The benefits of intercropping in agricultural systems include the potential for better management of pests, pathogens, and weeds. Relay cropping (RC) consists of two or more crops grown in sequence with some overlap in the growth cycle, leading to sustainable intensification of the existing cropland. We hypothesized that the intercropping system affects crop productivity and the growth of weeds. We, therefore, evaluated the effects of crop diversity in relay cropping system on weed suppression compared with monocultures.
Field layout and evaluation
The field experiment was established in October 2023 at the Agricultural Engineering and Agronomy Research Farm near Boone, Iowa. Twelve 30 ft. wide × 30 ft. long plots with a 30 ft. alley between replications and 30 ft. borders were set up in a randomized complete block design. Four replicates for the three treatments included a control (no-till fallow/soybean monoculture), winter barley–soybean relay cropping (RC), and winter rye–soybean RC. The winter cereal rye (organic Hazlet) and winter barley (organic MN-Equinox) were drilled in 7.5-inch rows spacing. On May 17, 2024, untreated soybean variety P14A12E was drilled at 140k seed/Ac in a 30-inch row spacing using a 6-row John Deere 640 R planter.
Relay crop emergence, seedling diseases and weed infestation
Barley average emergence was significantly (P<0.05) lower (68.7%) compared with cereal rye (95%). Symptomatic seedlings with root/basal stem rot (Fig. 1) sampled from cereal rye and barley plots revealed the occurrence of four species of Alternaria, one each of Ascochyta, Bipolaris, Epicoccum, and Pyrenophora, five species of Fusarium, and three species of Pythium.
We identified 18 weed species (Fig. 2) — additional information on the weeds identified in this experiment is available at https://crops.extension.iastate.edu/encyclopedia/weed-identification-fact-sheets. The weed infestation in plots seeded with winter barley-soybean RC and cereal rye- soybean RC was significantly (P<0.05) lower compared with no-till fallow/soybean monoculture plots (Fig. 3) weed infestation and their identity and frequency recorded on June 10, 2024. In the no-till fallow/soybean monoculture plots, 90-95% of weeds represented were downy brome, little barley, yellow foxtail, woolly cupgrass, giant foxtail, and barnyardgrass (Fig. 2A), and 5-10% represent weeds depicted in Figs. 2B-2D. In barley-soybean RC and cereal rye-soybean RC plots, we observed yellow foxtail, giant foxtail, and common waterhemp (Fig. 2A) with very low to low infestations.
This research demonstrates the impressive weed suppression attainable with cropping systems incorporating winter annual cereal crops. Also, as the season progresses, we will evaluate for pests and diseases in no-till fallow/soybean monoculture, winter barley–soybean RC, and winter rye–soybean RC.
Acknowledgments
This project is supported by the Iowa Soybean Research Center (ISRC).
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- Field Agronomist in Central Iowa
- Associate Professor
- Extension Cropping Systems Specialist