Establishment of alfalfa interseeded into corn in response to one cycle of selection and hybridization

Abstract

Intercropping alfalfa (Medicago sativa L.) in corn (Zea mays L.) can improve forage production, but wet growing conditions and high corn yields adversely impact alfalfa establishment. Therefore, we evaluated breeding alfalfa specifically for intercropping by selecting surviving plants from previous alfalfa varietal evaluations under corn and assigning them to five polycrosses to form cycle-1 synthetics. Pollen from four polycrosses was also used to generate hybrid seed using a male-sterility system. Corn was planted in May, intensively managed, and harvested for silage during September at Arlington and Prairie du Sac Wisconsin during 2019. Parental, polycross, and hybrid alfalfa entries were interseeded as swards between corn rows. Two subplots within each whole plot were treated with prohexadione, fungicide, and insecticide (PFI) or left as nontreated controls. Competition from high yielding corn combined with 43% above average precipitation during the growing season contributed to complete stand failure of nontreated alfalfa. Application of PFI improved foliar health, increased root mass, and enabled alfalfa establishment. Following corn silage harvest average stand density of PFI-treated polycross entries was 35% greater than parental entries (105 vs. 78 plants m −2 ); broad-sense heritability was 0.54. Overall, PFI-treated polycross and hybrid entries had similar stand densities after corn, but posthoc comparisons indicated two hybrids had twofold greater stand density than parental entries. These results indicate plant selection can be highly effective for developing polycross and hybrid germplasm with improved survival under corn. Our findings should stimulate further breeding work to improve alfalfa and other forages for use in intercropping systems.

Intercropping in maize silage versus solo‐seeding for alfalfa establishment in Wisconsin and Idaho

“…Application of PHD growth retardant and delayed interseeding usually reduced alfalfa plant height, but only the latter treatment was associated with improved yield of the maize silage companion crop, presumably because late seeding reduced the overall growth and early season competitiveness of alfalfa. By contrast, PHD treatment has little effect on leaf growth but reduces stem growth and enhances root growth in alfalfa (Grabber, Osterholz et al., 2021; Grabber, Riday et al., 2023) and these morphological shifts apparently had no impact on alfalfa's competitive effect on maize under the conditions of these studies.…”

“…Identical to system 1 but with prohexadione (PHD) growth retardant sprayed onto alfalfa to enhance seedling survival (Grabber, Smith et al., 2021; Grabber, Dias, & Renz, 2023).…”

“…The following cropping systems for alfalfa establishment were evaluated in both states: Maize silage interseeded early with alfalfa at maize planting. Identical to system 1 but with prohexadione (PHD) growth retardant sprayed onto alfalfa to enhance seedling survival (Grabber, Smith et al., 2021; Grabber, Dias, & Renz, 2023). Maize silage interseeded late with alfalfa at the vegetative emergence (VE) stage of maize. Identical to system 3 but with PHD sprayed onto alfalfa seedlings. Spring‐seeded alfalfa. Maize silage followed by spring‐seeded alfalfa in Year 2. Spring barley grown for grain and straw, followed by summer‐seeded alfalfa. Maize silage followed by late summer‐ or early fall‐seeded alfalfa. …”

Establishment of Alfalfa Intercropped under Corn in Response to Varying Rates of Prohexadione with or without Fungicide Plus Insecticide

“…Independent experiments were initiated in 2019 and 2020 at the Arlington Agricultural Research Station (43 • 18 N, 89 • 20 W) on a Plano silt loam (fine-silty, mixed, superactive, mesic Typic Argiudolls). The Arlington Station was chosen for this study because previous multilocation intercropping studies [8,17] indicated conditions at this location fostered relatively high levels of foliar damage and death of alfalfa seedlings under corn. Corn silage was grown prior to the 2019 study, and soybeans were grown prior to the 2020 study.…”

“…However, the clear benefits of fungicide and insecticide treatments on seedling health, vigor, and survival, especially under wet growing conditions, suggest that disease and perhaps insect pests play a large role in determining the success of alfalfa establishment under corn. Breeding new alfalfa varieties with greater survival under corn is one option for improving establishment in this system [17]. Further work to identify more effective agrichemical treatments and other improved management practices is also needed to ensure interseeding can be successfully realized under a wide range of production environments.…”