Hybrid sudangrass and pearlmillet are noted as having a high potential for
accumulating nitrate (NO3) and poisoning cattle. Hay samples can be accurat
ely tested for NO3 content in the laboratory, however, this may take consid
erable time for farmers to obtain their results. This study was conducted t
o evaluate applicability of a quick Nitrate Meter for in-field testing of f
orage NO3 in the plant sap and to study the effects of nitrogen (N) fertili
zation on forage NO3 accumulation. Nitrate readings taken from the sap were
highly correlated with those using the conventional laboratory method (R-2
=0.85-0.95 for hybrid sudangrass and 0.91-0.94 for pearlmillet). Nitrate co
ncentrations varied with plant height, growing stages, locations in the tes
t plots, N rates and sources, and environmental conditions. Nitrate concent
rations in the whole plant decreased with plant height and plant maturity.
Higher NO3 levels were correlated with higher rates of N fertilizers. Nitra
te accumulation was also enhanced by drought stress. The quick NO3 test met
hod is easy to use and usually takes less than 20 minutes to obtain results
. This methodology allows increased management flexibility for farmers who
use warm-season annual grasses in their production systems.