The fertilisation process enhances the land by spreading natural or chemical fertilisers. Thus many nitrate fertilisers are used to enrich the soil with nitrogen, necessary for good forage production.
Livestock faeces are commonly used for fertilisation, since they have advantage of being rich in nitrogen and are produced on site. They are spread on the farm plots enabling non-excess nitrogen balance.
The hidden side of this nitrogen balance is uneven distribution of this manure over the cultivated surface of the farm. Cornfields are regularly over-fertilised whilst pastures often do not receive any manure. This over-fertilisation of certain zones leads to significant risks of pollution by releasing a nitrogen surplus in the soils, into the atmosphere and into waterways.
It is important to recall that over-fertilisation does not improve production nor the yield of a cultivated surface compared to an optimal fertilisation. If the optimal fertilisation of a crop is 300 kg of spread manure, using 350 kg or 700 kg will not improve the yield of this crop.
Rebalancing the Spreading
Tests were conducted on the possibility of spreading a certain quantity of manure on pastures, making it possible to avoid the over-fertilisation (and pollution) of cultivated land. Two spreadings per year (the first at the end of the winter (which requires good soil condition), the second in May – June) were performed for several consecutive years.
Results of this study show that spreading manure on pasture isn’t detrimental to animal performance (in dairy production) even if there is a slight reduction in insignificant fat content (41.5 g/kg with manure against 42.1 g/kg gross without).
On the contrary, for the yield of plots, the contribution of nitrogen from winter manure was very valued, increasing the height of grass by 0.8 and 0.4 cm during the third and fourth years. Meanwhile, spring spreading decreased the yield (by 8% in the tests) in the case of insufficient rainfall. In the case of too much rainfall, nitrogen mineralises less and becomes more volatile, while manure is not integrated very well into the soil (slightly slowing down plant photosynthesis).