Grassland management as a measure for the reduction of methane & ammonia emissions

Due to different growing conditions based on soil type, season and weather, and differences in use or management such as grazing systems and mowing regimes, a wide range of grass qualities is created. ,. It makes a difference to the quality whether you feed grass as silage grass, fresh meadow grass or through summer barn feeding and whether this grass is long or short and is offered in the spring or in the autumn. The grass quality has a direct effect on the emissions of methane and ammonia. Grassland products can therefore no longer be seen as a uniform product in emission calculations.

Grassland is the basis of dairy farming. Grassland management has a direct effect on the quality of the ration and thus on emissions from dairy cattle, but is not yet used as a control mechanism. It is therefore necessary to understand the mechanisms that cause CH4 and NH3 emissions in order to subsequently be able to manage them simultaneously. This is necessary in order to offer dairy farms concrete tools that contribute to a reduction in both CH4 and NH3.

Background

The mechanisms surrounding NH3 in relation to (fresh) grass are reasonably clear and can mainly be managed with a lower protein content (and more resistant and less unstable protein) and a higher energy content. The mechanisms surrounding CH4 in relation to (fresh) grass are less well understood. These seem to be mainly driven by a higher digestibility, which is strongly linked to the harvest stage and time in the season. Relationships and effects of CH4 reduction in relation to reduction of NH3 have not yet been fully tested when it comes to variation in grass quality and grass composition (legumes and herbs).

What do we research?

The aim of this project is to quantify the control mechanisms based on grassland management for methane emissions, so that in practice better calculations can be made for a simultaneous reduction of CH4 and NH3. To do this, the following research questions must first be answered

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1. How do the CH4 and NH3 emissions relate to grass silage, fresh grass in the stable and pastures?

2. What is the effect of grass age (NDF) on CH4 and NH3 emissions from pastures?

It is expected that the ranking in CH4 and NH3 emissions may change during the season of grass silage, fresh grass in sheds and pastures due to changes in grass quality (young spring grass compared to older oversized grass around June), but that the spring pasture grass and possibly also autumn meadow grass leads to lower CH4 emissions. In addition, it is expected that we will be able to control NDF and RE content by means of growth time, which will allow us to reduce NH3 emissions without negative shifting towards CH4 emissions.

Why is this important?

There are concrete starting points for arriving at an integrated approach to the reduction of NH3 and CH4 on dairy farms through the feeding of grass if the management of grassland is used as a control mechanism. To do this, it is necessary to identify and quantify these control mechanisms on the basis of this more fundamental research. The practical measures that follow from this will be deployed in an adjacent practical network of dairy farmers. The perspective is to use the grass in such a way and to influence / control the grass quality through cultivation, fertilization and harvest in such a way that NH3 and CH4 emissions are both reduced. On the one hand due to the choice of grassland use as pastures, summer barn feeding or silage grass. On the other hand, both via grass silage by influencing the time of harvest and the silage process and as fresh grass through grazing management.

What activities do we carry out?

Various trial plots with grassland have been set up at the Dairy Campus research location. In April, June and August we measure the methane emissions from grass silage, fresh grass in the barn and grazing day and night in three groups of 16 cows. In May, July and September we measure the methane emissions from short pasture grass (approx. 900 kg DM / 8 cm) and from longer pasture grass (approx. 1700 kg DM / 15 cm). In this way, insight is gained into the various forms of grassland use, but also a picture of seasonal effects is created. The research will be conducted for several years.

This project is part of a larger network of Climate Envelope projects commissioned by the Ministry of Agriculture, Nature and Food Quality.