4R Nutrient Stewardship provides a comprehensive scheme to achieve multiple goals within cropping systems. These goals include increased production, farmer profitability, sustainability, and environmental protection.

Aligning 4R Nutrient Stewardship with Changing Farming Objectives

The 4R concept is based on four critical factors that aim to optimize the application of fertilizers: the right fertilizer source used at the right rate, right time, and right place. By applying fertilizers according to these principles, they can significantly contribute to the economic, social, and environmental benefits of cropping systems.

As farming objectives evolve to support sustainability outcomes, 4R Nutrient Stewardship needs to adapt and integrate with these changes. Based on our previously published new paradigm for Responsible Plant Nutrition, we identified six key actions to integrate into 4R Nutrient Stewardship:

• Nutrient Roadmaps: Integrate 4R practices into policies, business models, platforms, and programs to verify sustainability efforts.
• Digital Solutions: Leverage data-driven technologies to make more precise and dynamic 4R nutrition decisions.
• Recycling: Optimize the utilization of renewable nutrient resources by considering recycled forms where feasible.
• Nutritious Crops: Promote crop nutrient applications to enhance human nutrition and health.
• Climate-Smart Fertilizers: Consider the carbon footprint of nutrient sources including emissions associated with both manufacturing and use.
• Accelerated Innovation: Test 4R components through adaptive management systems to facilitate faster translation into practical farming practices.

Overcoming Barriers and Advancing 4R Nutrient Stewardship

The concept of 4R Nutrient Stewardship has gained global recognition while its impact remains different around the world. Regional implementation of 4R practices and challenges associated with its progress differ considerably across continents.

This global disparity seems to be due to several challenges that prevent the widespread adoption and quantification of the benefits of 4R Nutrient Stewardship. To overcome these challenges and ensure successful 4R implementation, we propose the following new core principles for fertilizer application:

• Supply nutrients in quantifiable and available forms. Nutrients can be released be immediately or slowly. Yet, the amount of plant-available nutrients must be known if crop requirements are to be met.
• Use climate-smart forms. Climate-smart fertilizers emit less greenhouse gases, both during manufacture and post-application. Future “Smart Fertilizers” could include nanoparticulate forms of nutrients, aptamers, and coatings, releasing nutrients in response to microbial activity and plant demand.
• Use recycled forms where feasible. Applying manures, biosolids, and composts reduces the need for manufactured fertilizers while lowering the total environmental footprint. On farms importing livestock feed, however, nutrients in the manures may exceed crop requirements.
• Consider biological inoculants. Biofertilizers are defined as living microbes that enhance plant nutrition by mobilizing or increasing nutrient availability in soils. Various beneficial bacteria and fungi are used as biofertilizers, colonizing the rhizosphere, rhizoplane, or root interior.
• Address variability in crop response. Incorporating weather in the decision process for nutrient rates can improve crop production outcomes.
• Address changes in nutrient needs through the growing season. Dynamic adjustment of nutrient applications during the growing season is feasible in several cropping systems.
• Place nutrients to avoid loss. Correct spatial placement of nutrients across the landscape can minimize off-site losses of nutrients.

4R Nutrient Stewardship for sustainable food systems

Collaborative efforts among stakeholders are crucial to drive the progress of 4R Nutrient Stewardship. That’s why we propose stakeholders take actions:

• Fertilizer industry: Implement decision support systems and recommendations for choosing the right source, rate, time, and place according to the 4R framework.
• Fertilizer retailers, agri-service providers, and crop advisers: Provide farmers with evidence-based information on specific 4R practices and responsible agronomic practices.
• Farmers and other fertilizer users: Optimize nutrient management with available source-rate-time-place combinations, based on crop needs and soil fertility conditions, and using appropriate decision support tools.
• Scientists: Work with crop advisers and farmers, define and describe 4R practice standards relevant to more regenerative farming systems.
• Governments: Facilitate the collection of statistical data at a greater level of detail to support reporting of 4R practices.
• Food traders, processors, and retailers: Recognize and reward 4R practices on products.
• Civil Society Organizations: Advocate recognition and rewarding of 4R Nutrient Stewardship in collaborative platforms advancing sustainable agriculture.
• Investors: Invest in technologies, businesses, and organizations that support 4R as a recognized means of advancing nutrient stewardship.

We suggest embracing the 4R framework and responsible plant nutrition to create a more sustainable and resilient agriculture. This will benefit farmers and the environment alike.

This Issue Brief presents a fundamental pathway to address food security, environmental conservation, and climate change challenges, leading us toward a prosperous and sustainable agricultural landscape. We hope to make an impact in advancing 4R Nutrient Stewardship, fostering regenerative practices that protect biodiversity, enhance productivity, and contribute to a circular and climate-smart agricultural sector.