Cellulosic crops are projected to provide a large fraction of transportation energy needs by mid-century. However, the anticipated land requirements are substantial, which creates a potential for environmental harm if trade-offs are not sufficiently well understood to create appropriately prescriptive policy. Recent empirical findings show that cellulosic bioenergy concerns related to climate mitigation, biodiversity, reactive nitrogen loss, and crop water use can be addressed with appropriate crop, placement, and management choices. In particular, growing native perennial species on marginal lands not currently farmed provides substantial potential for climate mitigation and other benefits.

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in yield over wider rows as reported by Porter et al. (1997). Nielsen (1988) reported a 2.7% increase in corn Continued genetic improvement in the ability of hybrid corn (Zea grain yield across nine Indiana locations when corn was mays L.) to withstand high plant density stress requires agronomists to periodically reassess optimal plant density and row width. Further-grown in narrow rows. The greatest advantage with narmore, the optimal plant density level and row width for corn grain row row systems seems to be in northern locations. yield may vary with location, primarily latitude, in the Corn Belt. This Paszkiewicz (1997) summarized 84 university and indusstudy was conducted to evaluate corn grain yield, harvest moisture, try studies and reported corn grown north of the Intertest weight, and stalk lodging with modern corn hybrids, as affected state 90 (I-90) corridor responded on average with an by row width and plant density in the northern Corn Belt. At six 8% increase in yield when row width was narrower than locations in 1998 and 1999, four hybrids differing in relative maturity, 76 cm. Furthermore, Cox et al. (1998) suggested that ear type, plant height, and leaf orientation were planted at row widths corn grown in narrow row widths north of 44Њ N had a of 76, 56, and 38 cm and five plant density levels ranging from 56 000 to 90 000 plants ha Ϫ1 . Plots were arranged randomly in a split-split yield advantage over wider rows. plot configuration. Results show that corn grain yield increased 2 andHybrids developed in recent years are able to with-4% and harvest moisture decreased by a factor of 2.1% when row stand higher plant density levels than older hybrids (Tolwidth was narrowed from 76 cm to 56 cm and 38 cm, respectively. lenaar, 1989). The current hybrids were found to have The highest plant density evaluated, 90 000 plants ha Ϫ1 , had the highest decreased lodging frequencies at the higher plant popugrain yield. Grain moisture decreased and grain test weight increases lations. Also, newer hybrids were able to better withslightly as plant density increased. A hybrid ϫ row width interaction stand environmental stress, resulting in production of was not observed indicating that hybrids that yield well in conventional fewer barren plants (Tollenaar, 1991). When selecting 76-cm row systems will also yield well in narrow row systems.Huron, Ingham, Kalamazoo, Monroe, and Saginaw counties. msu.edu).Abbreviations: GDU, growing degree units Published in Agron.

Hard-water cations, such as Ca+2and Mg+2, present in the spray solution can greatly reduce the efficacy of glyphosate. These cations potentially compete with the isopropylamine in the formulation for association with the glyphosate anion.14C-Glyphosate absorption by sunflower was reduced in the presence of Ca+2. The addition of ammonium sulfate overcame the observed decrease in14C-glyphosate absorption. Nuclear Magnetic Resonance (NMR) was used to study the chemical effects of calcium and calcium plus ammonium sulfate (AMS) on the glyphosate molecule. Data indicate an association of calcium with both the carboxyl and phosphonate groups on the glyphosate molecule. Initially, a random association of the compounds occurred; however, the reaction progressed to yield a more structured, chelate type complex over time. NH4+from AMS effectively competed with calcium for complexation sites on the glyphosate molecule. Data suggest that the observed calcium antagonism of glyphosate and AMS reversal of the antagonism are chemically based.