Keith A. Kohler

Weed Seed Bank Dynamics During a Five-Year Crop Rotation1

Abstract: Cultural practices used for crop production influence the composition of the weed seed bank in the soil. This paper reports the results of a 5-yr experiment to characterize the weed seed bank conducted on a farmer-managed field in central Iowa. The number of weed seeds in the soil and their vertical distribution were examined each October. At the initial sampling in October 1994, the field had been in hay production and about 80% of the weed seeds were common waterhemp and foxtail species. The cropping sequence over the next 3 yr was corn/soybean/corn using a ridge tillage system. Over this period, the density of common waterhemp seeds declined each year. The density of foxtail seeds declined by almost 90% during the first year of corn and did not change during the following years of soybean and corn production. Prior to moldboard plowing of the hay sward in 1994, weed seeds were concentrated in the upper 10 cm of soil. Moldboard plowing resulted in a more uniform distribution of the weed seeds over the upper 20 cm of soil, and the distribution across depths remained relatively constant during the 3 yr of corn and soybean production. During the final year of the experiment, the field was rotated to oat and reseeded with hay species. The number of common waterhemp and foxtail seeds in the soil greatly increased following oat/hay production and seeds were concentrated in the upper 10 cm of the soil profile. Results indicated that the processes affecting the weed seed bank in production fields are complex and will vary greatly based on the production practices used and the timing of their application. Nomenclature: Common waterhemp, Amaranthus rudis Sauer #3 AMATA; corn, Zea mays L.; foxtail species, Setaria spp.; oat, Avena sativa L.; soybean, Glycine max (L.) Merr. Additional index words: Cropping systems, ridge tillage, seed bank, seed distribution.

Effects of Living Mulches on Predator Abundance and Sentinel Prey in a Corn–Soybean–Forage Rotation

Abstract Living mulches are cover crops grown concurrently within main crops for their benefits to weed control and soil quality. Because living mulches increase the diversity of vegetation in agricultural systems, they may impact the abundance or effectiveness of natural enemies. To examine the effects of living mulches on epigeal predators, arthropod abundance and feeding were examined in a rotation of corn (Zea mays L.), soybean (Glycine max L. Merr.), and forage crops in 2004 and 2005. Compared with a no-mulch control, the presence of alfalfa (Medicago sativa L.) and kura clover (Trifolium ambiguum M. Bieb.) mulches in corn and soybean increased predator abundance and consumption of European corn borer (Ostrinia nubilalis Hübner; Lepidoptera: Crambidae) pupae used as sentinel prey. A complementary effect of increased predation caused by corn and soybean was found when both annual crops with living mulches were compared with mulches grown alone. Positive correlations between the percentage of O. nubilalis pupae preyed on and ground beetle (Coleoptera: Carabidae) abundance suggest carabids contributed to the differences in predation. In 2005, fewer beetles correlated with consumption of O. nubilalis pupae [Poecilus chalcites (Say) and Scarites quadriceps Chaudior] were collected, and living mulch impacts on predation were less frequent. Both changes could be related to delayed herbicidal suppression of the living mulches in 2005, which seemed to homogenize predator community composition among the corn, soybean, and forage plots. Although living mulches alone may not provide sufficient pest suppression, their potential to enhance biological control should be considered along with their other agronomic benefits.

Rye Cover Crop Management Affects Grain Yield in a Soybean-Corn Rotation

Cover crops provide environmental benefits, yet their adoption into production agriculture has been limited. The objectives of this study were to determine how rye (Secale cereale L.) cover crop management affects yield of soybean [Glycine max (L.) Merr.] and corn (Zea mays L.) in a soybean-corn rotation. Field studies were conducted from 2001 to 2004 near Boone, IA. Prior to soybean, rye was controlled chemically and mechanically at Feeke’s growth stages 7 (2nd node visible), 9.8 (boot), and 10.5.1 (flowering). Prior to corn, reseeded rye from mechanical control plots was chemically controlled. In 2002 and 2003, no soybean yield differences were detected among timing treatments in mechanical control, which yielded 21 and 29 compared to 52 and 42 bu/acre in the no-rye check. In the chemical control treatments, soybean yielded 30, 39, 43, and 50 bu/acre in the 2nd node, boot, flowering, and check in 2002 and 29, 30, 36, and 43 bu/acre in 2003. Corn yield following rye was lower than the check in 2003 (133 versus 153). In 2004, corn yield only differed between the flowering treatment and the check. These results indicate that alternative rye cover crop systems must be developed to protect soil and water resources and provide economic returns.