Arable Crops – Apply low-emission fertilizers

Apply low-emission fertilizers

System: Arable Crops

Not applicable or effective for: For application soil conditions need to be checked (see ‘Explanation of variable effect’). The effect on soil microorganisms is currently under research and debated – a systematic and frequent application should be considered carefully.

Description

Applying fertilisers, or products associated to fertilisers, which have been developed to better synchronize fertiliser N release with crop uptake (Enhanced-Efficiency Fertilisers). Examples are controlled-release fertilisers (CRF), urease inhibitors (UI) coupled to nitrogen fertilisers (organic or mineral), nitrification inhibitors (NI) coupled to fertilizers, and a combination of UI and NI (referred to as double inhibitors). Also nitrate leaching and therefore indirect N2O emissions can be reduced.

Mechanism of effect

Low-emission fertilizers offer the potential for enhanced N-use efficiency in crops and reduced N losses.

CRF release nutrients in a controlled manner (by diffusion through a coating), better matching nutrient release with crop demands and limiting availability of the fertiliser-derived N to nitrifiers and denitrifiers. Ammonium is also less susceptible for leaching.
UI delay the hydrolysis of urea into NH4+ by blocking the urease enzyme binding sites.
NI delay the bacterial oxidation of NH4+ (ammonium) to NO₂− (nitrite) and NO3- (nitrate), retaining mineral N as ammonium, which cannot be lost to the atmosphere by denitrification.

Reference situation

Conventional N fertilizer

Legend

● – Small effect (<5%)	● – small unfavourable effect (<5%)	o – No effect
●● – Medium effect (5-20%)	●● – large unfavourable effect (>=5%)	N/A – effect unknown
●●● – Large effect (>20%)	● – ● – Variable effect (depending on farm characteristics or way/level of implementation)

Effect on total greenhouse gas (GHG) emissions (kg CO2-eq)

	per ha		Level of evidence
	Mean	min-max
Controlled-release fertilizers (CRF)	●●	●●–●●●	High
Urease inhibitors (UI)	●●	●●–●●	High
Nitrification inhibitors (NI)	●●	●●–●●●	High
Double inhibitors (CRF with NI)	●●	●●–●●	Medium

Effect per emission source

Mean effect on emission from	Soil (per ha)	Inputs	Energy use
	N₂0	CO₂	CO₂
Controlled-release fertilizers (CRF)	●●●
Urease inhibitors (UI)	●●
Nitrification inhibitors (NI)	●●●
Double inhibitors (CRF with NI)	●●

*risk of an adverse effect (see ’cause of variable or unfavourable effect’)

Explanation of variable effect

Controlled-release fertilizers (CRF)

The effectiveness of controlled-release fertilizers (CRFs) is significantly influenced by environmental and crop-specific factors. Soil texture, temperature, and moisture levels affect how quickly nutrients are released, which can impact efficiency in different climates. Proper timing and application methods are critical to ensure nutrients are available when crops need them. Additionally, CRFs perform best when matched to the nutrient demands of specific crops and their growth stages.

Urease inhibitors (UI)

The effectiveness of urease inhibitors depends on various factors including soil pH, texture and organic matter content; application timing, temperature, and fertilizer management practices.

Nitrification inhibitors (NI)

The effectiveness of nitrification inhibitors (NI) is influenced by soil pH, texture, organic matter content, moisture, temperature, nitrogen fertilizer type and application rate, and the specific inhibitor used. Combined with urease inhibitor (UI), NI is a bit less effective than NI alone to cut N2O direct emissions but more effective to cut both ammonia (and so indirect N2O emissions) and N2O direct emissions.

Double inhibitors (CRF with NI)

The effectiveness of double inhibitors is influenced by soil and climatic conditions, fertilizer application rate and timing, crop type and growth stage, and nutrient management practices.

*Literature references*	Controlled-release fertilizers (CRF)
Thapa et al., 2016	Effect of Enhanced Efficiency Fertilizers on Nitrous Oxide Emissions and Crop Yields: A Meta-analysis
Akiyama et al., 2009	Evaluation of effectiveness of enhanced-efficiency fertilizers as mitigation options for N2O and NO emissions from agricultural soils: meta-analysis
Xia et al., 2016	Can knowledge-based N management produce more staple grain with lower greenhouse gas emission and reactive nitrogen pollution? A meta-analysis
Gao et al., 2017	Evaluation of the Agronomic Impacts on Yield-Scaled N2O Emission from Wheat and Maize Fields in China
Li et al., 2017	Enhanced-efficiency fertilizers are not a panacea for resolving the nitrogen problem
Eagle et al., 2017	Fertilizer Management and Environmental Factors Drive N2O and NO3 Losses in Corn: A Meta-Analysis
Mazzetto et al., 2020	Region-specific emission factors for Brazil increase the estimate of nitrous oxide emissions from nitrogen fertiliser application by 21%

*Literature references*	Urease inhibitors (UI)
Xia et al., 2016	Can knowledge-based N management produce more staple grain with lower greenhouse gas emission and reactive nitrogen pollution? A meta-analysis
Fan et al., 2018	The contrasting effects of N-(n-butyl) thiophosphoric triamide (NBPT) on N2O emissions in arable soils differing in pH are underlain by complex microbial mechanisms
Akiyama et al., 2009	Evaluation of effectiveness of enhanced-efficiency fertilizers as mitigation options for N2O and NO emissions from agricultural soils: meta-analysis
Wang et al., (2024)	Global Meta‐Analysis of Individual and Combined Nitrogen Inhibitors: Enhancing Plant Productivity and Reducing Environmental Losses. Global Change Biology, 30(12), e70007.
Fan et al., 2022	Global evaluation of inhibitor impacts on ammonia and nitrous oxide emissions from agricultural soils: A meta‐analysis. Global Change Biology, 28(17), 5121-5141.
Hasler, et al., 2017	Eco-innovations in the German fertilizer supply chain: Impact on the carbon footprint of fertilizers. Plant, Soil and Environment, 63(12), 531.

*Literature references*	Nitrification inhibitors (NI)
Thapa et al., 2016	Effect of Enhanced Efficiency Fertilizers on Nitrous Oxide Emissions and Crop Yields: A Meta-analysis
Xia et al., 2016	Can knowledge-based N management produce more staple grain with lower greenhouse gas emission and reactive nitrogen pollution? A meta-analysis
Li et al., 2017	Enhanced-efficiency fertilizers are not a panacea for resolving the nitrogen problem
Akiyama et al., 2009	Evaluation of effectiveness of enhanced-efficiency fertilizers as mitigation options for N2O and NO emissions from agricultural soils: meta-analysis
Gao et al., 2017	Evaluation of the Agronomic Impacts on Yield-Scaled N2O Emission from Wheat and Maize Fields in China
Feng et al., 2016	Integrated assessment of the impact of enhanced-efficiency nitrogen fertilizer on N2O emission and crop yield
Qiao et al., 2015	How inhibiting nitrification affects nitrogen cycle and reduces environmental impacts of anthropogenic nitrogen input
Cai et al., 2017	Effects of inhibitors and biochar on nitrous oxide emissions, nitrate leaching, and plant nitrogen uptake from urine patches of grazing animals on grasslands: a meta-analysis
Gilsanz et al., 2016	Development of emission factors and efficiency of two nitrification inhibitors, DCD and DMPP
Wang et al., 2024	Global Meta‐Analysis of Individual and Combined Nitrogen Inhibitors: Enhancing Plant Productivity and Reducing Environmental Losses. Global Change Biology, 30(12), e70007.
Fan et al., 2022	Global evaluation of inhibitor impacts on ammonia and nitrous oxide emissions from agricultural soils: A meta‐analysis. Global Change Biology, 28(17), 5121-5141.
Hasler, et al., 2017	Eco-innovations in the German fertilizer supply chain: Impact on the carbon footprint of fertilizers. Plant, Soil and Environment, 63(12), 531.

*Literature references*	Double inhibitors (CRF with NI)
Thapa et al., 2016	Effect of Enhanced Efficiency Fertilizers on Nitrous Oxide Emissions and Crop Yields: A Meta-analysis
Eagle et al., 2017	Fertilizer Management and Environmental Factors Drive N2O and NO3 Losses in Corn: A Meta-Analysis