Cover crop mixtures enhance stability but not productivity in a semi-arid climate

Authors: Franco, Jose; GRAMIG, GRETA - NORTH DAKOTA STATE UNIVERSITY; KENNETH, BEAMER - CALYXT; Hendrickson, John

Submitted to: Agronomy Journal
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 4/14/2021
Publication Date: 4/27/2021
Citation: Franco Jr, J.G., Gramig, G., Kenneth, B., Hendrickson, J.R. 2021. Cover crop mixtures enhance stability but not productivity in a semi-arid climate. Agronomy Journal. 113(3):2664-2680. https://doi.org/10.1002/agj2.20695.
DOI: https://doi.org/10.1002/agj2.20695

Interpretive Summary: Cover crop adoption often lags in semi-arid climates due to lack of timely rainfall and associated risks. Yet, they are being promoted as a way of enhancing ecological and agronomic services to make agriculture more sustainable in the long-term. A two-year study was conducted at two sites in North Dakota to evaluate the versatility of single species and multi-species cover crop plantings under ambient rainfall conditions and under irrigated conditions. The two sites differed in climates, dominant soil types, and management systems. We set out to identify whether mixtures are more versatile than single species plantings and to identify cover crop functional types that contribute consistently to overall production irrespective of differences in climates, soils, and management. Our results showed that multi-species mixtures do not necessarily produce more aboveground biomass than single species plantings, but they can produce with less variability when accounting for site differences, thus making them more versatile than single species cover crop plantings. Both warm and cool season grasses, foxtail millet and forage oat, contributed a large proportion of biomass production when planted in mixtures with leguminous and non-leguminous broadleaf cover crops. They also contribute with more consistency; more so than other functional types. Kale, a cool season non-leguminous broadleaf, increased in contribution to overall biomass production at both sites under ambient rainfall conditions in 2017 when less rainfall was received. This indicates that kale, along with warm and cool season grasses, could be an important crop to include in cover crop mixtures in semi-arid climates to reduce risks for producers. This information may help address some barriers to cover crop adoption in these moisture-limited environments and increase the sustainability of semi-arid cropping systems.

Technical Abstract: Cover crops are a critical component of sustainable agricultural systems, yet their performance in semiarid environments is often unreliable due to a lack of timely precipitation. In this manuscript we build upon previous research we conducted evaluating the performance of cover crop single and multi-species plantings with variable water input and compare their performance across two sites in North Dakota, USA. Three single species plantings including cowpea [Vigna unguiculata (L.) Walp.], Siberian foxtail millet [Setaria italica (L.) P. Beauv.] ,and sunflower (Helianthus annuus L.), and one 3-species (MIX3) and one 6-species (MIX6) mixtures were evaluated under ambient rainfall (dryland) and ambient rainfall with supplemental irrigation (dryland+) at one western (Mandan, ND, ‘West’) and one eastern site [Absaraka (2016) and Fargo (2017), ND, ‘East’]. No water regime treatment effect was detected for either site (West p = 0.2333, East p = 0.3910), but significant cover crop treatments were detected for both sites when averaged over years and water regime (p < 0.001 for both). Aboveground biomass production and water use efficiency (WUE) were not significantly greater from multi-species mixtures as compared to most single species plantings for both sites, and greater overall production and WUE were observed at the East site. At the West site, production variability was lowest with MIX6 when biomass was averaged over year and water regime (CV = 25%) compared to single species plantings (CV > 49%). At the East site, the single species cowpea planting had the lowest CV (24%) while MIX3 and MIX6 had CV values of 36 and 34%, respectively. However, across sites, MIX6 resulted in the least amount of variability (29%). Grasses generally contributed disproportionately to overall production and did so more consistently than other functional types at both sites. In 2017, when conditions were drier, kale’s [Brassica napus L. var. pabularia (DC.) Rchb.] contribution to overall productivity in the dryland treatment increased at both sites. Our results suggest mixtures may be more versatile across climates, soil types, and management systems and resilient cover crop mixtures should include warm and cool season grasses. Cover crop planting selections should take into account field soil variability and future unpredictable climate scenarios.