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FFL-JA-Forskningsmidlene for jordbruk og matindustri

Mitigation of greenhouse gas emission from cropped soils by mafic mineral applications

Awarded: NOK 0.81 mill.

The aim of the MIGMIN project is to investigate if N2O emissions from farmland can be reduced by increasing the soil pH (counteract acidification). This will reduce the climate forcing of food production because N2O is a strong climate gas which accounts for much of the total climate forcing by agriculture. Regular liming of farmland is recommended in order to counteract acidification. The reason is that most crop plants grow poorly in very acidic soil. It is possible, however to achieve good crops even on relatively acidic soils, because the minimum-pH for several crop plants is rather low (pH 5.5-6). The idea behind the MIGMIN project is that pH in farmed soils should be increased beyond the minimum pH for the crop plants, in order to reduce the emission of N2O. The rationale for this is that the N2O production by denitrification decline with increasing pH. We have previously shown that this is because the synthesis of the enzyme N2O reductase, which reduce N2O to harmless N2, increase with soil pH in the interval 4-7. The downside of liming is an immediate emission of CO2 (carbonate-CO2). We have searched for alternative minerals to replace carbonate, and have investigated the dissolution rate and pH-effect of of mafic minerals from the Norwegian Mineral industries. The results show that the dissolution rate is marginal, even under favorable conditions (low H, high microbial activity), and so is the effect on soil pH. We conclude therefore, that carbonate is the only option, and have achieved 30-50 % reduction of the N2O emission by using dolomite and colloidal marble from OMYA Although denitrification is the dominating source of N2O, small amounts are also produce by nitrification (ammonium oxidation). Our research demonstrate that liming stimulates this N2O production by nitrification, because it favors ammonium oxidizing bacteria (AOB) over ammonium oxidizing archaea (AOA), and AOB produce more N2O than AOA. Our field experiment demonstrate that the overall effect of liming is to reduce N2O emission, reflecting that denitrification is the major source of N2O in intact agroecosystems. This means that intensified liming will reduce the N2O emission from Norwegian farmlands, in particular from acidified grassland soils. The downside of this is of course the immediate emission of carbonate-CO2. The climate effect of this is uncertain, however, because the more long term effect of liming is carbonate formation elsewhere in the ecosystem. Our field experiments demonstrate a 30-50% reduction of N2O emission by liming, which reflect that denitrification is the dominant source of N2O in soil. This leaves little doubt that Norway will be able to reduce the total N2O emission by intensified liming, in particular in areas with grass production on acidified soils. The costs, in terms of climate forcing, will be an immediate emission of carbonate-CO2. This effect of liming is uncertain however, because it will be counteracted by the secondary stimulation of carbonates.

Styrket kobling mellom grunnleggende og agronomisk forskning: MIGMIN har styrket vårt agronomiske nedslag gjennom etablering av omfattende feltforsøk, og implementering av robot-teknologi for effektiv måling av N2O- og CO2- emisjon fra agronomiske feltforsøk. Styrket finansiering av forskning på nitrogen Forståelse av hvordan pH påvirker N2O emisjon har økt internasjonal interessen og resultert omfattende internasjonalt samarbeid, gjesteforskning ved NMBU, og etablering av et europeisk FACCE ERA-GAS prosjekt Nærmere samarbeid med næringslivet MIGMIN har bidratt til å etablere nært samarbeid med næringslivet Reduksjon av N2O emisjon fra landbruket MIGMIN har lagt et grunnlag for å lansere kalking som et probat tiltak for å redusere klimagassutslippet fra landbruket. Karbonat-frie bergarter har liten virkning Prosjektet har dokumentert at karbonatfrie avgangsmasser fra norsk bergverksindustri er ubrukelige som middel for å heve pH i landbruksjord.

Mitigation of N2O emission from cropped soils appears difficult; existing recommendations are limited to general optimization of nitrogen and soil management ("good agronomic practice"). We will explore a novel approach to reduce both N2O and CO2 emission s. By using powdered mafic rock as a replacement of lime to secure moderately high pH in cropped soils, we expect a triple effect on the greenhouse gas emissions: a. The emission of CO2 from lime is eliminated (mafic rocks do not contain carbonate) b. The weathering of the mafic rock material will result in CO2 sequestration as carbonate c. The emission of N2O will be reduced Effect a) is obvious, b) is questionable on a short time scale, and c (reduction of N2O) is based on recent research which has unr aveled a pervasive effect of soil pH on the N2O/(N2O+N2) product ratio of denitrification in soils sampled worldwide, AND a mechanistic understanding of the reasons for this. A first proof of concept (hypothesis c) has been provided in laboratory scale e xperiments as well as in preliminary field experiments. We will continue with laboratory experiments to compare the effect of different minerals and pretreatments on C- and N-transformations. Pretreatments of mafic minerals to enhance their reactivity hav e been developed for other purposes (one patented), and the knowhow and techniques developed will be a point of departure for designing pretreatments that enhance the reactivity of mafic mineral particles in soil. Field experiment will be established to e valuate the effects of mafic rocks versus lime on crop production and N2O emissions under realistic agronomic conditions. Effects on crop performance and trace metal uptake in plants will be studied in adjacent experiments in collaboration with other rese arch groups (Agropro). The project team includes expertise on mineralogy, industrial processing, geo/soil biology and microbial N-transformation.

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FFL-JA-Forskningsmidlene for jordbruk og matindustri