A long-term slurry experiment at AFBI Hillsborough continues to show how soil can accumulate carbon even under an intensive nutrient application and cutting regime.
The work, which involves 48 different plots, is the world’s longest running experiment looking at the impact of slurry on soils. At an event last Thursday to celebrate 50 years of the study, Dr Dario Fornara from AFBI highlighted how long-term experiments are important in providing good science-based evidence to inform policymakers.
Given the reliance of NI on permanent grassland, which makes up 90% of farmland here, the work at Hillsborough is an important contributor to understanding the extent to which emissions from agriculture can be offset by carbon sequestered in the soil.
Previous published work by Dr Fornava has suggested that sequestration in grassland soils can offset between 9% and 25% of overall greenhouse gas emissions from dairy and beef farms.
The plots at Hillsborough receive eight different nutrient treatments, including a control that is un-fertilised, a plot that receives inorganic NPK fertiliser and plots which receive three different rates of either cattle or pig slurry.
The slurry is applied at either 50, 100 or 200m3/ha/yr. Slurry applied at 50m3/ha equates to around 4,500 gallons per acre.
The nutrients are applied at three different intervals across the year, and the grass is cut three times.
The study was established in 1970 in response to a move by farmers towards slatted tanks, and continues to show that soils in the plots have not yet reached carbon saturation, despite intensive management.
However, it is the plots receiving the cattle slurry that are accumulating the most carbon, and at the highest rate of slurry application, the rate of carbon sequestration is more than double the control plots.
In contrast, there is no significant difference between the plots that get either pig slurry or NPK fertiliser when compared to the controls receiving no nutrients.
The results also show that carbon is being accumulated in the top 15cm of soil, not further down.
Two years ago, half the plots in the trial were ploughed and sowed out in a multi-species sward.
According to Dr Fornara, it is too early to say what impact ploughing has had on carbon stocks, or whether a MSS has the potential to sequester more carbon than a typical ryegrass sward. However, some data should be available next year.
Also speaking at the event, Dr Jonathan Storkey from Rothamsted Research in England, gave an overview of the Park Grass experiment, the longest running grassland study in the world.
Established in 1856 to compare growth between organic and inorganic fertiliser, the soil and plant samples taken down the years give an insight into how changes in the atmosphere, such as pollution, have impacted on soil fertility and plant biodiversity.
However, Storkey highlighted concerns that modern ways of funding research (often on a three to five year cycle) do not fit with this type of work.