Aaron Daigh, Mary Savin, and Larry Purcell. Univ of Arkansas, 115 Plant Science Building, Fayetteville, AR 72701
A large portion of soybean, corn, and cotton acreage is planted as Round-Up Ready (RR) crops. Glyphosate (Round Up) is a post-emergence herbicide that kills a wide variety of weeds without damaging RR cultivars. Translocation of glyphosate from the aboveground plant to the root system may impact soil rhizosphere microorganisms. In a greenhouse study, effects of glyphosate on mycorrhizal infection and plant growth were tested in soybean, corn, and cotton. Low-P soil (11 mg P/kg) was compared with P-amended soil (45 kg P/ha added) for determining effects of P levels on infection. Additionally, soils were either not treated or treated with applications of glyphosate (1.1 kg/ha) at two and four weeks after planting. Plants were harvested six weeks after planting. Biomass and nutrient concentrations were measured and percent root infection was determined on cleared and stained roots. P fertilization increased shoot weight in corn, but not in soybean. On the other hand, P fertilization decreased root infection in soybean, but not corn. Glyphosate did not significantly affect plant shoot or root biomass or mycorrhizal root infection in corn or soybean. Reduced mycorrhizal infection may indicate the need for additional fertilizer supplements; whereas no significant effect in mycorrhizal infection may promote conservative fertilizer applications, potentially allowing economic savings for farmers. Further research is needed; however, these data suggest glyphosate may not interfere with plant biomass by altering mycorrhizal infection rates.