Cover crops and their role as an integral nitrogen management strategy for sandy soils

June 28, 2024

by Eduardo Garay Lagos, Doctoral student, Department of Soil, Water and Climate

The State of Minnesota has approximately 600,000 acres of irrigated sandy soils which are predominantly under corn and soybean cultivation. These soils are highly important for the State’s economy and for the global supply of the “4Fs” – food, fiber, fuel, and feed. However, challenges arise as naturally these soils have a low water holding capacity and an equally high nitrate leaching potential. If not managed properly, there is a latent risk of increasing the environmental impact footprint that can have greater repercussions affecting stakeholders locally and globally. For instance, nitrate leaching could lead to the contamination of groundwater sources or cause the eutrophication of water bodies which exacerbate the negative impacts from climate change.

Nitrogen is generally one of the most critical nutrients when designing plant nutrition programs given the high demand from the plant relative to other nutrients. Nevertheless, nitrogen is highly dynamic and often challenging to manage given current highly variable and unpredictable weather conditions. Thus, implementing the use of cover crops can offer an alternative practice that provides multiple agroecosystem services benefitting crop productivity and minimizing the environmental impact. To successfully integrate this practice, we first need to fully understand the effect that cover crops have on both the N dynamics and the competition with other crops for resources.

Kura integrated in corn plots
Kura clover growing in between the corn plots as a living mulch system throughout the growing season. The white containers observed right above the Kura canopy are acid traps utilized to monitor ammonia volatilization.

That is why this study aims to holistically evaluate and compare the impact of annual vs. perennial cover crop systems and their interaction with different nitrogen rates on irrigated sandy soils. We used rye for the annual, and Kura clover for the perennial systems respectively, while also comparing it to a baseline system with no cover crop. In addition, we are also evaluating three different crop rotations including continuous corn, corn after soybean, and soybean after corn to provide a diverse and comprehensive set of row crop production scenarios. Throughout the growing season, we evaluated a myriad of variables which will allow us to quantify both the agronomical and environmental tradeoffs that each system offer. More importantly, the study offers the novelty of including one of the most holistic N dynamics assessments within these type of production systems at a field scale. This is achieved through monitoring the mineralization, organic accumulation, crop utilization, nitrous oxide emissions, ammonia volatilization, and nitrate leaching.

So far, we have found some fascinating insights which indicate that cover crops can be successfully adapted and create incredible opportunities for growers. For instance, Kura Clover used as a living mulch has the potential to reduce nitrate leaching up to a 60% across all the crop rotations when compared to the rye and no cover systems. This nitrogen retained within our production system represent both dollar savings in terms of fertilizer that does not go “down the drain” while also preventing an environmental contamination hotspot. Certain yield penalty can occur given the aggressive competition from having another crop growing between the rows particularly on dry years. However, this is something that can be mitigated with proper irrigation management. Also, other preliminary results indicate a potential of Kura clover to reduce nitrous oxide emissions, a potent green house gas with the potential of warming up the earth 300 times more than carbon dioxide.

This project is part of a longer-term effort that started over a decade were a wider range of research outputs have been produced on multiple nutrient management aspects. Our latest efforts are focused in expanding the toolkit that our farmers have particularly when dealing with a global market that continuously demands an environmentally sound increase in productivity. This study will allow us to generate one of the most comprehensive nitrogen budgets which will better inform the cost-benefit relationship of implementing cover crops in these systems. Consequently, we will be able to recommend adjustments in nitrogen management practices that integrate a holistic lens towards maximizing stakeholder value and responsible environmental stewardship.

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