Effects of Field Applications of Nitrate on Weed Seed Germination and Dormancy

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Abstract
Application of 112 to 336 kg/ha N as ammonium nitrate [NH4(NO−3)] failed to affect population numbers of common lambsquarters(Chenopodium albumL.), giant foxtail(Setaria faberiHerrm.), velvetleaf(Abutilon theophrastiMedic.), jimsonweed(Datura stramoniumL.), or redroot pigweed(Amaranthus retroflexusL.). Common lambsquarters seeds harvested from NO−3-treated plots were less dormant than control seeds. Seed germination in the laboratory increased from 3.0% for control seeds to 34.0% for seeds harvested from plots treated with 280 kg/ha N as NH4(NO−3). Nitrate concentration in common lambsquarters seeds increased as nitrogen fertilization increased. Seeds from nonfertilized plots contained 18.7 μg/g NO−3, while seeds from plots fertilized with 280 kg/ha N contained 126.3 μg/g. Adding exogenous NO−3to the germination medium brought the germination of most seed lots to a similar level, except for control seeds which germinated at a lower rate. In contrast to common lambsquarters, nitrogen fertilization did not greatly affect dormancy or NO−3accumulation in velvetleaf seeds. Exogenous NO−3failed to stimulate velvetleaf germination because dormant velvetleaf seeds did not imbibe.