Oat companion seeding rate, herbicide, and irrigation effects on alfalfa stand establishment

Authors: ROBERTS, CARSON - UTAH STATE UNIVERSITY; Robins, Joseph; YOST, MATT - UTAH STATE UNIVERSITY; RANSOM, C - UTAH STATE UNIVERSITY; CREECH, EARL - UTAH STATE UNIVERSITY

Submitted to: Agronomy Journal
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 9/21/2022
Publication Date: 10/12/2022
Citation: Roberts, C., Robins, J.G., Yost, M.A., Ransom, C., Creech, E.J. 2022. Oat companion seeding rate, herbicide, and irrigation effects on alfalfa stand establishment. Agronomy Journal. 115(1):273-285. https://doi.org/10.1002/agj2.21227.
DOI: https://doi.org/10.1002/agj2.21227

Interpretive Summary: Alfalfa is frequently seeded with an oat companion crop to suppress weeds and provide more rapid forage production during establishment. Unfortunately, seeding rate recommendations do not exist for these mixtures for limited irrigation and dryland production settings. Alfalfa-oat mixtures from 0 to 79 pounds of oat per acre seeding rates were evaluated under five irrigation levels. Alfalfa establishment was best with no or limited oat. However, weeds also increased with lower oat rates. Stem density was substantially higher with the increased oat seeding rate, particularly at the lower irrigation levels. First harvest forage yield was highest with greater oat seeding rate and differences among seeding rates increased with decreasing irrigation. In contrast, second harvest forage yields were highest at lower oat seeding rates. The herbicide, no oat, treatment produced the forage with the highest quality. Alfalfa-oat seed mixtures must be appropriately paired with available irrigation to ensure alfalfa establishment, weed suppression, and initial forage production without suppressing future forage production. The best approach is a low to moderate oat seeding rate, or the use of herbicide.

Technical Abstract: Alfalfa (Medicago sativa L.) -oat (Avena sativa L.) companion crop seeding rate recommendations vary, and no recommendations exist for alfalfa-oat companion establishment in reduced moisture conditions. This study was conducted to offer updated information on optimal oat companion seeding rates for alfalfa establishment, depending on moisture availability. In this study, the effects of 0 (untreated and with herbicide), 11, 22, 45, and 89 kg ha-1 oat companion seeding rates were evaluated under 5 irrigation levels (ILs) at North Logan, UT on a Millville silt loam (coarse-silty, carbonatic, mesic Typic Haploxeroll). At the two highest ILs in first cut, a small, 2-fold increase in stem density occurred as the 89 kg ha-1 oat rate was reduced to 11 kg ha-1, but at the lowest two ILs, the increase was 5 -7 -fold. Similarly, second cut differences in stem density were only apparent at lower ILs. First cut forage yields were lowest in 0 kg ha-1 treatments and increased with increasing oat seeding rates. These differences in yield were amplified as ILs were reduced. Conversely, yields were highest among 0 kg ha-1 treatments at second cut. Control of weeds were similar to herbicide at the highest oat seeding rates. Generally, the presence of oats or weeds reduced quality, with herbicide, untreated, and 11 kg ha-1 treatments resulting in first cut crude protein levels of 18, 14, and 10% -respectively. Alfalfa establishment is most favorable when oat seeding rates are reduced as moisture is reduced.