LCA Food 2012 in Saint Malo, France! - Manifestations et colloques ...

PARALLEL SESSION 4A: CARBON FOOTPRINT 8 th Int. Conference on LCA in the
Agri-Food Sector, 1-4 Oct 2012
368
Estimating carbon footprints of individual crops in organic arable
crop rotations
Marie Trydeman Knudsen 1* , John E. Hermansen 1 , Jørgen E. Olesen 1 , Andreas Meyer-Aurich 2 , Ngonidzashe
Chirinda 1
1 Dept. of Agroecology, Aarhus University, Blichers Allé 20, Postbox 50, DK-8830 Tjele, Denmark
2 Dept. of Technology Assessment and Substance Cycles,Leibniz-Institute for Agricultural Engineerign, 14469 Potsdam, Germany
Corresponding author. E-mail: MarieT.Knudsen@agrsci.dk
ABSTRACT
Organic agriculture relies to a high degree on crop rotations, which interlinks the environmental impact of the crops. This constitutes
a challenge when using LCA for analysing organic products, specifically with regard to allocation aspects. This was studied in an
organic arable crop rotation experiment grown at three different locations in Denmark for three years. The aim was to compare the
carbon footprint of the crops at farm gate in four different crop rotations. The carbon footprints were estimated based on either a) the
full crop rotation or b) the individual crops. The last approach was done by splitting the environmental burden and benefits from e.g.
the green manure equally among the crops on a per hectare basis. The study highlights the importance of analysing the whole crop
rotation and including soil carbon stock changes when estimating carbon footprints of organic crops where green manure crops are
included.
Keywords: life cycle assessment, greenhouse gas emissions, organic, crop rotation
1. Introduction
Organic agriculture relies to a high degree on recycling of nutrients and using crop residues as a means to
fertilise crops and maintain soil fertility. Thus, the basket of products that originates from organic production
is diverse and to a high degree interlinked. This constitutes a challenge when using life cycle assessment
(LCA) for analysing organic agricultural products derived from the more complex systems. For example
with regard to allocation aspects when green manure crops or catch crops are included in the crop rotation.
Thus, while ISO standards for LCA (ISO 14040 and 14044) provide overall guidelines, there is still a need
for further development of LCA methodologies for complex systems such as organic agriculture. Furthermore,
the need to include soil carbon changes in the LCA of organic products is more urgent since organic
farming practices on average increase soil carbon sequestration (FAO, 2011).
The aim of the present paper is to explore and suggest a method to estimate the carbon footprints of individual
crops in organic arable crop rotations.
2. Methods
The challenge of estimating carbon footprints of organic crops was studied in an organic arable crop rotation
experiment grown at three different locations in Denmark for three years (2006-8). The organic crop
rotations were designed to explore ways to avoid the use of conventional manure. Organic arable production
is often in practice dependent on conventional manure, which is considered problematic by parts of the organic
sector in e.g. Denmark. Four different crop rotations were compared in the experiment in order to provide
alternative solutions to secure nitrogen (N) supply for the crops without using conventional manure.
2.1 The crop rotations
The four scenarios are illustrated in Figure 1; three organic (‘Slurry’, ‘No input’ and ‘Mulching’) and one
conventional crop rotation. The first organic scenario (Slurry) represents the present situation where slurry
(often conventional) is imported and used on arable farms and all four crops in the crop rotation can be sold
as sales crops. The second organic rotation (No input) represents a scenario where still all four crops can be
sold as sales crops, but no organic fertiliser is used. The third organic scenario (Mulching) represents a solution
where the faba beans are replaced by a green manure crop (grass-clover) that is incorporated in the soil
and thus only three sales crops can be sold from the rotation. Furthermore, a conventional rotation was included
that is similar to the ‘Slurry’ rotation, where all four crops can be sold as sales crops, but mineral
fertiliser is used instead of slurry and in addition pesticides are used. Where possible, catch crops were included
in the rotations (Figure 1).