Few experiments have studied how seeding rates affect agronomic performance and end‐use quality of modern wheat (Triticum aestivum L.) genotypes in the Great Plains. Higher grain yield and better quality grain production requires the use of appropriate seeding rates. During the 1997 and 1998 crop seasons, 20 winter wheat genotypes and experimental lines were evaluated at two locations (four environments) to assess seeding rate and genotype effects on agronomic performance and end‐use quality of wheat. Significant differences among environments, seeding rates, and genotypes, and some of their interactions were identified. Lower seeding rates decreased plant population (by 62.3%), grain yield (by 0.8 Mg ha−1), kernel weight (by 1.3 mg kernel−1), flour yield (by 0.8 g/100 g grain), mixing time (by 0.7 min), caused later flowering (by 2 d), and increased flour protein content (by 15 mg g−1) and mixing tolerance (1 unit). Environment × genotype interactions were significant for all the traits except plant population and mixing tolerance. On the basis of the four environments, the seeding rate × genotype interactions were nonsignificant for all traits except plant height. These results provide evidence that agronomic performance and end‐use quality traits are greatly influenced by the environmental conditions and less so by seeding rates. Seeding rate affected plant population, days to flowering, plant height, grain yield, kernel weight, flour yield, flour protein, and mixing time and tolerance of wheat; therefore, seeding rate should be considered as a factor in obtaining higher grain yields with good end‐use quality.

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Herbicide‐resistant crops like glyphosate resistant (GR) soybean [Glycine max (L.) Merr.] are gaining acceptance in U.S. cropping systems. Comparisons from cultivar performance trials suggest a yield suppression may exist with GR soybean. Yield suppressions may result from either cultivar genetic differentials, the GR gene/gene insertion process, or glyphosate. Grain yield of GR is probably not affected by glyphosate. Yield suppression due to the GR gene or its insertion process (GR effect) has not been reported. We conducted a field experiment at four Nebraska locations in 2 yr to evaluate the GR effect on soybean yield. Five backcross‐derived pairs of GR and non‐GR soybean sister lines were compared along with three high‐yield, nonherbicide‐resistant cultivars and five other herbicide‐resistant cultivars. Glyphosate resistant sister lines yielded 5% (200 kg ha−1) less than the non‐GR sisters (GR effect). Seed weight of the non‐GR sisters was greater than that of the GR sisters (in 1999) and the non‐GR sister lines were 20 mm shorter than the GR sisters. Other variables monitored were similar between the two cultivar groups. The high‐yield, nonherbicide‐resistant cultivars included for comparison yielded 5% more than the non‐GR sisters and 10% more than the GR sisters.

The seed composition in the upper 15-cm soil horizon was determined and correlated with weed seedlings growing with fieldbeans (Phaseolus vulgarisL. ‘Valley’). The total seed reservoir averaged 250 seed/kg of soil, and 19 species were represented. Seed occurring with the most frequency were redroot pigweed (Amaranthus retroflexusL. ♯ AMARE), common lambsquarters (Chenopodium albumL. ♯ CHEAL), and common purslane (Portulaca oleraceaL. ♯ POROL). Seed from these plants accounted for over 85% of the seed found. The number of barnyardgrass [Echinochloa crus-galli(L.) Beauv. ♯ECHCG], buffalobur (Solanum rostratumDunal ♯ SOLCU), common lambsquarters, common purslane, and common sunflower (Helianthus annuusL. ♯ HELAN) seed in the soil was correlated with the number of plants growing in the field with fieldbeans. A correlation occurred between redroot pigweed, yellow foxtail [Setaria lutescens(Weigel.) Hubb. ♯ SETLU], and barnyardgrass growing in corn (Zea maysL.) fields in the fall of the year and plants growing in the field with fieldbeans the following year.

Glyphosate (N-(phosphonomethyl) glycine)-resistant (GR) soy- Missouri, personal communication, 1999). bean [Glycine max (L.) Merr.] technology is gaining acceptance in U.S. cropping systems, yet potential yield suppression from eitherYield suppression may result from either (i) cultivar cultivar genetic differentials, the GR gene/gene insertion process, or genetic differentials, (ii) the GR gene/gene insertion glyphosate is a concern. Other work shows that the GR gene/gene process (GR effect), or (iii) glyphosate (herbicide efinsertion process may suppress soybean yield. No one has reported fect), or a combination of the three. Thus, in the first the effects of glyphosate on a diverse group of commercially available situation yield of GR cultivars may be suppressed rela-GR soybean cultivars. In this study we evaluated one of the potential tive to that of other cultivars simply because the GR sources of GR yield suppression-the effect of glyphosate on yield, gene was inserted in low yielding or older cultivars. We growth, and development of GR cultivars. Field experiments were consider yield suppression associated with the GR effect conducted at four Nebraska locations with12 GR cultivars in 1998 and or herbicide effect a greater potential problem than 13 GR cultivars in 1999. Soybean response to glyphosate, ammonium cultivar genetic differentials since the latter can be oversulfate (AMS), and water application at 21 and 42 d after soybean emergence was compared with control plots treated with AMS and come by inserting the GR gene in high yielding parent water in 1998. An additional control, water alone, was added in 1999.