Assessment of Foliar and Fertilizer Impregnated Mo for Effect on Nitrate Concentration in Johnsongrass
Applied Research
Brian Haller
CEA-STAFF CHAIR
University of Arkansas Cooperative Extension Service
SEARCY
Abstract
Toxic nitrate accumulation is a recurring problem in summer forages including sorghum-sudangrass (Sorghum bicolor L. Moench X Sorghum sudanese P. Stapf) and johnsongrass (Sorghum halepense L. Pers.) during drought periods in summer. The earliest authentic accounts of nitrate toxicity were reported by Mayo in 1895 when cattle died after eating cornstalks (Wright and Davidson, 1964). Acute nitrate poisoning causes anoxia in animals resulting in abortion of fetuses, low productivity, or death (Garner et al., 1979). Nitrate toxicity occurs most often during periods of drought, combined with nutrient deficiency, cloudy weather, or when heavy N applications have been made. However, toxic levels can occur under high N fertilizer application even with good rainfall. Although numerous studies have been done to determine the mechanism of toxic nitrate accumulation, no good recommendation exists for reducing these toxic levels in forage so that they can safely be used for livestock feed. Micronutrients play a major role in nitrate reductase (NR) activity. Molybdenum deficiency can lead to high nitrate levels since Mo is required by NR (Marschner, 1986). Graham (in Davies, 1956) described soils of known and suspected Mo deficiency as being highly weathered with a high percentage of quartz and extremely low amounts of feldspars. This description fits many Arkansas soils and a large part of the southeastern United States. Ramani and Kannan (1986) reported higher NR activity in sorghum supplied with increasing amounts of Mo. Forage nitrate-N concentrations below 700 ppm are considered safe for livestock consumption with no additional feeding modifications. If Mo seed treatment or foliar Mo application can reduce toxic forage nitrate concentrations to safe levels for livestock use, producers throughout the U.S. could benefit. Fewer animals would be lost from nitrate poisoning. Application of Mo as foliar applied or impregnated fertilizer did not reduce incidence or concentration of high nitrate-N levels in post-application samples of johnsongrass forage. Forage nitrate concentration was not as high as expected at the highest N rate application of nitrogen fertilizer at 150 lbs/a increased nitrate-nitrogen concentrations above safe levels (700ppm).
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Authors: Brian Haller, Danny Griffin
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Haller, B. CEA-STAFF CHAIR, University of Arkansas Div. of Agriculture Cooperative Extension Service, Arkansas, 72143
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Griffin, D. County Extension Agent - Staff Chair, University of Arkansas Div. of Agriculture Cooperative Extension Service, Arkansas, 72031