It is known that glyphosate is toxic to the bacteria, which forms nodules and fixes nitrogen in soybeans, when the bacteria is grown in direct contact with glyphosate in petri dishes. However, does glyphosate affect the bacteria in the roots of Roundup Ready (RR) soybeans? Researchers in Arkansas (King and others) tested this question by spraying inoculated RR soybeans in nitrogen-free soil in the greenhouse. When the RR soybean seedlings were sprayed twice with 1.5 qt/a of Roundup Ultra (at 5 days after emergence and again at 10 days after emergence), there was a reduction in the weight of the nodules and a slight reduction in the shoot weight at 9 days after the second glyphosate application. However, by 30 days after the second glyphosate application, the soybeans recovered. The shoot weights, nodule weights, and nitrogen concentration in the soybeans were the same if sprayed with glyphosate or not. They also sprayed larger soybeans three times with 1.5 qt/a of Roundup Ultra (at 18, 25, and 32 days after emergence). This was a total of 4.5 qt/a of Roundup Ultra. When measured 8 days after the last glyphosate application, these soybeans had the same shoot weights, nodule weights and nitrogen concentration as soybeans that were not sprayed.
Nitrogen, Glyphosate & Chlorophyll
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