The overall objective of this project is to identify the best option for animal slurry (liquid manure) application to soil in order to
maximize nutrient availability for plants and minimize the impact on losses to air (i.e greenhouse gases (GHG), nitric oxide
(NO) and ammonia (NH3) as well as transfers of nitrate-N (NO3-), ammonium-N, phosphorus (P), faecal pathogens
(Salmonella and Escherichia coli) and hormones (steroid) to waters.
More than 14 million tonnes of farm manures are applied to agricultural soils in Portugal each year. These inputs are a valuable
source of plant available nutrients (N and P) but also represent a significant risk of environmental pollution. Indeed, such
applications to soil may lead to important transfers of P and NO3- as well as faecal pathogens (Salmonella and Escherichia coli)
and hormones (steroid) to superficial and ground waters, On the other hand, they also induce an increase of gaseous emissions
Moreover, the Portuguese legislation includes a ‘closed-period’ for slurry application to soil in late autumn/winter. Hence, the
amount of slurry applied in the spring and summer months should increase with direct consequences on both the amount and
timing of nutrient losses to air and water.
Injection of slurry has proven to be efficient to decrease odours and NH3 emissions and has been adopted in many European
countries. However, recent studies showed that it may increase GHG emissions such as N2O and few is known about its impact
on diffuse pollution to water. Animal slurry management strategies defined to reduce one form of pollution (e.g. NH3 emissions
to air) have to take in consideration losses by other ways (e.g. NO3- to water) and prevent their worsening to avoid the so
called “Pollution Swapping”. On the other hand, pre-treatment of slurry by solid-liquid separation and acidification proved to be
efficient to decrease NH3 and GHG emissions after soil application. An application of the liquid fraction or acidified slurry rather
than untreated slurry using surface banding technique could therefore be as efficient as slurry injection.
Hence, the main question of the proposed work is: “Is animal slurry injection in soil more efficient to reduce the associated
environmental impacts and maintain the plant production level than a combined approach of slurry treatment followed by
surface banding application?”
To answer this question, we will use the following linked approach:
1. Estimate the leaching of nutrients (N and P), faecal pathogens and estrogens hormones following untreated slurry injection
or surface band application of pre-treated slurry;
2. Compare the nitrogen and phosphorous dynamics in soil as well as the plant production in soil amended by injection of
untreated slurry or by surface banding application of pre-treated slurry;
3. Compare the GHG and NH3 emissions at soil surface in soil amended by injection of untreated slurry or by surface banding
application of pre-treated slurry;
4. Evaluate the effects of the slurry application technique and slurry pre-treatment in beneficial soil microorganisms, namely
the effect on arbuscular mycorrhizal fungi and soil biological activity more directly involved in organic matter decomposition
and N2O emissions (nitrification or denitrification).
5. Evaluate the economic impact on the farm budget of the slurry management options under study.
This project will be conducted by four complementary research teams - ISA, UTAD, IPCB, and RRNW - composed of multidisciplinary
members (chemists, soil scientists, agronomists, microbiologists, air scientists).
Six master theses as well as one PhD thesis of one junior member of the research team will be prepared during this project
and the most relevant results will be published in refereed journals and presented at international meetings. Transfer of
knowledge to farmers, industry and decision makers will be a priority of the project and achieved by the organisation of a
national workshop and elaboration of a best management practices guide for a better slurry management. Indeed, the increase
of knowledge supplied by the proposed project is essential to improve the scientific evidence base that support proposals of
new strategies to minimise diffuse pollution to air and water. This integrated approach is fundamental to efficiently reduce
diffuse-pollution from animal manures at farm scale and help farmers to comply with national regulation (nº214/2008,
November 10th). Furthermore, it will help to scientifically justify any financial support to the agricultural activity to reduce
diffuse pollution and will also contribute to meet the national objectives of complying with existing and future protocols and
directives (e.g. Gothenburg Protocol, Kyoto Protocol, Nitrates Directive, and Water Framework Directive).