Download Agricultural nutrient problems and the MAP IV water quality goals

VISION TEXT
Agricultural nutrient problems and the MAP IV water quality goals: Research needed to
prepare for MAP V
Research and Extension Advisory Board on Sustainable Fertilisation 26/10/2012
Background
Previous efforts to improve the quality of ground and surface water have obviously resulted in
improvements, but in several regions in Flanders, the 50 mg nitrate per litre norm from the European
Nitrate Directive (91/676/EEC) and water phosphorus quality norms for different water types from
the Water Directive (2000/60/EG) have still not been achieved. To effectively further decrease
nutrient losses from plant production, the fertilisation norms have been tightened and other
measures were also included in the fourth manure action plan (MAP IV). These measures lead
farmers and horticulturists to make extra efforts and adjust their management. MAP IV also includes
several accompanying regulations to help the farmers and horticulturists to maintain the profitability
of their enterprise while operating within the new norms and preconditions and to work toward the
environmental goals. However, knowledge is still lacking about how precisely to achieve the
environmental goals, obtain optimal yield and quality, and also to maintain soil quality.
As part of the policies in MAP IV meant to help farmers, the research and advisory board on
sustainable fertilisation was created. The advisory board consists of research centres, universities,
university colleges, research institutes and government agencies. The specific tasks of the advisory
board are to inventory and prioritise research needs, to document research and extension themes, to
develop a research strategy for sustainable fertilisation that can be translated into practice, and to
advise the policy planning agency.
During the discussion about MAP IV, Flanders and the European Commission’s DG Environment
agreed on the need for further applied scientific research on catch crops after grains, nutrient
management in horticulture, fertilisation norms as documented by field research, and the
phosphorus problem. The advisory board met to discuss the research priorities set out by Europe
about catch crops and horticulture. After this consultation, various research projects were started in
2011 and 2012 by order of the Flemish Land Agency (VLM).
Methodology
The advisory board met on June 7, 2012. During that meeting, various members of the research and
advisory board on sustainable fertilisation could propose additional research needs on the
agricultural nutrient problem in the context of the MAP IV water quality objectives. We made an
inventory of the gaps in knowledge about how to sustainably fertilise while striving to meet the
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water quality goals and, at the same time, ensuring optimal yield, product quality and soil quality.
Frequently mentioned and linked research needs were united across all agricultural sectors and
prioritised. Based on this input, a vision text on the research priorities was written. In the meeting of
September 25 2012, the vision text on the research priorities for nutrient problems in agriculture was
discussed, additions were made, and the document was finalised.
Striving to meet the water quality objectives in MAP IV and preparing for MAP V: Knowledge gaps
and need for further research on agricultural nutrient problems
Phosphorus problems
Many years of phosphate surpluses have resulted in a large area of phosphate-saturated agricultural
soils in Flanders, high fractions of phosphate in solution and increased phosphorus (P) losses to
ground and surface water. Currently the orthophosphate concentration in the surface water of the
Flemish MAP measuring points is on average 3 times higher than the established norm.
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Risk of phosphorus losses from different soil textures
Across Flanders, excessive concentrations of orthophosphate have been measured in the surface
waters. In the medium term, the phosphorus problem will probably become more important than
the nitrogen problem. A protocol for measuring a high risk of P leaching and accompanying stricter
P2O5 fertilisation norms exist, but only for phosphate-saturated sandy soils. For non-sandy soils, no
protocol exists to clearly and simply indicate the link between the P amount in and the risk of P
losses. Such a protocol is necessary to evaluate a high risk of P losses from all soil textures and to
examine if there is a scientific basis for differentiation of the P2O5 fertilisation norms. Fundamental
research is therefore needed to understand the complex P chemistry in different soil textures, which
eventually results in P losses.

Field measures needed to address the phosphorus problem
Cost-effective field measures are necessary to reduce P losses and to improve water quality. To
reduce the losses from agriculture, the P2O5 fertilisation norms of MAP IV are lower than the P
exported by the different crops. By creating a negative balance, the P in the soils will be mined
gradually. This may enable large-scale reductions in P leaching to surface water. This is a long-term
process, however, unless P input would be drastically reduced. The economic effect of this would be
very difficult and would be a delicate exercise. It is still unknown how the mining process effects the
direct P availability. An improved utilisation of the phosphate stock in the soil could ease the effect of
the lower fertilisation norms. Both chemical (e.g. local decrease of soil pH) and biological methods
(e.g. phosphate solubilising bacteria (PSB), mycorrhiza) have the potential to affect the P availability
(near the roots).
Other alternative options to fix P in the soil include increasing the soil’s phosphate adsorption
capacity (FAC) or fixating P - e.g. in drains or buffer strips – before it leaves the field. For these three
options it is important not only to research the effect on the environment but also to understand the
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effect on crop yield and quality as well as the possibility of, or need for making P available during
early plant growth.
Soil organic matter maintenance within the current legislation
Soil quality depends in part on a sufficient amount of soil organic matter (SOM). Therefore organic
matter (OM) has to be regularly applied to the soil because crop residues are not enough to
compensate for the mineralisation from SOM. The manure decree restricts the maximal allowed
application of nitrogen (N) en P per hectare and per year in function of the different crop groups. The
lower application of OM due to the MAP legislation has had an important impact on the structure
and composition of SOM. In MAP IV, the introduction of fertilisation norms based on effective N
gives the farmer the opportunity to use organic manures, which are a valuable source for the
construction of SOM. However, research is needed on carbon (C) rich organic manures with an
optimal C/N/P ratio for the supply of effective organic matter with minimal N and P losses. If the N
mineralises at a time where there is no N need (wintertime), there is a risk for N leaching. It is very
important to know the N and P working coefficients and long term mineralisation of organic manures
to accurately evaluate the N supply during the growing season and their effect on the nitrate
nitrogen residue in the autumn. This requires additional research.
In the system analysis of the correlation between soil quality and condition and the dynamics of the
nutrients N and P, it is important to better understand the relationship between fertilisation
(history), crop rotation and (improvement of) soil quality. Knowledge is still needed about the
correlation of soil quality and condition with the nutrient efficiency of the applied fertilisers and with
the nutrient buffer capacity and losses. We also recommend further study of the impact of different
factors (weather, soil type, soil condition, use of farmyard manure, etc.) on the nutrient dynamics in
the soil. It is important to research the possibilities to adjust the mineralisation and release of N and P
at the appropriate time. The accurate assessment of the N mineralisation, especially from soils which
have been supplemented with different types of organic manures, remains the most uncertain factor
in calculating correct fertilisation advice.
Nutrient uptake and dose response curves of arable and horticultural crops
Scientifically sound fertilisation advice accounts for both optimal yield and quality, as well as the
water quality objectives. To fine-tune the nutrient amount and timing of fertilisation in fertilisation
advice, it is important to update the yield and N and P uptake of the arable and horticultural crops.
To refine the N top dressing of horticultural crops it is essential to have a correct idea of the N uptake
pattern during the entire growing period and the necessary amount of nitrate nitrogen in the soil
until harvest.
During the negotiations about MAP IV, the maximal allowed amounts of N (= fertilisation norm) were
based on a theoretical N balance method. The European Commission has also requested a practical
substantiation of the model based on dose response curves from field research.
New field experiments with different fertilisation steps are required to determine the optimal N and P
uptake of arable and horticultural crops, the N and P uptake patterns and necessary mineral N in the
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soil during the growing period of horticultural crops, and the N losses during the winter period. This
information is essential to further optimise the N fertilisation of agricultural and horticultural crops
and factually document the fertilisation norms. A protocol must first be developed for the (minimal
amount of data needed for) fertilisation experiments in order to develop fertilisation advice as well
as fertilisation norms.
Buffer strips
The construction and installation of buffer strips is a measure to improve the water quality but is also
designed to realise a number of other objectives, i.e. conservation objectives and objectives for
projects in the framework of integrated water policy. The collection of research results on buffer
strips and translation to Flemish agricultural and horticultural practice are needed to optimise the
extension education efforts.
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