3KFD4949

3275

15 janvier 2021 10:05

12 avril 2021 18:03

Biological nitrogen fixation in leguminous plants can be used to reduce the synthetic nitrogen (N) fertiliser requirements of arable cropping systems. Inserting full-year grown forage legumes in a crop rotation can provide N to subsequent crops through legume crop residues by its residual N effect, but also by processing the harvested forage legume into an organic fertiliser. This study aimed to quantify the N supply potential of forage legumes to an arable crop rotation in a temperate climate and their land requirements. Three scenarios of alternative legume-based fertilisers were taken to assess the N fertilisation effect, being a) alfalfa silage, b) grass-clover based cattle slurry, and c) alfalfa-based biogas digestate. Regarding crop management, good growing conditions for the forage legume crop were assumed, as well as frequent cuts and no additional N fertilisation to aim for a high N fixation. The N fertilisation effects were calculated by two different approaches, being 1) the static approach, that presents a static model of equations to calculate the N effects, for which literature data was used, and 2) the dynamic approach, that used the crop rotation model NDICEA to model the N flows in a crop rotation, from which the N effects were calculated. The results showed that alfalfa was able to fix 625-685 kg N/ha/y in its above- and belowground parts, which was higher than the 302-480 kg N/ha/y for grass-clover. For both crops, 40% of the total plant N was assumed to be allocated to the residual parts. Processing the harvested forage legume into silage or biogas digestate showed potential of retaining 90-93% of N in the fertiliser, whereas this was only 50% when processed into cattle slurry. The total N fertilisation effects, equivalent to synthetic N fertiliser, were calculated as 392-582 kg N/y per hectare of alfalfa in the static and dynamic approach, whereas this was lower and more uncertain for grass-clover based cattle slurry with 127-382 kg N/ha/y. To replace synthetic N fertilisers in an intensive arable cropping system by alfalfa, 25-37% additional land area would be required to maintain similar yields, which equals to a 20-27% share of total agricultural land. This however assumes that the full-year forage legume is the only N source, whereas the land requirements could be reduced by using other N sources, such as captured residual flows or implementing leguminous cover crops or main crops in the rotation. Overall, using full-year forage legumes as N source provides a natural alternative for using synthetic N fertiliser which fits in a context of circular agriculture, but this comes at a substantial cost of land area.

None

• AB - Utile à l'AB
• FREDO fertilisation
• FREDO rotation culturale
• GEO Pays-Bas
• azote
• légumineuses
• nitrogen
• économie circulaire

11/2020

1 novembre 2020