Summary• Senna obtusifolia (sicklepod) is a troublesome weed in many agronomic cropping systems in the southeastern USA with varying fertility regimes. This series of experiments was initiated to determine the impact of nutrient availability on reproductive output and maternal effects.• Experiments were conducted with plants growing in soil in growth chambers for 120 d. Offspring growth was evaluated in hydroponics.• Plants grown under higher nutrient conditions had greater reproductive biomass, number of seeds and total seed biomass. Individual seed mass distributions were slightly affected, with negative skewness decreased at higher nutrition. Seed germination rates were influenced primarily by seed size, as small seeds germinated faster than large seeds. The nitrogen content of seeds increased with increasing seed size and was higher in the high nutrition treatment. Seedlings arising from maternal plants grown under high nutrition grew more rapidly than did seedlings arising from maternal plants grown in a low nutrient regime.• The results suggest that S. obtusifolia reproduction and offspring competitiveness can be strongly influenced by the fertilization regimes used in different agronomic crops and rotations.

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The low-nitrogen status of highly weathered soils may offer a potential alternative for weed suppression in agricultural systems with N2-fixing crops. In this study, we used sicklepod as a model to evaluate weed response that might occur with managed reductions in nitrogen-soil fertility. A field study was conducted with the parental generation supplied 0, 112, 224, or 448 kg N ha−1. Decreased nitrogen fertility led to reduced shoot biomass, seed number, and total seed mass. Individual seed mass was lower, but seed % nitrogen was not affected. Analysis of seed-mass distribution confirmed that low parental fertility was associated with more small seeds as a proportion of total seeds produced. Additional experiments in hydroponics culture revealed slower growth rates of seedlings produced from small seeds when grown under low-nitrogen conditions. Competitiveness of plants from small (low nitrogen) and large (high nitrogen) seed classes was determined in a replacement-series experiment conducted in sand culture in a controlled environment at two densities and two levels of nitrogen nutrition. Plants produced from smaller seeds were less competitive in low-nitrogen fertility conditions, but plants from small and large seeds competed similarly when grown under high-nitrogen fertility. The results support the hypothesis that comprehensive management strategies to reduce nitrogen availability for weed growth in low-fertility conditions could decrease weed interference by decreasing growth and seed production of parental plants and through maternal effects that lower competitiveness of offspring.