Rotational complexity increases cropping system output

A summary of the paper published in One Earth, Volume 7, Issue 9, 20 September 2024, Pages 1638-1654 – https://doi.org/10.1016/j.oneear.2024.07.008

Agriculture faces increasing challenges from unpredictable weather. Diversifying crops over space and time can help maintain productivity and enhance the resilience of agroecosystems by enabling farmers to adapt to environmental risks. We quantified crop output under different rotations using 20 long-term datasets. By examining crops and complete rotations, we quantified the portfolio effect under various growing conditions. Assessing outcomes using multiple metrics, soil types, and cropping systems reduces uncertainty about adopting more diverse rotations, crucial under increasing production risks from adverse weather. This will inform stakeholders—from farmers to policymakers to lenders—in supporting cropping systems, policies, or programs that reduce risk. Moving forward, our efforts can enhance our understanding of the value of diverse crop rotations and insights connecting agricultural practices to societal outcomes from farm economic performance to consumer nutritional choices.

Summary

Growing multiple crops in rotation can increase the sustainability of agricultural systems and reduce risks from increasingly adverse weather. However, widespread adoption of diverse rotations is limited by economic uncertainty, lack of incentives, and limited information about long-term outcomes. Here, we combined 36,000 yield observations from 20 North American long-term cropping experiments (434 site-years) to assess how greater crop diversity impacts productivity of complete rotations and their component crops under varying growing conditions. Maize and soybean output increased as the number of species and rotation length increased, while results for complete rotations varied by site depending on which crops were present. Diverse rotations reduced rotation-level output at eight sites due to the addition of lower-output crops such as small grains, illustrating trade-offs. Diverse rotations positively impacted rotation-level output under poor growing conditions, which illustrates how diverse cropping systems can reduce the risk of crop loss in a changing climate.

Introduction

Crop diversification through rotations is a key strategy to improve agroecosystem resilience under climate uncertainty. Diverse rotations, incorporating annual, perennial, or cover crops, support ecosystem services like carbon sequestration, pest control, and water protection, and can increase yields. However, long-term data is crucial to understand the full impact, and previous studies have focused on individual crops, missing broader rotational benefits. This study, analyzing data from multiple North American sites, found that while individual crops like maize and soybean benefit from rotational complexity, results for complete rotations depend on composition. Complex rotations also reduce crop loss risks in poor conditions. The study highlights that diversifying rotations may not harm yields and can help mitigate losses in challenging climates.

Results

Despite the dominance of simplified crop rotations in North American agriculture, the findings suggest that increasing rotational complexity can maintain or improve crop-level output with minimal trade-offs at the rotation level. By quantifying output on a financial basis, the study highlights the influence of highly productive crops and market valuation, shaped by government policies such as subsidies for maize-based biofuels and confined animal feed operations. Alternative metrics, including net returns, nutritive value, or environmental impact, may not favour simple rotations of just one or two crops. Measuring output in financial terms also reveals potential trade-offs, particularly during the establishment year for perennial forages, which sometimes leads to mixed results. These trade-offs should be considered when adopting more diverse rotations, especially without wider policy changes. Although the approach favours simplified systems, the findings show that under poor growing conditions, simplified rotations can perform worse than more complex ones, reflecting their reliance on subsidised crop insurance in the US.

Barriers to adopting more complex rotations include increased management complexity, the need for new equipment, and economic or psychological hurdles associated with growing less profitable crops on prime land. Limited local markets for crops such as small grains and perennial forages also discourage diversification. However, adoption could be promoted by building stakeholder networks that support diversification, along with broader strategies such as crop breeding and institutional reforms to remove economic barriers. New organisational forms, such as partnerships and legal frameworks, as well as growing interest in ecosystem services or carbon markets, could also support this transition, though the lack of consensus on environmental accounting remains a challenge.

Scaling up complex rotations requires policy reform. While the study shows mixed results at the rotation level using a financial approach, factoring in production costs and the environmental impacts of high-input systems could make lower-value crops more economically attractive. Additionally, higher market prices for perennial crops, such as those used for bioenergy or carbon capture, would further improve the outcomes of more complex rotations.