetany, a Mg deficiency in ruminants, is responsible
for large economic losses throughout temperate regions.
Significant livestock losses occur in the semiarid
western United States primarily when livestock are grazing
the spring growth of Agropyron desertorum, an introduced
grass species which provides much needed early
spring forage.
The objective of this study was to increase forage Mg
to about 0.2% by Mg and N fertilization and thus meet
animal needs and reduce losses from death. The field
study was located on A. desertorum grassland which had
previously produced grass tetany. Two calcareous aridisols
were each fertilized with 0, 90, 200, and 600 kg Mg/
ha as MgSO?•7H?O, having split plots with 0 and 150
kg N/ha applied as NH?NO?. Forage was harvested at
regular periods intended to bracket the spring occurrence
of tetany for three seasons following fertilization.
Fertilization with 600 kg Mg/ha was necessary to increase
forage Mg to the recommended level (0.2%). Applying
150 kg N/ha increased forage Mg concentration
as much as did 200 kg Mg/ha. The N and Mg fertilizers
were additive in increasing forage Mg concentrations.
Forage Mg concentrations decreased with increasing age
of vegetatively growing grass, and the benefits from fertilization
were less with each successive season following
fertilization. Little residual effect of 600 kg Mg/ha or 150
kg N/ha fertilization on plant Mg concentration would be
expected after 5 years. Rapid decreases in water-soluble
soil Mg with the resulting formation of some unknown
insoluble phase, as well as high investment costs, preclude
Mg fertilization of these ranges to meet Mg requirements
of grazing animals
