Chapter 4 summary

Opportunities for better phosphorus use in agriculture

Chapter authors: Cargele Masso, Fusuo Zhang, Tapan K. Adhya, Martin S.A. Blackwell, Katrina A. Macintosh, Penny J. Johnes, Phil M. Haygarth, Paul J.A. Withers, Gu Feng, Haigang Li, Chaochun Zhang, Jiechen Wu, Jianbo Shen, Marc I. Stutter, Lingyun Cheng, Will J. Brownlie • 10min read

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Chapter highlights

Low phosphorus use efficiency (~20%) and high phosphorus losses from agricultural land to waterbodies is a growing global problem and exacerbated by climate change and rainfall extremes. Fertiliser use can be optimised and should consider all nutrients. Widespread soil phosphorus testing is required. In some regions appropriate control limits on phosphorus inputs will be needed, whilst in others an increase in P inputs will be required to improve/maintain agricultural productivity. An integrated approach to improve phosphorus use efficiency, reduce losses and increase recycling throughout the food production and consumption chain is needed. A multi-stakeholder approach will, therefore, be critical.

Introduction

How can we increase phosphorus use efficiency in agriculture?

Sustainable agriculture must balance the priorities of environmental quality, human health, economic profitability, and social equity, and rests on the principle that our current needs (e.g. short term economic gain) should not compromise the ability of future generations to meet their own needs. Sustainable management of phosphorus and other nutrients is an essential component in delivering these priorities. Low phosphorus use efficiency and high phosphorus losses from agricultural land to waterbodies is a growing problem globally and this is exacerbated by climate change and rainfall extremes. In regions where access to phosphorus fertilisers is not a limiting factor, there is a trend to apply high rates of phosphorus to compensate for soil phosphorus fixation, increasing potential phosphorus losses from agricultural soils. Meanwhile in some low-income countries, insufficient use of fertilisers and soil erosion has led to substantial nutrient depletion of soils - this constrains agricultural productivity, which especially impacts on marginal and smallholder farmers.

Livestock systems are the major cause of phosphorus inefficiency in regional and national food systems because of the additional phosphorus inputs required to produce the large amounts of home-grown feed consumed by animals, particularly ruminants. In a recent global assessment of phosphorus use efficiency in agriculture, the overall agricultural production system (averaged as 46%) was lower compared to the crop-pasture subsystem (averaged as 72%) but higher than the livestock subsystem (averaged as 18%). Whilst agricultural systems differ, poor phosphorus management is widespread and a significant cause of avoidable phosphorus surpluses and losses.

Targets to increase phosphorus use efficiency in agriculture and indicators to monitor improvement are needed and should be aligned within a multi-stakeholder approach to improve phosphorus use efficiency throughout the food-production chain. Catchment management plans should be developed, that maximise synergies with other nutrients (e.g. nitrogen) and are adaptive to accommodate the various changing pressures on the agricultural system, including climate change, population growth and economic development. Implementing the most effective measures to improve phosphorus use efficiency and phosphorus sustainability in agriculture requires an integrated management approach. This will require knowledge exchange and collaboration between stakeholders to address the different ecological, economic, and societal aspects of phosphorus management.

Fortunately, measures that reduce phosphorus losses and improve phosphorus use efficiency in agriculture are a ‘win-win’, as they aim to increase food production by reducing the need for external phosphorus application. This can improve food security, reduce phosphorus transfer to waters and associated eutrophication and, in some regions, reduce costs wasted on the application of excess phosphorus fertilisers (including animal wastes). Enhancing phosphorus use efficiency and increasing phosphorus recycling across sectors will have multiple benefits, including mitigating other pollutant emissions (e.g. nitrogen and carbon dioxide), boosting the standardisation and development of nutrient-rich waste management, and supporting business development opportunities associated with the innovation of phosphorus fertilisers and related novel technologies. In this way, addressing phosphorus sustainability in agriculture delivers on multiple United Nations’ Sustainable Development Goals, including poverty alleviation (SDG1), zero hunger (SDG 2), clean water/sanitation (SDG 6), responsible consumption and production (SDG 12), life below water (SDG 14), and life on land (SDG 15).

In the following section, the key challenges in achieving high phosphorus use efficiency in agricultural systems are discussed, followed by solutions that will help to deliver a more sustainable use of phosphorus in the production of crops and livestock.

Key issue 4.1

Low phosphorus use efficiency and high phosphorus losses are common in agriculture

The challenge

Low phosphorus use efficiency (~20%) and high phosphorus losses from agricultural land to waterbodies is a growing problem globally and is exacerbated by climate change and rainfall extremes. In some cases, slow/controlled-release fertilisers can improve phosphorus use efficiency but these are not yet widely used. In regions where access to phosphorus fertilisers is not a limiting factor, there is a trend to apply high rates of phosphorus to compensate for soil phosphorus fixation, which can increase potential losses. Improving the utilisation of residual phosphorus in soils is critical for achieving efficient agricultural phosphorus use in these regions.

The solution

Farmers should not apply more phosphorus than needed to maximise crop yields. Fertiliser use can be optimised and should consider all nutrients. Soil phosphorus testing and appropriate control limits on phosphorus inputs may be needed. In some regions, such as parts of Africa, more phosphorus should be applied to improve/maintain crop productivity. Slow-release fertilisers, structural farming measures to reduce erosion and run-off and, innovations to improve uptake of residual phosphorus stores may reduce phosphorus losses whilst maintaining yield. Training farmers and advisors in nutrient management and providing access to decision support systems/tools for nutrient budgeting are required.

Key issue 4.2

The complexity of soil-crop phosphorus cycles can confound management efforts

The challenge

The phosphorus cycles that underpin organic, intensive monoculture and mixed farming systems vary widely and are sometimes poorly understood. This can make crop uptake of phosphorus difficult to predict, resulting in poor estimates of fertiliser requirements that may confound attempts to improve phosphorus use efficiency.

The solution

Multiple strategies can be used to optimise the phosphorus use efficiency of crops, through site-specific modifications to crop management, integrated soil fertility management (including water and weed management), rhizosphere management and the use of phosphorus efficient cultivars and bio-fertilisers. Strategies can now be developed to improve plant uptake of applied and residual phosphorus in the soil.

Key issue 4.3

Livestock in intensive farming operations are often fed phosphorus in excess leading to high excretion rates

The challenge

Demand for animal products is increasing. In some regions, poor management (i.e. collection, storage, and application) of animal manures leads to avoidable phosphorus losses to waterbodies. Furthermore, livestock and poultry are commonly fed more phosphorus than they can utilise, leading to the excretion of phosphorus-rich manures; they typically retain less than 30% of the phosphorus ingested.

The solution

Optimising the diets of animals in intensive farming operations to match growth requirements, and supplementing monogastric animals with phytase enzymes can reduce phosphorus excretion. Balancing P and other nutrients in diets as a front-end nutrient management approach has the advantage of lowering phosphorus surplus on farms and subsequently reducing potential environmental losses and saving producers’ money in feed costs. Governments should provide guidance on recommended dietary phosphorus allowance for livestock based on current scientific knowledge.

Key issue 4.4

Recycled phosphorus is not sufficiently used in agriculture

The challenge

A circular approach to phosphorus management in agriculture is critical to address the significant amounts of phosphorus currently lost to the environment or landfills. Recycling is currently limited by transport costs of recycled resources and decoupling of phosphorus cycles across agricultural sectors due to intensification of livestock production. Policies and negative public perceptions about the safety of use can limit phosphorus recycling of certain wastes and residues. Phosphorus recovery must produce contaminant-free phosphorus materials for safe reuse in recycled fertilisers.

The solution

Globally, recycling of treated animal manures and residues and the use of recycled fertilisers should be increased, with corresponding reductions in mineral fertiliser use. Integrating arable and livestock systems can help to reduce costs associated with transporting phosphorus-rich animal manures and materials to crops. In some cases, education, extension services and investment in infrastructure and technology are needed to support stakeholders and make phosphorus recycling more efficient.

Key issue 4.5

There are insufficient policies and targets to deliver integrated action on phosphorus

The challenge

Policies and/or regulations relating to sustainable phosphorus management at national or regional scales are sparse, and none exist at the global scale. Where regulations exist, policy incoherence and weak enforcement due to the lack of coordination among relevant ministries is commonly observed. Aspirational goals/targets (e.g. for phosphorus recycling, phosphorus losses, phosphorus use efficiency) and indicators to monitor improvement are also lacking for most regions.

The solution

An integrated approach is essential to increase sustainable phosphorus use in the agricultural sector and will require actions across scales, sectors, disciplines, and regions. Targets to increase phosphorus use efficiency in agriculture and indicators to monitor improvement from farm to global scales are needed. Phosphorus budgets at the farm scale are needed to develop catchment management plans that scale phosphorus use efficiency assessments to national, regional, and global scales. We must maximise synergies with other nutrients and ensure that policies are adaptive.

Conclusion

Improving phosphorus use efficiency in crop and livestock production requires a combination of strategies that are appropriate for both addressing local and regional issues. Multiple strategies can be used to optimise phosphorus use efficiency of crops, through site-specific modifications to crop management, integrated soil fertility management, rhizosphere management and the use of phosphorus efficient cultivars and bio-fertilisers. Fertiliser use can be optimised and should consider all nutrients. Widespread soil phosphorus testing is required. In some regions appropriate control limits on phosphorus inputs may be needed, whilst in other regions an increase in P inputs to soils will be required to improve/maintain agricultural productivity. Slow-release fertilisers, structural farming measures to reduce erosion and run-off, and innovations to improve uptake of residual phosphorus stores may reduce phosphorus losses whilst maintaining yield. Optimising the diets of animals in intensive farming operations to match growth requirements and supplementing monogastric animals with phytase enzymes can reduce phosphorus excretion. Globally, recycling of treated animal manures and residues and the use of recycled fertilisers should be increased, with corresponding reductions in mineral fertiliser use. However, targets to increase phosphorus use efficiency in agriculture, and indicators to monitor improvement are needed at national, regional, and global scales. Policymakers are encouraged to promote good phosphorus management practices by developing and implementing enabling policies. In some cases, financial instruments such as subsidies, tax incentives, and support for farmers to adopt sustainable measures will be required. An integrated approach to improve phosphorus use efficiency and reduce losses throughout the food production and consumption chain is needed; a multi-stakeholder approach will, therefore, be critical. However, phosphorus sustainability strategies will need to be adaptive to meet the changing pressures of climate change and population and economic growth.

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The full chapter contains references to the evidence provided above and acknowledgements of images.

Suggested citation for this chapter: C. Masso, F. Zhang, T.K. Adhya, M.S.A. Blackwell, K.A. Macintosh, P.J. Johnes, P.M. Haygarth, P.J.A. Withers, G. Feng, H. Li, C. Zhang, J. Wu, J. Shen, M.I. Stutter, L. Cheng, W.J. Brownlie. (2022) Chapter 4. Opportunities for better phosphorus use in agriculture, in: W.J. Brownlie, M.A. Sutton, K.V. Heal, D.S. Reay, B.M. Spears (eds.), Our Phosphorus Future. UK Centre for Ecology and Hydrology, Edinburgh. doi: 10.13140/RG.2.2.31727.71846

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