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|Title:||Aspects of Velvetleaf (Abutilon Theophrasti Medik.), Jimsonweed (Datura Stramonium L.) and Common Cocklebur (Xanthium Strumarium L.) Interference With Soybeans|
|Author(s):||Regnier, Emilie Elisabeth|
|Department / Program:||Agronomy|
|Degree Granting Institution:||University of Illinois at Urbana-Champaign|
|Abstract:||Velvetleaf (Abutilon theophrasti Medik.), jimsonweed (Datura stramonium L.) and cocklebur (Xanthium strumarium L.) are broadleaf weeds common in midwest soybean fields. Cocklebur causes greater yield reductions than velvetleaf and jimsonweed at equivalent densities. Cocklebur has a greater proportion of its leaves below the top of the soybean canopy where velvetleaf and jimsonweed have few to no leaves. Competititve effects of cocklebur may involve shading within the soybean canopy and space exclusion caused by its lower leaf canopy. Field and laboratory experiments were conducted to determine the causes for differences in leaf canopy of weeds below the top of the soybean canopy, to determine the importance of space exclusion and shading by weed leaves within the soybean canopy on soybean yield and other parameters, and to determine the cause for the apparent shade-tolerance exhibited by cocklebur.
Cocklebur had more leaves below the top of the soybean canopy than the other species because of greater branch number and longer branches, contributing to greater axillary leaf development. Lower branch initiation and growth were inhibited in jimsonweed and velvetleaf grown next to the soybean row.
Space exclusion combined with shading, simulated by cages covered with black plastic, caused increases in lodging, soybean height, height of bottom pod, and decreases in stem diameter, branches per plant, nodes per plant, pods per plant and soybean yield. Space exclusion without shading did not affect yield and affected fewer of the other parameters. Cocklebur utilized more space within the soybean canopy than did velvetleaf or jimsonweed due to its more developed leaf canopy. Shading within the soybean canopy may be a more important component in yield reductions caused by cocklebur than space exclusion.
Ribulose-1,5-bisphosphate carboxylase (rubisco) protein per unit leaf volume decreased in cocklebur in response to a decrease in growth irradiance but the content of this enzyme was unaffected by the decrease in irradiance level in jimsonweed and velvetleaf. Lower rubisco content implicates lower synthesis costs if turnover rates of rubisco are equivalent among species. If so, the resulting savings in energy and nitrogen may contribute to the shade-tolerance exhibited by cocklebur.
Thesis (Ph.D.)--University of Illinois at Urbana-Champaign, 1987.
|Date Available in IDEALS:||2014-12-16|