Switchgrass (Panicum virgatum L.) is a valuable warm‐season native forage grass in Midwest grazing systems prompting interest in seed production to obtain adequate amounts of seed for planting purposes. Switchgrass seed production studies, however, have been primarily conducted in the Great Plains states. This study was conducted to evaluate cultivar response to row spacing and N fertilization for increasing seed yields in a more humid area of the species' natural adaptation. ‘Cave‐in‐Rock’ (C), ‘Blackwell’ (B), and ‘Pathfinder’ (P) switchgrass were established on a Webster loam (fine‐loamy, mixed, mesic Typic Haplaquoll) soil near Ames, IA, in 1978 in 20‐, 60‐, and 100‐cm rows and fertilized with N at 0, 90, and 180 kg ha−1 in 1979 and 1980. Seed yield and selected seed yield components were measured in 1979 and 1980. Seed yields averaged over 2 years, three N levels and three row spacings were 908, 319, and 388 kg ha−1 for C, B, and P, respectively. Greater lodging resistance, and greater seed yields in response to increased N level and decreased row spacing, contributed to the significantly greater seed yields of C. Seed yields of B and P were similar for all N and row‐spacing treatments. Cultivar rankings in percent fertile tillers varied between years. Inflorescences per unit area did not differ among cultivars, but total seed weight infloresence−1 averaged over years was 268 g for C, which was 54 and 40% greater than for B and P, respectively. Total seed weight inflorescence−1 seemed to be the most important seed yield component, followed by 100 seed weight for explaining seed yield differences among cultivars. Cave‐in‐Rock showed superior lodging resistance and a greater potential for increased seed production in narrow rows and at higher N levels in 2‐ and 3‐year‐old stands. Results showed that N management and row spacing of young stands of switchgrass grown for seed production in the humid Midwest varied according to the cultivar used. Cultivar susceptibility to lodging may be the most limiting factor to obtain high seed yields of some cultivars in the more humid areas of natural adaptation of switchgrass.

Eggshells are a byproduct from egg breaking facilities and potentially useful as an amendment for liming soils. Ground eggshells were evaluated as a liming material at two sites in Iowa with acidic surface soil. The study compared soil pH response and corn (Zea mays L.) and soybean [Glycine max (L.) Merr.] grain yield with multiple rates of agricultural lime (aglime) and ground eggshells (eggshells). Eggshells proved to be an effective liming material and land application for soil pH correction offers a practical use of eggshells. However, the reported effective calcium carbonate equivalent (ECCE) value for the ground eggshells was low as soil pH increase was greater than found with equivalent ECCE rates from aglime. Based on the soil pH responses in this study, it is suggested that ground eggshell ECCE values should be increased 2 to 3 times from reported values. That correction should help avoid over‐application and unintended high soil pH levels.

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